WO2025109476A1

WO2025109476A1 - Methods and systems for providing respiratory support

Info

Publication number: WO2025109476A1
Application number: PCT/IB2024/061587
Authority: WO
Inventors: Thomas Heinrich Barnes; Hamish Adrian OSBORNE; Cameron Leslie MATTHEWS; Rachael GLAVES; Matthew Jon Payton; Mark Andrew THOMPSON; Anthony Behram ZEMKE
Original assignee: Fisher and Paykel Healthcare Ltd
Current assignee: Fisher and Paykel Healthcare Ltd
Priority date: 2023-11-20
Filing date: 2024-11-20
Publication date: 2025-05-30
Anticipated expiration: 2026-05-20

Abstract

A method of providing respiratory support to a patient during a medical procedure comprises: providing a gases flow to the patient via a patient interface system having at least one outflow vent; controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; and controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow through the at least one outflow vent at a second exhaust flow rate. A first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is different than a second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

Description

METHODS AND SYSTEMS FOR PROVIDING RESPIRATORY SUPPORT

Cross-reference to related applications

[0001] This application claims priority from US Application No. 63/601,152 filed on 20 November 2023, the contents of which are to be taken as incorporated herein by this reference.

Technical Field

[0002] The present invention relates to methods, systems and devices for providing respiratory support to a patient. It relates particularly, but not exclusively, to provision of respiratory support involving high flows of gases.

Background of Invention

[0003] Patients with diminished respiratory function or risk of diminished respiratory function can benefit from high flow respiratory support (which can include high flow therapy). Nasal high flow (NHF) is a form of high flow respiratory support, and can be beneficial for patients undergoing anaesthetic procedures including sedation and general anaesthesia by for example, improving dead space clearance in the airways and reducing the risk of hypoxaemia. High flow respiratory support may also be used in ICUs, wards, emergency departments or any other situation where respiratory support is provided.

[0004] However in certain situations, for example in anaesthetic procedures, residual risk of hypoxaemia remains during apnoea or spontaneous breathing for some patients, even when these patients are receiving NHF respiratory support. This can be due to physiological reasons such as upper and/or lower airway obstructions, mouth breathing and pulmonary shunt, to name a few. This may lead to complications arising from a low oxygen reservoir in the lungs, delivery of low levels of 02 to the lungs and faster desaturation where blood oxygen levels drop to low levels. It would be desirable to lessen the risk of patient harm associated with these complications.

A discussion or reference herein to any documents, acts, materials, devices, articles and the like or any other matter identified as prior art including any discussion in the background of invention, included to explain the context of the present application. It is not to be taken as an admission or a suggestion that any of the material was published, known or part of the common general knowledge.

Summary of Invention

[0005] Embodiments of the present disclosure are directed to systems, methods and devices for providing respiratory support to a patient with diminished respiratory function, or is at risk of diminished respiratory function.

[0006] Viewed from one aspect, the present disclosure provides a method of providing respiratory support to a patient during a medical procedure, the method comprising: providing a gases flow to the patient via a patient interface system having at least one outflow vent; controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; and controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow through the at least one outflow vent at a second exhaust flow rate; wherein a first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is different than a second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

[0007] Viewed from another aspect, the present disclosure provides a method of providing respiratory support to a patient during a medical procedure, the method comprising: providing a gases flow to the patient via a patient interface system having at least one outflow vent; controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a second rate of change in the second interface pressure associated with the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate.

[0008] In some embodiments, the methods comprise controlling the gases flow at the first supply flow rate before the second supply flow rate. In some embodiments, the methods comprise controlling the gases flow at the second supply flow rate before the first supply flow rate. The second supply flow rate may be higher than the first supply flow rate, or vice versa in some embodiments.

[0009] In some embodiments, the first supply flow rate is greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, or about 50 LPM. In some embodiments, the second supply flow rate is greater than about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM. However these ranges are examples only and are not limiting on the flow rates that may be supplied according to embodiments of the disclosure.

[0010] In some embodiments, the methods comprise providing the second supply flow rate in response to an indication of a patient condition. The patient condition may comprise e.g. a patient state or a patient parameter value. The indication of the patient condition may be determined by one or more of: observation of the patient and/or patient parameters; user confirmation of administration of therapy (such as an anaesthetic agent) to the patient; measurement of one or more patient parameters; a control device using data received from a user or one or more devices monitoring patient parameters to determine the indication of the patient condition; and the patient self-describing their condition.

[0011] In some embodiments, the one or more patient parameters comprise: depth of sedation; heart rate; EEG signal values; EKG/ECG signal values; EMG signal values; blood oxygen concentration; blood oxygen saturation (SpO2); expired oxygen concentration; blood CO2 concentration; transcutaneous CO2 concentration (TcCO2); transcutaneous 02 concentration (TcO2); expired CO2 concentration; and blood glucose level.

[0012] In some embodiments, the patient condition comprises a condition selected from a group comprising: lower or upper airway obstruction; soft palate obstruction; absence of spontaneous breathing; patient inspiratory demand not being met; the patient is or is at risk of becoming apnoeic; patient depth of sedation being met; and expiratory airway pressure is, or is approaching, a non-optimal threshold.

[0013] In some embodiments, the methods comprise controlling the first and/or second supply flow rate by one or more of: - manual selection by a user of the second supply flow rate in response to the user confirming the indication of the patient condition;

- a control device determining the second supply flow rate when the control device receives a user input confirming the indication of the patient condition; and

- a control device determining the second supply flow rate when the control device determines the existence of the patient condition using data received from one or more devices monitoring patient condition parameters.

[0014] In some embodiments, the methods comprise providing the first supply flow rate before delivery of an anaesthetic agent to the patient, and providing the second supply flow rate after delivery of an anaesthetic agent to the patient. In some embodiments, the methods comprise providing the second supply flow rate in response to an indication that an anaesthetic agent is being or has been delivered to the patient.

[0015] In some embodiments, the indication that an anaesthetic agent is being or has been delivered to the patient may be determined by one or more of:

- clinician observation of the patient and/or patient parameters and manual entry of the indication to a control device; and

- a control device using data received from a user or one or more devices monitoring patient parameters that provide an indication of an anaesthetic agent being or having been delivered to the patient.

[0016] In some embodiments, the methods comprise providing the respiratory support prior to anaesthetic agent delivery and/or prior to onset of anaesthesia or sedation in the patient.

[0017] In some embodiments, the methods comprise controlling the gases flow at a third supply flow rate and generating a third interface pressure and an exhaust flow through the at least one outflow vent at a third exhaust flow rate, wherein a rate of change in the third interface pressure associated with a change in the third exhaust flow rate is less than a rate of change in the second interface pressure associated with a change in the second exhaust flow rate. [0018] In some embodiments, the methods comprise controlling the gases flow at a third supply flow rate and generating a third interface pressure and an exhaust flow rate through the at least one outflow vent at a third exhaust flow rate, wherein a third predetermined resistance to flow of the at least one outflow vent at the third exhaust flow rate is different than the second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

[0019] In some embodiments, the third supply flow rate is lower than the second supply flow rate.

[0020] In some embodiments, the methods comprise providing the third supply flow rate in response to an indication of a different patient condition. The different patient condition may comprises a condition selected from a group comprising: lower or upper airway becoming patent; soft palate no longer obstructing; presence of spontaneous breathing; patient inspiratory demand being met; predetermined level of alertness being met; and expiratory interface pressure meets or exceeds an optimal threshold.

[0021] In some embodiments, the first rate of change in the first interface pressure may be in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l for a first exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM.

[0022] In some embodiments, the second rate of change in the second interface pressure may be in a range of greater than about 0.1 cmH2O/Lmin-l to less than about 0.6 cmH2O/Lmin-l, or about 0.15 cmH2O/Lmin-l to about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM. [0023] In some embodiments, the respective interface pressure and exhaust flow rate of the first rate of change and the second rate of change are related such that when presented graphically, their relationship comprises one or more of:

- a stepwise change between the first rate of change and the second rate of change;

- a gradual change between the first rate of change and the second rate of change;

- a curvilinear change between the first rate of change and the second rate of change;

- a non-constant gradient in a portion of the first rate of change and/or the second rate of change;

- a non-step change at a transition between the first exhaust flow rate and the second exhaust flow rate;

- a non-step change at a transition between the second exhaust flow rate and a third exhaust flow rate.

[0024] In some embodiments, one or both of the first rate of change and the second rate of change is non-constant.

[0025] In some embodiments, the methods comprise controlling the gases flow and generating one or more of:

- a first exhaust flow rate of about 40 LPM and a first interface pressure of about 3-5 cmH20, such as about 4 cm H2O;

- a first exhaust flow rate of about 30 LPM a first interface pressure of about 2-4 cmH20, such as about 3 cmH20;

- a second exhaust flow rate of about 50 LPM and a second interface pressure of about 5-8 cmH20, such as about 6 cmH20;

- a second exhaust flow rate of about 55 LPM and a second interface pressure of about 6-8 cmH20;

- a second exhaust flow rate of about 60 LPM and a second interface pressure of about 7-9 cmH20; and

-a second exhaust flow rate of about 70 LPM and a second interface pressure of about 7-15 cmH20, such as about 9-12 cmH20, such as about 9-10 cm H2O or about 10-12 cmH20. [0026] In some embodiments, the methods comprise operating a flow source to provide the gases flow, wherein the flow source is controlled by a control device configured to receive user supplied control inputs and/or processor generated control inputs.

[0027] In some embodiments, the patient interface system comprises a patient interface configured to provide the gases flow into one or both of the patient's nares, and comprising at least one outflow vent configured to generate a predetermined interface pressure and a predetermined target exhaust flow rate out of the at least one outflow vent for a predetermined supply flow rate to the patient interface.

[0028] In some embodiments, the patient interface comprises at least one sealing element, such as a nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare to substantially limit escape of gases except via the at least one outflow vent.

[0029] In some embodiments, the methods comprise the step of placing the patient interface on the patient.

[0030] In some embodiments, the patient is undergoing a medical procedure during provision of the respiratory support, such as a scheduled medical procedure.

[0031] In some embodiments, the methods comprise providing anaesthetic agent to the patient.

[0032] In some embodiments, the gases flow provided at one or both of the first supply flow rate and the second supply flow rate comprises 100% 02 concentration.

[0033] In some embodiments, the rate of change is an average rate of change.

[0034] In some embodiments, the first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l. [0035] In some embodiments, the first exhaust flow rate is between more than about 0

LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM.

[0036] In some embodiments, the second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate is in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l.

[0037] In some embodiments, the second exhaust flow rate is between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM.

[0038] In some embodiments, the first and second resistance to flow at the respective exhaust flow rates, and/or the first and second rate of change, are measurable in a simulation test.

[0039] In some embodiments, the patient is not apnoeic during the provision of the respiratory support.

[0040] In some embodiments, for a given exhaust flow rate, the resistance to flow is attributable to the size and/or shape of the at least one outflow vent.

[0041] In some embodiments, a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

[0042] Viewed from another aspect, the present disclosure provides a method of providing respiratory support to a patient, the method comprising: -providing a gases flow to the patient via a patient interface system comprising at least one outflow vent and a sealing element that substantially limits escape of gases from the patient except via the at least one outflow vent; controlling a supply flow rate of the gases to the patient interface system and generating an interface pressure and an exhaust flow through the at least one outflow vent at an exhaust flow rate; wherein the interface pressure and the exhaust flow rate comprise a non-linear relationship.

[0043] In some embodiments, the non-linear relationship comprises a polynomial component, preferably of degree two.

[0044] In some embodiments, the patient interface system comprises a patient interface configured to provide the gases flow into one or both of the patient's nares, patient interface comprising a body portion comprising at least one outflow vent configured to generate a predetermined interface pressure and an associated predetermined exhaust flow rate out of the at least one outflow vent for a predetermined supply flow rate into the one or both nares.

[0045] In some embodiments, the patient interface system comprises a patient interface configured to provide the gases flow into one or both of the patient's nares, patient interface comprising a body portion comprising at least one outflow vent configured to generate a first resistance to flow at a first supply flow rate which is different than a second resistance to flow at a second supply flow rate.

[0046] In some embodiments, the sealing element comprises at least one nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare to substantially limit escape of gases except via the at least one outflow vent.

[0047] In some embodiments, the patient interface system comprises a patient interface comprising at least one gas delivery element configured to provide the gases flow into the nares of the patient, and the at least one outflow vent comprises at least one opening in an insert located in the nare around the nasal prong.

[0048] In some embodiments, a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

[0049] In some embodiments, the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. [0050] In some embodiments, the at least one outflow vent may comprise at least one small opening and at least one large opening.

[0051] In some embodiments, at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm.

[0052] In some embodiments, at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about lm,m to about 2 mm or about 2 mm to about 3mm.

[0053] In some embodiments, a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

[0054] In some embodiments, when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening.

[0055] In some embodiments, when in use, flows from the at least one small opening are directed towards the patient's mouth.

[0056] In some embodiments, when in use, flows from the at least one large opening are directed away from the patient's mouth.

[0057] In some embodiments, the patient interface is configured to generate an interface pressure during provision of the respiratory support.

[0058] In some embodiments, for a given exhaust flow rate, a resistance to flow is attributable to the size and/or shape of the at least one outflow vent.

[0059] In some embodiments, a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm². [0060] In some embodiments, the patient interface comprises at least one sampling port. The at least one sampling port may be couplable with or provide a gas sampling line to provide fluid communication of gases in the patient interface to at least one sensor. The at least one sensor may comprise, for example, a pressure, temperature, gas composition, CO2 or humidity sensor to name a few.

[0061] In some embodiments, the patient interface comprises at least one gas sampling conduit that is adjustable to locate a sampling tip at an oral region of the patient when in use. The gas sampling conduit may be attachable, such as removably attachable, to the patient interface.

[0062] In some embodiments, the patient interface comprises at least one access port that is normally closed and is openable to provide instrument access to the nasal cavity via the patient interface. The access port may comprise a valve such as a duck bill valve which is openable by insertion of an instrument. The access port may comprise a removable cover. The removable cover may comprise one or more of the at least one outflow vent.

[0063] In some embodiments, the supply flow rate is greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, or about 50 LPM, or about 60 LPM, or about 70 LPM, or about 80 LPM, or about 90 LPM or about 100 LPM, or about 110 LPM or about 120 LPM, or about 130 LPM, or about 140 LPM, or about 150 LPM. However these ranges are examples only and are not limiting on the flow rates that may be supplied according to embodiments of the disclosure.

[0064] In some embodiments, the method comprises controlling the first supply flow rate by one or more of:

- manual selection by a user of the supply flow rate in response to the user confirming an indication of a patient condition;

- a control device determining the supply flow rate when the control device receives a user input confirming the indication of a patient condition; and

- a control device determining the supply flow rate when the control device determines the existence of a patient condition using data received from one or more devices monitoring patient condition parameters. [0065] The patient condition may comprise a condition selected from a group comprising: lower or upper airway obstruction; soft palate obstruction; absence of spontaneous breathing; patient inspiratory demand not being met; the patient is or is at risk of becoming apnoeic; patient depth of sedation being met; and expiratory airway pressure is, or is approaching, a non-optimal threshold.

[0066] In some embodiments, the method comprises controlling the gases flow and generating one or more of:

- an exhaust flow rate of about 40 LPM and an interface pressure of about 3-5 cmH20, such as about 4 cm H2O;

- an exhaust flow rate of about 30 LPM and an interface pressure of about 2-4 cmH20, such as about 3 cmH20;

- an exhaust flow rate of about 50 LPM and an interface pressure of about 5-8 cmH20, such as about 6 cmH20;

- an exhaust flow rate of about 55 LPM and an interface pressure of about 6-8 cmH20;

- an exhaust flow rate of about 60 LPM and an interface pressure of about 7-9 cmH20; and

- an exhaust flow rate of about 70 LPM and an interface pressure of about 7-15 cmH20, such as about 9-12 cmH20, such as about 9-10 cm H2O or about 10-12 cmH20.

[0067] Viewed from another aspect, the present disclosure provides a patient interface for provision of respiratory support, the interface comprising: a gases flow path for provision of a gases flow to the patient (e.g. via nasal elements of the patient interface); at least one outflow vent configured to permit an exhaust flow of gases; and a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use; wherein the patient interface is configured to generate an interface pressure during provision of the respiratory support; and wherein the interface pressure and the exhaust flow rate through the at least one outflow vent comprise a non-linear relationship comprising a rate of change of the interface pressure in a range of more than 0.15 cmH2O/Lmin-l to less than 0.5 cmH2O/Lmin-l for an exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM. [0068] In some embodiments, the non-linear relationship comprises a rate of change of the interface pressure in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.1 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l for an exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM..

[0069] In some embodiments, the non-linear relationship comprises a polynomial component, preferably of degree two.

[0070] In some embodiments, the at least one outflow vent is configured to generate in use, a predetermined exhaust flow rate for a predetermined supply flow rate.

[0071] In some embodiments, the at least one outflow vent is configured to generate in use a predetermined interface pressure and an associated exhaust flow rate for a predetermined supply flow rate.

[0072] In some embodiments, a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

[0073] In some embodiments, the patient interface comprises at least one gas delivery element configured to provide the gases flow into the nares of the patient, and the at least one outflow vent comprises: at least one opening in at least one insert locatable in the nare around the nasal prong. The at least insert may be provided separately from the patient interface. In some embodiments, the at least one insert is provided separately from the patient interface. In some embodiments, the sealing element may be provided by the at least one insert.

[0074] In some embodiments, the patient interface comprises at least one gas delivery element configured to provide the gases flow into one or both of the patient's nares.

[0075] In some embodiments, the sealing element comprises at least one nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare. [0076] In some embodiments the sealing element is integrated with or into the gas delivery element. In some embodiments, the sealing element may comprise the at least one outflow vent.

[0077] In some embodiments, the patient interface comprises a body portion comprising the at least one outflow vent. The body portion may comprise a chamber between a gases inlet to the patient interface and the patient, the chamber comprising a restriction causing asymmetrical flow to the patient's nares.

[0078] In some embodiments, the patient interface comprises a gases delivery side member comprising a collapsible portion that closes or partially closes to reduce or stop flow through the first patient interface.

[0079] In some embodiments, the collapsible portion is configured to collapse upon application of a force arising from placement of a respiratory mask over the patient interface.

[0080] In some embodiments, the at least one outflow vent is sized to allow provision of a gases flow from the respiratory mask to the patient.

[0081] In some embodiments, the respiratory mask comprises a bag valve mask.

[0082] In some embodiments, the patient interface is configured to generate an asymmetrical flow profile into the patient's nares.

[0083] In some embodiments, the patient interface is configured to receive side entry of gases, preferably single side entry.

[0084] In some embodiments, the patient interface comprises at least one sampling port. The at least one sampling port may be couplable with or provide a gas sampling line to provide fluid communication of gases in the patient interface to at least one sensor. The at least one sensor may comprise, for example, a pressure, temperature, gas composition, CO2 or humidity sensor to name a few.

[0085] In some embodiments, the patient interface comprises at least one gas sampling conduit that is adjustable to locate a sampling tip at an oral region of the patient when in use. The gas sampling conduit may be attachable, such as removably attachable, to the patient interface.

[0086] In some embodiments, the patient interface comprises at least one access port that is normally closed and is openable to provide instrument access to the nasal cavity via the patient interface. The access port may comprise a valve such as a duck bill valve which is openable by insertion of an instrument. The access port may comprise a removable cover. The removable cover may comprise one or more of the at least one outflow vent.

[0087] In some embodiments, the patient interface comprises a headgear connector to stabilise the patient interface on the patient when in use.

[0088] In some embodiments, the patient interface comprises a retention mechanism configured to improve sealing by the sealing element.

[0089] In some embodiments, the at least one outflow vent is configured to generate in use, a pressure differential between the patient and atmosphere comprising about 7cmH2O to about 15cmH2O at a supply flow rate of about 70 L/min.

[0090] In some embodiments, the at least one outflow vent is configured to generate exhaust rates from the patient interface substantially corresponding to a supplied flow rate of gas while the patient's mouth is closed and during breath hold or while the patient is apnoeic.

[0091] In some embodiments, the at least one outflow vent is non-variable. For example the size and/or shape may be non-variable.

[0092] In some embodiments, the at least one outflow vent comprises a cross sectional shape comprising a circle, ellipse, oval, obround, quadrilateral, or squircle.

[0093] In some embodiments, wherein the at least one outflow vent comprises 1 or 2 or 3 or 4 or 5 or 6 discrete openings, or more such as 10, 15, 20, 25, 30, 35, 40, 45, 50 discrete openings, or considerably more such as 100, 150, 200 discrete openings or more or any number in between. [0094] In some embodiments, the at least one outflow vent comprises 6 discrete openings each having a cross sectional dimension of about 3 mm.

[0095] In some embodiments, the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape.

[0096] In some embodiments, the at least one outflow vent may comprise at least one small opening and at least one large opening.

[0097] In some embodiments, at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm.

[0098] In some embodiments, at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about lm,m to about 2 mm or about 2 mm to about 3mm.

[0099] In some embodiments, a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

[0100] In some embodiments, when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening.

[0101] In some embodiments, when in use, flows from the at least one small opening are directed towards the patient's mouth.

[0102] In some embodiments, when in use, flows from the at least one large opening are directed away from the patient's mouth.

[0103] In some embodiments, the patient interface is configured to generate an interface pressure during provision of the respiratory support. In some embodiments, the at least one outflow vent is shaped to generate transitional or turbulent flow characteristics, preferably at flow rates above about 50 LPM.

[0104] In some embodiments, the interface pressure comprises mean interface pressure. [0105] In some embodiments, the rate of change is an average rate of change. In other embodiments, the rate of change is an instantaneous rate of change.

[0106] In some embodiments, the rate of change is determined in the absence of effects from patient breathing.

[0107] In some embodiments, the patient interface comprises a vent member comprising the at least one outflow vent. In some embodiments, the vent member may be removable to provide instrument access to the nasal cavity via the patient.

[0108] Viewed from another aspect, the present disclosure provides a method of providing respiratory support to a patient, the method comprising: using a first patient interface to provide a first respiratory support to the patient; placing a second patient interface over the first patient interface to reduce or stop flow of the first respiratory support to the first patient interface; and providing a second respiratory support using the second patient interface; wherein the first patient interface comprises at least one vent sized such that the second respiratory support from the second patient interface can be provided to the patient via the first patient interface.

[0109] In some embodiments, the patient interface comprises at least one nasal prong configured to provide the first respiratory support into at least one of the patient's nares.

[0110] In some embodiments, the first patient interface comprises at least one sealing element comprising a nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare to substantially limit escape of gases except via the at least one vent.

[0111] In some embodiments, the first patient interface comprises a body portion comprising the at least one vent.

[0112] In some embodiments, the first patient interface comprises a gases delivery side member comprising a collapsible portion that closes or partially closes to reduce or stop flow through the first patient interface. [0113] In some embodiments, the collapsible portion is configured to collapse upon application of a force arising from placement of the second patient interface over the first patient interface.

[0114] In some embodiments, the first respiratory support comprises: controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one vent at a first exhaust flow rate; and controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a second rate of change in the second interface pressure associated the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate.

[0115] In some embodiments, the at least one vent is configured to provide, for example:

- a first predetermined resistance to flow in use in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l for a first exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM; or when the supply flow rate is below 15 LPM; and

- a second predetermined resistance to flow in use in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

[0116] In some embodiments, the first respiratory support comprises providing a flow of gases at a supply flow rate to the patient interface and generating an interface pressure and an exhaust flow through the at least one vent at an exhaust flow rate, wherein values of interface pressure and values of exhaust flow rate comprise a non-linear relationship comprising a polynomial. [0117] In some embodiments, the non-linear relationship comprises a polynomial component, preferably of degree two.

[0118] In some embodiments, for a given exhaust flow rate, the resistance to flow may be attributable to the size and/or shape of the at least one vent.

[0119] In some embodiments, a total cross sectional area of the at least one vent may be in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

[0120] In some embodiments, the method comprises the step of locating the first patient interface, comprising at least one nasal sealing element, on the patient.

[0121] In some embodiments, the method comprises the step of removing the second patient interface to resume providing the first respiratory support.

[0122] In some embodiments, the second patient interface comprises a vent or expiratory path for exhausting gases.

[0123] In some embodiments, the method comprises the step of alternating between the first respiratory support and the second respiratory support by removal or application of the second patient interface.

[0124] In some embodiments, the second respiratory support is provided to achieve one or more of, for example: increase in patient oxygenation; delivery of one or more substances to the patient's airway; change in interface pressure; change in gases flow rate; different control over interface pressure; and different control over gases flow rate.

[0125] In some embodiments, the at least one vent is non-variable. For example the size and/or shape may be non-variable.

[0126] In some embodiments, the at least one vent comprises a cross sectional shape comprising a circle, ellipse, oval, obround, quadrilateral, or squircle. [0127] In some embodiments, the at least one vent comprises 1 or 2 or 3 or 4 or 5 or 6 discrete openings, or more such as 10, 15, 20, 25, 30, 35, 40, 45, 50 discrete openings, or considerably more such as 100, 150, 200 discrete openings or more or any number in between.

[0128] In some embodiments, the at least one vent comprises 6 discrete openings each having a cross sectional dimension of about 3 mm.

[0129] In some embodiments, the at least one vent is shaped to generate transitional or turbulent flow characteristics, preferably at flow rates above about 50 LPM.

[0130] In some embodiments, the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. In some embodiments, the at least one outflow vent may comprise at least one small opening and at least one large opening.

[0131] In some embodiments, at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm. In some embodiments, at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about lm,m to about 2 mm or about 2 mm to about 3mm.

[0132] In some embodiments, a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

[0133] In some embodiments, when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening. In some embodiments, when in use, flows from the at least one small opening are directed towards the patient's mouth. In some embodiments, when in use, flows from the at least one large opening are directed away from the patient's mouth.

[0134] In some embodiments, the second patient interface comprises a mask, such as a bag valve mask.

[0135] In some embodiments, the interface pressure comprises mean interface pressure. [0136] Viewed from another aspect, the present disclosure provides a system for providing respiratory support to a patient, the system comprising: a patient interface system for providing a flow of gases to the patient, the patient interface system having at least one outflow vent; and a gases source controllable to: provide a gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; and provide a gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is different than a second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

[0137] Viewed from another aspect, the present disclosure provides a system for providing respiratory support to a patient, the system comprising: a patient interface system for providing a flow of gases to the patient, the patient interface system having at least one outflow vent; and a gases source controllable to: provide a gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; and provide a gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a second rate of change in the second interface pressure associated with a change in the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with a change in the first exhaust flow rate.

[0138] In some embodiments, the system may comprise a controller for controlling the gases source, the controller comprising one or more of:

- a control device comprising a processor for calculating one or both of the first supply flow rate and the second supply flow rate based on one or more user inputs and/or other signals received by the processor; and

- a control selector for direct selection by a user of one or both of the first supply flow rate and the second supply flow rate.

[0139] In some embodiments, the system may comprise a humidifier. [0140] In some embodiments, the controller controls the gases flow at the first supply flow rate before the second supply flow rate.

[0141] In some embodiments, the controller controls gases flow at the second supply flow rate before the first supply flow rate.

[0142] In some embodiments, the second supply flow rate is higher than the first supply flow rate.

[0143] In some embodiments, the first supply flow rate is greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, or about 50 LPM.

[0144] In some embodiments, the second supply flow rate is greater than about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM.

[0145] In some embodiments, the second supply flow rate is provided in response to an indication of a patient condition.

[0146] In some embodiments, the indication of the patient condition may be determined by one or more of:

- observation of the patient and/or patient parameters;

- user confirmation of administration of therapy to the patient;

- instrumented measurement of one or more patient parameters;

- a control device using data received from a user or one or more devices monitoring patient parameters to determine the indication of the patient condition; and

- the patient self-describing their condition.

[0147] In some embodiments, the one or more patient parameters may comprise e.g. depth of sedation; heart rate; EEG signal values; EKG/ECG signal values; EMG signal values; blood oxygen concentration; blood oxygen saturation (SpO2); expired oxygen concentration; blood CO2 concentration; transcutaneous CO2 concentration (TcCO2); transcutaneous 02 concentration (TcO2), expired CO2 concentration; and blood glucose level.

[0148] In some embodiments, the patient condition comprises a condition selected from a group comprising: lower or upper airway obstruction; soft palate obstruction; absence of spontaneous breathing; patient inspiratory demand not being met; the patient is or is at risk of becoming apnoeic; patient depth of sedation being met; and expiratory airway pressure is, or is approaching, a non-optimal threshold.

[0149] In some embodiments, the controller is operable to control the first and/or second supply flow rate by one or more of: manual selection by a user of the second supply flow rate in response to the user confirming the indication of the patient condition; a control device determining the second supply flow rate when the control device receives a user input confirming the indication of the patient condition; and a control device determining the second supply flow rate when the control device determines the existence of the patient condition using data received from one or more devices monitoring patient condition parameters.

[0150] In some embodiments, the system may be operable to provide the first supply flow rate before delivery of an anaesthetic agent to the patient, and providing the second supply flow rate after delivery of an anaesthetic agent to the patient.

[0151] In some embodiments, the system may be operable to provide the second supply flow rate in response to an indication that an anaesthetic agent is being or has been delivered to the patient.

[0152] In some embodiments, the indication that an anaesthetic agent is being or has been delivered to the patient is determined by one or more of: clinician observation of the patient and/or patient parameters and manual entry of the indication to a control device; and a control device using data received from a user or one or more devices monitoring patient parameters that provide an indication of an anaesthetic agent being or having been delivered to the patient.

[0153] In some embodiments, the system may be operable to provide the respiratory support prior to anaesthetic agent delivery and/or prior to onset of anaesthesia or sedation in the patient.

[0154] In some embodiments, the system may be operable to control the gases flow at a third supply flow rate and generating a third interface pressure and an exhaust flow through the at least one outflow vent at a third exhaust flow rate, wherein a rate of change in the third interface pressure associated with a change in the third exhaust flow rate is less than a rate of change in the second interface pressure associated with a change in the second exhaust flow rate.

[0155] In some embodiments, the system may be operable to control the gases flow at a third supply flow rate and generating a third interface pressure and an exhaust flow rate through the at least one outflow vent at a third exhaust flow rate, wherein a third predetermined resistance to flow of the at least one outflow vent at the third exhaust flow rate is different than the second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

[0156] In some embodiments, the third supply flow rate is lower than the second supply flow rate.

[0157] In some embodiments, the system may be operable to provide the third supply flow rate in response to an indication of a different patient condition.

[0158] In some embodiments, the different patient condition comprises a condition selected from a group comprising e.g.: lower or upper airway becoming patent; soft palate no longer obstructing; presence of spontaneous breathing; patient inspiratory demand being met; predetermined level of alertness being met; and expiratory interface pressure meets or exceeds an optimal threshold.

[0159] In some embodiments, the first rate of change may be in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l for a first exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM.

[0160] In some embodiments, the second rate of change may be in a range of greater than about 0.1 cmH2O/Lmin-l to less than about 0.6 cmH2O/Lmin-l, or about 0.15 cmH2O/Lmin-l to about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about

70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

[0161] In some embodiments, the respective interface pressure and exhaust flow rate of the first rate of change and the second rate of change are related such that when presented graphically, their relationship comprises one or more of: a stepwise change between the first rate of change and the second rate of change; a gradual change between the first rate of change and the second rate of change; a curvilinear change between the first rate of change and the second rate of change; a non-constant gradient in a portion of the first rate of change and/or the second rate of change; a non-step change at a transition between the first exhaust flow rate and the second exhaust flow rate; and a non-step change at a transition between the second exhaust flow rate and a third exhaust flow rate.

[0162] In some embodiments, one or both of the first rate of change and the second rate of change is non-constant.

[0163] In some embodiments, the system may be operable to control the gases flow and generating one or more of:

-a second exhaust flow rate of about 70 LPM and a second interface pressure of about 7-15 cmH20, such as about 9-12 cmH20, such as about 9-10 cm H2O or about 10-12 cmH20.

[0164] In some embodiments, the gases source is controlled by a control device configured to receive user supplied control inputs and/or processor generated control inputs. [0165] In some embodiments, the patient interface system comprises a patient interface configured to provide the gases flow into one or both of the patient's nares, and comprising at least one outflow vent configured to generate a predetermined interface pressure and a predetermined target exhaust flow rate out of the at least one outflow vent for a predetermined supply flow rate to the patient interface.

[0166] In some embodiments, the patient interface comprises at least one sealing element, such as a nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare to substantially limit escape of gases except via the at least one outflow vent.

[0167] In some embodiments, the system may be operable to provide respiratory support to a patient undergoing a medical procedure, such as a scheduled medical procedure.

[0168] In some embodiments, the gases flow provided at one or both of the first supply flow rate and the second supply flow rate comprises 100% 02 concentration.

[0169] In some embodiments, the rate of change is an average rate of change.

[0170] In some embodiments, the first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l.

[0171] In some embodiments, the first exhaust flow rate is between more than about 0 LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM.

[0172] In some embodiments, the second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate is in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l. [0173] In some embodiments, the second exhaust flow rate is between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM.

[0174] Viewed from another aspect, the present disclosure provides a system for providing respiratory support to a patient, the system comprising: a patient interface system for providing a gases flow to the patient, the patient interface system comprising at least one outflow vent and a seal that substantially limits escape of gases from the patient except via the at least one outflow vent; and a gases source controllable to: provide a flow rate of the gases to the patient interface system and generate an interface pressure at the patient and an exhaust flow through the at least one outflow vent at an exhaust flow rate when in use; wherein the interface pressure and the exhaust flow rate comprise a non-linear relationship.

[0175] In some embodiments, the non-linear relationship comprises a polynomial component, preferably of degree two.

[0176] Viewed from another aspect, the present disclosure provides a system for providing respiratory support to a patient, the system comprising: a first patient interface for providing a first respiratory support to the patient, the first patient interface comprising at least one vent sized to allow a second respiratory support to be provided to the patient while flow of the first respiratory support to the first patient interface has been reduced or stopped; one or more flow sources providing a gases flow for one or both of the first respiratory support and the second respiratory support; and a controller for controlling the one or more flow sources.

[0177] In some embodiments, the system comprises or is operable with a second patient interface configured to reduce or stop flow of the first respiratory support to the first patient interface when placed over the first patient interface, and to provide the second respiratory support.

[0178] In some embodiments, the first patient interface comprises at least one nasal delivery element configured to provide the first respiratory support into at least one of the patient's nares. In some embodiments, the at least one nasal delivery element comprises a nasal prong or nasal pillow.

[0179] In some embodiments, the first patient interface comprises at least one sealing element. In some embodiments, the at least one sealing element comprises a nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare to substantially limit escape of gases except via the at least one vent.

[0180] In some embodiments, the first patient interface comprises a body portion comprising the at least one vent.

[0181] In some embodiments, the first patient interface comprises a gases delivery side member comprising a collapsible portion that closes or partially closes to reduce or stop flow through the first patient interface. The collapsible portion may be configured to collapse upon application of a force arising from placement of the second patient interface over the first patient interface.

[0182] In some embodiments, the first respiratory support comprises: controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one vent at a first exhaust flow rate; and controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a second rate of change in the second interface pressure associated the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate.

[0183] In some embodiments, the at least one vent is configured to provide:

- a second predetermined resistance to flow in use in a range of greater than about 0.15 cmH20/Lmin-l to less than about 0.5 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.4 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.3 cmH20/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

[0184] In some embodiments, a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

[0185] In some embodiments, the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. In some embodiments, the at least one outflow vent may comprise at least one small opening and at least one large opening. In some embodiments, at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm. In some embodiments, at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about lm,m to about 2 mm or about 2 mm to about 3mm.

[0186] In some embodiments, a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

[0187] In some embodiments, when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening. In some embodiments, when in use, flows from the at least one small opening are directed towards the patient's mouth. In some embodiments, when in use, flows from the at least one large opening are directed away from the patient's mouth.

[0188] In some embodiments, the patient interface comprises at least one sampling port. The at least one sampling port may be couplable with or provide a gas sampling line to provide fluid communication of gases in the patient interface to at least one sensor. The at least one sensor may comprise, for example, a pressure, temperature, gas composition, CO2 or humidity sensor to name a few. [0189] In some embodiments, the patient interface comprises at least one gas sampling conduit that is adjustable to locate a sampling tip at an oral region of the patient when in use. The gas sampling conduit may be attachable, such as removably attachable, to the patient interface.

[0190] In some embodiments, the patient interface comprises at least one access port that is normally closed and is openable to provide instrument access to the nasal cavity via the patient interface. The access port may comprise a valve such as a duck bill valve which is openable by insertion of an instrument. The access port may comprise a removable cover. The removable cover may comprise one or more of the at least one outflow vent.

[0191] In some embodiments, the first respiratory support comprises providing a flow of gases at a supply flow rate to the patient interface and generating an interface pressure and an exhaust flow through the at least one vent at an exhaust flow rate, wherein values of interface pressure and values of exhaust flow rate comprise a non-linear relationship.

[0192] In some embodiments, the non-linear relationship comprises a polynomial component, preferably of degree two.

[0193] In some embodiments, operation of the system requires location of the first patient interface, comprising at least one nasal sealing element, on the patient.

[0194] In some embodiments, operation of the system requires removal of the second patient interface to resume providing the first respiratory support.

[0195] In some embodiments, the second patient interface comprises a vent or expiratory path for exhausting gases.

[0196] In some embodiments, the system is operable to alternate between the first respiratory support and the second respiratory support by removal or application of the second patient interface.

[0197] In some embodiments, the second respiratory support is provided to achieve one or more of: increase in patient oxygenation; delivery of one or more substances to the patient's airway; change in interface pressure; change in gases flow rate; different control over interface pressure; and different control over gases flow rate.

[0198] In some embodiments, the at least one vent is non-variable. For example the size and/or shape may be non-variable.

[0199] In some embodiments, the at least one vent comprises a cross sectional shape comprising a circle, ellipse, oval, obround, quadrilateral, or squircle.

[0200] In some embodiments, the at least one vent comprises 1 or 2 or 3 or 4 or 5 or 6 discrete openings, or more such as 10, 15, 20, 25, 30, 35, 40, 45, 50 discrete openings, or considerably more such as 100, 150, 200 discrete openings or more or any number in between.

[0201] In some embodiments, the at least one vent comprises 6 discrete openings each having a cross sectional dimension of about 3 mm.

[0202] In some embodiments, the at least one vent is shaped to generate transitional or turbulent flow characteristics, preferably at flow rates above about 50 LPM.

[0203] In some embodiments, the second patient interface comprises a mask, such as a bag valve mask.

[0204] In some embodiments, the interface pressure comprises mean interface pressure.

[0205] Viewed from another aspect, the present disclosure provides a patient interface for provision of respiratory support, the interface comprising:

- a gases flow path for provision of a gases flow to the patient;

- at least one outflow vent configured to permit an exhaust flow of gases; and

- a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use; wherein the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. [0206] It will be appreciated that the sealing element substantially prevents escape of gas from the patient except via the at least one outflow vent when the patient interface is in use with the patient's mouth closed or covered.

[0207] In some embodiments, the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. In some embodiments, the at least one outflow vent may comprise at least one small opening and at least one large opening. In some embodiments, at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm. In some embodiments, at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about lm,m to about 2 mm or about 2 mm to about 3mm.

[0208] In some embodiments, a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

[0209] In some embodiments, when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening. In some embodiments, when in use, flows from the at least one small opening are directed towards the patient's mouth. In some embodiments, when in use, flows from the at least one large opening are directed away from the patient's mouth.

[0210] In some embodiments, the patient interface is configured to generate an interface pressure during provision of the respiratory support.

[0211] Viewed from another aspect, the present disclosure provides a patient interface for provision of respiratory support, the patient interface comprising: a gases flow path for provision of a gases flow to the patient; at least one outflow vent configured to permit an exhaust flow of gases at an exhaust flow rate; and a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use; wherein the at least one outflow vent has a predetermined resistance to flow in use.

[0212] In some embodiments, the predetermined resistance to flow of the at least one outflow vent is in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin- 1, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH20/Lmin-l when the exhaust flow rate is between more than about 0 LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM .

[0213] In some embodiments, the predetermined resistance to flow of the at least one outflow vent is in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l when the exhaust flow rate is between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM.

[0214] In some embodiments, the predetermined resistance to flow is measurable in a simulation test.

[0215] In some embodiments, in use, a supply flow rate is provided to the patient interface to generate an interface pressure and the exhaust flow through the at least one outflow vent at the exhaust flow rate. .

[0216] In some embodiments, a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

[0217] In some embodiments, the patient interface comprises at least one gas delivery element configured to provide the gases flow into the nares of the patient, and the at least one outflow vent comprises at least one opening in at least one insert locatable in the nare around the at least one gas delivery element.

[0218] In some embodiments, the sealing element is provided by the at least one insert.

[0219] In some embodiments, the at least one insert is provided separately from the patient interface. [0220] In some embodiments, the patient interface comprises at least one gas delivery element configured to provide the gases flow into one or both of the patient's nares.

[0221] In some embodiments, the sealing element comprises at least one nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare.

[0222] In some embodiments, the sealing element is integrated with or into the gas delivery element. In some embodiments, the sealing element comprises the at least one outflow vent.

[0223] In some embodiments, the patient interface comprises a body portion comprising the at least one outflow vent.

[0224] In some embodiments, the body portion comprises a chamber between a gases inlet to the patient interface and the patient, the chamber comprising a restriction causing asymmetrical flow to the patient's nares.

[0225] In some embodiments, the patient interface comprises a gases delivery side member comprising a collapsible portion that closes or partially closes to reduce or stop flow through the first patient interface.

[0226] In some embodiments, the collapsible portion is configured to collapse upon application of a force arising from placement of a respiratory mask over the patient interface.

[0227] In some embodiments, the at least one outflow vent is sized to allow provision of a gases flow from the respiratory mask to the patient.

[0228] In some embodiments, the respiratory mask comprises a bag valve mask.

[0229] In some embodiments, the patient interface is configured to generate an asymmetrical flow profile into the patient's nares.

[0230] In some embodiments, the patient interface is configured to receive side entry of gases, preferably single side entry.

[0231] In some embodiments, the patient interface comprises at least one sampling port. [0232] In some embodiments, the at least one sampling port is couplable with or provides a gas sampling line to provide fluid communication of gases in the patient interface to at least one sensor. In some embodiments, the at least one sensor comprises a pressure, temperature, gas composition, CO2 or humidity sensor.

[0233] In some embodiments, the patient interface comprises at least one gas sampling conduit that is adjustable to locate a sampling tip at an oral region of the patient when in use. In some embodiments, the gas sampling conduit is attachable such as removably attachable, to the patient interface.

[0234] In some embodiments, the patient interface comprises at least one access port that is normally closed and is openable to provide instrument access to the nasal cavity via the patient interface. In some embodiments, the access port comprises a removable cover. The removable cover may comprise one or more of the at least one outflow vent.

[0235] In some embodiments, the patient interface comprises a headgear connector to stabilise the patient interface on the patient when in use.

[0236] In some embodiments, the patient interface comprises a retention mechanism configured to improve sealing by the sealing element.

[0237] The In some embodiments, the at least one outflow vent is configured to generate in use, a pressure differential between the patient and atmosphere comprising about 7cmH2O to about 15cmH2O at a supply flow rate of about 70 L/min.

[0238] In some embodiments, the at least one outflow vent is configured to generate exhaust rates from the patient interface substantially corresponding to a supplied flow rate of gas while the patient's mouth is closed and during breath hold or while the patient is apnoeic.

[0239] In some embodiments, the at least one outflow vent comprises a size and/or shape that is non-variable.

[0240] In some embodiments, the at least one outflow vent comprises a cross sectional shape comprising a circle, ellipse, oval, obround, quadrilateral, or squircle. [0241] In some embodiments, the at least one outflow vent comprises 1 or 2 or 3 or 4 or 5 or 6 discrete openings.

[0242] In some embodiments, the at least one outflow vent comprises 6 discrete openings each having a cross sectional dimension of about 3 mm.

[0243] In some embodiments, the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. In some embodiments, the at least one outflow vent comprises at least one small opening and at least one large opening. In some embodiments, the at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm. In some embodiments, the at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about 1 mm to about 2 mm or about 2 mm to about 3mm.

[0244] In some embodiments, a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

[0245] In some embodiments, when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening. In some embodiments, when in use, flows from the at least one small opening are directed towards the patient's mouth. In some embodiments, when in use, flows from the at least one large opening are directed away from the patient's mouth.

[0246] In some embodiments, the at least one outflow vent is shaped to generate transitional or turbulent flow characteristics, preferably at flow rates above about 50 LPM.

[0247] In some embodiments, the patient interface comprises a vent member comprising the at least one outflow vent. In some embodiments, the vent member is removable to provide instrument access to the nasal cavity via the patient interface.

[0248] Viewed from another aspect, the present disclosure provides a system for providing respiratory support to a patient, the system comprising: a patient interface for providing a gases flow to the patient, the patient interface having at least one outflow vent to permit an exhaust flow of gases at an exhaust flow rate, and a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use; a gases source operable to provide a gases flow; and a controller operable to control a flow rate of a gases flow provided to the patient interface at a predetermined supply flow rate; wherein the at least one outflow vent has a pre-determined resistance to flow in use.

[0249] In some embodiments, the system comprises a flow source controllable by the controller to provide the gases flow at the predetermined supply flow rate.

[0250] In some embodiments, the patient interface comprises a patient interface according to any one of the foregoing aspects.

[0251] In some embodiments, the system comprises a humidifier.

[0252] In some embodiments, the predetermined supply flow rate is in a range of greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM

[0253] In some embodiments, the controller is operable to control the predetermined supply flow rate at a first supply flow rate that is greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM or about 50 LPM.

[0254] In some embodiments, the controller is operable to control the predetermined supply flow rate at a second supply flow rate that is higher than the first supply flow rate and optionally, that is greater than about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM.

[0255] In some embodiments, the second supply flow rate is provided in response to an indication of a patient condition.

[0256] In some embodiments, the indication of the patient condition is determined by one or more of: observation of the patient and/or patient parameters; user confirmation of administration of therapy to the patient; instrumented measurement of one or more patient parameters; a control device using data received from a user or one or more devices monitoring patient parameters to determine the indication of the patient condition; and the patient self-describing their condition.

[0257] In some embodiments, the one or more patient parameters comprise: depth of sedation; heart rate; EEG signal values; EKG/ECG signal values; blood oxygen concentration; blood oxygen saturation (SpO2); expired oxygen concentration; blood CO2 concentration; transcutaneous CO2 concentration (TcCO2); transcutaneous 02 concentration (TcO2); expired C02 concentration; and blood glucose level.

[0258] In some embodiments, the patient condition comprises a condition selected from a group comprising: lower or upper airway obstruction; soft palate obstruction; absence of spontaneous breathing; patient inspiratory demand not being met; the patient is or is at risk of becoming apnoeic; patient depth of sedation being met; and expiratory airway pressure is, or is approaching, a non-optimal threshold.

[0259] In some embodiments, the controller is operable to control the first and/or second supply flow rate by one or more of: manual selection by a user of the second supply flow rate in response to the user confirming the indication of the patient condition; a control device determining the second supply flow rate when the control device receives a user input confirming the indication of the patient condition; and a control device determining the second supply flow rate when the control device determines the existence of the patient condition using data received from one or more devices monitoring patient condition parameters.

[0260] In some embodiments, the system is operable to provide a first supply flow rate before delivery of an anaesthetic agent to the patient, and providing a second supply flow rate after delivery of an anaesthetic agent to the patient.

[0261] In some embodiments, the system is operable to provide the second supply flow rate in response to an indication that an anaesthetic agent is being or has been delivered to the patient.

[0262] In some embodiments, the indication that an anaesthetic agent is being or has been delivered to the patient is determined by one or more of: clinician observation of the patient and/or patient parameters and manual entry of the indication to a control device; and a control device using data received from a user or one or more devices monitoring patient parameters that provide an indication of an anaesthetic agent being or having been delivered to the patient.

[0263] In some embodiments, the system is operable to provide the respiratory support prior to anaesthetic agent delivery and/or prior to onset of anaesthesia or sedation in the patient.

[0264] In some embodiments, the system is operable to control the gases flow at a third supply flow rate. In some embodiments, the third supply flow rate is less than the second supply flow rate.

[0265] In some embodiments, the system is operable to provide the third supply flow rate in response to an indication of a different patient condition.

[0266] In some embodiments, the different patient condition comprises a condition selected from a group comprising: lower or upper airway becoming patent; soft palate no longer obstructing; presence of spontaneous breathing; patient inspiratory demand being met; predetermined level of alertness being met; and expiratory interface pressure meets or exceeds an optimal threshold.

[0267] In some embodiments, the controller is configured to receive user supplied control inputs and/or processor generated control inputs.

[0268] In some embodiments, the patient interface is configured to provide the gases flow into one or both of the patient's nares.

[0269] In some embodiments, the system is operable to provide respiratory support to a patient undergoing a medical procedure, such as a scheduled medical procedure.

[0270] In some embodiments, the gases flow provided at the predetermined supply flow rate comprises 100% 02 concentration.

[0271] In some embodiments, a first predetermined resistance to flow of the at least one outflow vent at a first exhaust flow rate through the at least one outflow vent is in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.1 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l.

[0272] In some embodiments, the first exhaust flow rate is between more than about 0 LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM.

[0273] In some embodiments, a second predetermined resistance to flow of the at least one outflow vent at a second exhaust flow rate is in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l.

[0274] In some embodiments, the second exhaust flow rate is between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM.

[0275] In some embodiments, for a given exhaust flow rate, the resistance to flow is attributable to a size and/or shape of the at least one outflow vent.

[0276] In some embodiments, a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

[0277] In some embodiments, the system is operable to control the gases flow and generating one or more of: an exhaust flow rate of about 40 LPM and an interface pressure of about 3-5 cmH20, such as about 4 cm H2O; an exhaust flow rate of about 30 LPM an interface pressure of about 2-4 cmH20, such as about 3 cmH20; an exhaust flow rate of about 50 LPM and an interface pressure of about 5-8 cmH20, such as about 6 cmH20; an exhaust flow rate of about 55 LPM and an interface pressure of about 6-8 cmH20; an exhaust flow rate of about 60 LPM and an interface pressure of about 7-9 cmH20; and an exhaust flow rate of about 70 LPM and an interface pressure of about 7-15 cmH20, such as about 9- 12 cmH20, such as about 9-10 cm H2O or about 10-12 cmH20. [0278] It is to be understood that according to various aspects, embodiments and examples disclosed herein, the sealing element substantially prevents escape of gas from the patient except via the at least one outflow vent when the patient interface is in use. Sealing in this manner may be best achieved in use when the patient's mouth is closed or covered. Thus exhalation is via the nares into the patient interface, rather than exhalation via the mouth.

[0279] It is to be understood each of the various aspects described herein may incorporate one or more features, modifications and alternatives described in the context of one or more other aspects and may include one or more features, modifications and alternatives of any of the embodiments described below, as appropriate. For efficiency, such features, modifications and alternatives have not been repetitiously disclosed for each and every aspect although one of skill in the art will appreciate that such combinations of features, modifications and alternatives disclosed for some aspects and embodiments apply similarly for other aspects and are within the scope of and form part of the subject matter of this disclosure.

[0280] In order for the invention to be more readily understood and put into practice, one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings.

Brief Description of Drawings

[0281] The present invention will now be described in greater detail with reference to the accompanying drawings. It is to be understood that the embodiments shown are examples only and are not to be taken as limiting the scope of the invention as defined in the claims appended hereto.

[0282] Fig. 1 is a schematic illustration of a system for providing respiratory support according to embodiments of the disclosure.

[0283] Fig. 2 is a flow chart showing schematically a method of providing respiratory support in which a first predetermined resistance to flow (RTF) of the at least one outflow vent at the first exhaust flow rate is different than a second predetermined resistance to flow (RTF) of the at least one outflow vent at the second exhaust flow rate. [0284] Fig. 3 is a flow chart showing schematically a method of providing respiratory support wherein a second rate of change in the second interface pressure associated with the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate.

[0285] Fig. 4 represents a PQ profile representing a relationship between exhaust flow rate and interface pressure according to an embodiment of the disclosure.

[0286] Fig. 5 is a flow chart showing schematically a method of providing respiratory support to a patient wherein the interface pressure and the exhaust flow rate comprise a non-linear relationship.

[0287] Fig. 6 is a graphical representation of interface pressures and exhaust flow rates as may be generated according to embodiments of the present disclosure.

[0288] Fig. 7 is a graphical representation of interface pressure vs supply flow rates.

[0289] Fig. 8 is a schematic illustration of a patient interface according to an embodiment of the disclosure.

[0290] Fig 9 shows the patient interface of Fig. 8, rotated for a better view of the headgear connector and outflow vents.

[0291] Fig. 10 shows a patient wearing an embodiment of a patient interface according to the present disclosure, and a face mask.

[0292] Fig. 11 shows a cross-section of a portion of the patient interface of Fig. 10 in a first (substantially open) configuration and a second (substantially closed) configuration respectively.

[0293] Fig. 12 shows a patient interface having a channel through which a head strap may pass.

[0294] Fig. 13 shows a patient interface having one head strap connector located on the body portion, and an opposing head strap connector located on a gas delivery conduit. [0295] Fig. 14 shows a patient interface having head strap connectors located at a distance from the patient interface body portion.

[0296] Fig. 15 is a schematic cross-sectional view of a patient interface showing a chamber inside the body portion.

[0297] Fig. 16 is a schematic cross-sectional view of a patient interface showing a chamber inside the body portion and a restriction inside the chamber to generate asymmetrical interface pressure for asymmetrical flows to the nares.

[0298] Fig. 17 is a flow chart showing schematically, steps in such a method 700 of providing respiratory support which involves bag masking.

[0299] Fig. 18 shows a patient interface having at least one sampling port.

[0300] Fig. 19 shows a patient interface having sealing inserts applied to a patient interface.

[0301] Fig. 20 shows a patient interface wherein the at least one outflow vent comprises small and large openings.

[0302] Fig. 21 is a schematic illustration showing flows from the at least one outflow vent being directed towards the patient's mouth.

[0303] Fig. 22 is a schematic illustration showing flows from the at least one outflow vent being directed away from the patient's mouth.

[0304] Fig. 23 is a schematic illustration of part of a patient interface having an access port with a valve in a normally closed arrangement.

[0305] Fig. 24 shows the part of the patient interface from Fig. 23 with a tube inserted into the access port and the valve in an open arrangement.

[0306] Fig. 25 shows a patient interface having an access port which is formed when a vent member is removed from the patient interface. Detailed Description

[0307] There are many situations where a patient has diminished respiratory function, or is at risk of diminished respiratory function. One situation involves medical procedures in which the patient is provided anaesthesia to enable them to tolerate the procedures. Anaesthesia can include situations where the patient is conscious or where the patient is made unconscious (as opposed to falling into natural sleep). Due to the combination of anaesthetic agents administered to the patient to achieve sedation, the patient can become unable to maintain adequate airway protection and/or spontaneous ventilation. As such, the patient has diminished respiratory function, or is at risk of diminished respiratory function. This may also arise due to physiological reasons, with or without anaesthesia. In these situations, it may be desirable to provide respiratory support according to embodiments of the present disclosure.

[0308] NHF can provide a solution for meeting oxygenation and therapeutic requirements for patients during anaesthetic procedures. However, some patients may have underlying physiological reasons that inhibit the success or diminish the benefits of NHF. Some examples include: upper airway obstructions (includes nasal passages and the nasopharynx), for example soft palate closure; lower airway obstructions (includes the larynx, trachea, bronchial tree and the lungs); mouth breathing (entraining room air can dilute 02 concentration of delivered gases); and pulmonary shunt (i.e. deoxygenated blood moves from the right side to the left side of the heart without participating in gas exchange in the pulmonary vessels e.g. due to atelectasis).

[0309] In this specification, HF or "high flow" means, without limitation, any gas flow with a flow rate that is higher than usual/normal, such as higher than the normal inspiration flow rate of a healthy patient. Alternatively, or additionally, it can be higher than some other threshold flow rate that is relevant to the context - for example, where providing a gas flow to a patient at a flow rate to meet or exceed inspiratory demand, that flow rate might be deemed "high flow" as it is higher than a nominal flow rate that might have otherwise been provided. "High flow" is therefore context dependent, and what constitutes "high flow" depends on many factors such as the health state of the patient, type of procedure/therapy/support being provided, the nature of the patient (big, small, adult, child) and the like. Those skilled in the art would know from context what constitutes "high flow". It is a magnitude of flow rate that is over and above a flow rate that might otherwise be provided.

[0310] But, without limitation, some indicative values of high flow can be as follows.

[0311] In some configurations, delivery of gases to a patient at a flow rate of greater than or equal to about 5 or 10 litres per minute (5 or 10 LPM).

[0312] In some configurations, delivery of gases to a patient at a flow rate of about 5 LPM or about 10 LPM to about 150 LPM, or about 15 LPM to about 95 LPM, or about 20 LPM to about 90 LPM, or about 25 LPM to about 85 LPM, or about 30 LPM to about 80 LPM, or about 35 LPM to about 75 LPM, or about 40 LPM to about 70 LPM, or about 45 LPM to about 65 LPM, or about 50 LPM to about 60 LPM. For example, a flow rate of gases supplied or provided to a patient interface via a system or from a flow source or flow modulator, may comprise, but is not limited to, flows of at least about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 LPM, or more, and useful ranges may be selected to be between any of these values (for example, about 20 LPM to about 90 LPM, about 40 LPM to about 70 LPM, about 40 LPM to about 80 LPM, about 50 LPM to about 80 LPM, about 60 LPM to about 80 LPM, about 70 LPM to about 100 LPM, about 70 LPM to about 80 LPM).

[0313] In "high flow" the gas delivered will be chosen depending on for example the intended use of a therapy and/or respiratory support. Gases delivered may comprise a percentage of oxygen (also referred to herein as fraction or concentration of oxygen). In some configurations, the percentage of oxygen in the gases delivered may be about 15% to about 100%, 20% to about 100%, or about 30% to about 100%, or about 40% to about 100%, or about 50% to about 100%, or about 60% to about 100%, or about 70% to about 100%, or about 80% to about 100%, or about 90% to about 100%, or about 100%, or 100%.

[0314] Flow rates for "High flow" for premature/infants/paediatrics (with body mass in the range of about 1 to about 30 kg) can be different. The flow rate can be set to 0.4-8 LPM/kg with a minimum of about 0.5 LPM and a maximum of about 70 LPM. For patients under 2 kg maximum flow may be set to 8 LPM. [0315] High flow has been found effective in meeting or exceeding the patient's normal inspiratory flow, to increase oxygenation of the patient and/or reduce the work of breathing.

[0316] High flow may be used as a means to promote gas exchange and/or respiratory support through the delivery of high flows of oxygen and/or other gases, and through the removal of CO2 from the patient's airways. High flow may be particularly useful prior to, during or after a medical and/or anaesthetic procedure.

[0317] When used prior to a medical procedure, high gas flow can pre-load the patient with oxygen so that their blood oxygen saturation level and volume of oxygen in the lungs is higher to provide an oxygen buffer while the patient is in an apnoeic phase during the medical and/or anaesthetic procedure.

[0318] A continuous supply of oxygen can be useful for sustaining healthy respiratory function during medical procedures (such as during an anaesthetic procedure) where respiratory function might be compromised (e.g. diminishes or stops). When this supply is compromised, hypoxaemia and/or hypercapnia can occur. During anaesthetic procedures such as general anaesthesia where the patient may be unconscious, the patient may be monitored to detect when this happens. If oxygen supply is compromised, the clinician may stop the medical procedure and facilitate oxygen supply and/or CO2 removal. This can be achieved for example by manually ventilating the patient through an anaesthetic bag and mask, or by providing a high flow of gases to the patient's airway using a high flow respiratory system.

[0319] Further advantages of high gas flow can include that the high gas flow increases pressure in the airways of the patient, thereby providing pressure support that opens airways, the trachea, lungs/alveolar and bronchioles. The opening of these structures enhances oxygenation, and to some extent assists in removal of CO2.

[0320] The increased pressure can also keep structures such as the larynx from blocking the view of the vocal chords during intubation. When humidified, the high gas flow can also prevent airways from drying out, mitigating mucociliary damage, and reducing risk of laryngospasms and risks associated with airway drying such as nose bleeding, aspiration (as a result of nose bleeding), and airway obstruction, swelling and bleeding. [0321] However, when NHF is delivered via a non-sealing patient interface comprising prongs inserted in the patient's nares ("conventional NHF"), it has a large, uncontrollable and difficult to measure leak to (and from) ambient around the prongs. Therefore, for a given supply flow rate, there is inter-patient variability in the pressure within the patient's airway e.g. the nasal cavity and/or lower airways, as well as variability in the proportion of flow that is supplied to the patient's upper and lower airways. Additionally, entrainment of room air may reduce the effective fraction of inspired 02 (FiO2) of a spontaneously breathing patient, the fraction of 02 delivered to the patient's lungs in an apnoeic patient, and/or in a mouth open or closed situation. Air entrainment is typically higher at low supply flow rates especially when the supply flow rates are below the patient's inspiratory demand. However when a patient is mouth breathing, air entrainment can occur, even at higher supply flow rates above inspiratory demand. This effect is variable both over time as well as between patients and is hard to measure.

[0322] Since the clinician has little or no control over these factors using conventional NHF techniques, therapy can become sub-optimal due to e.g. insufficient pressure in the nasal cavity (based on the selection of patient interface size and predetermined flow rate), or due to some other reason, e.g. underlying pathology and/or physiology such as nasal obstruction precluding oxygenation nasally. Providing guidance and training for suitable supply flow rate selection is therefore an important aspect of NHF patient safety in current practice, but since this type of guidance is generalized, it is not always easy for a clinician to identify when or why NHF may not be successful for a particular patient, or what to do about it.

[0323] Respiratory support systems utilising sealing patient interfaces have been used in anaesthetic procedures. However such respiratory support systems are not flow controlled but pressure-controlled in that the supply flow of gasses is controlled to provide a target pressure rather than a target flow rate. A flow-controlled system may involve the control of supply flow rate as described herein. For example, a supply flow of gases can be set to a predetermined flow rate. The predetermined flow rate may be adjustable e.g. by controlling a proportional valve and/or blower motor speed, manual control of a flow meter, control by or using a control device and the like. The supply flow rate may remain substantially constant across a patient's breathing cycle. The supply flow rate may be substantially equal to the predetermined flow rate across a patient's breathing cycle. That is, the supply flow rate can be delivered independent of patient effects. The supply flow rate may be time varying, and/or the delivered oxygen concentration of the supply flow of gases may be time varying. This time-varying characteristic may be independent of the patient's breathing cycle.

[0324] The sealing patient interfaces utilised in pressure-controlled systems are intentionally designed with restrictive bias flow vents that provide a high resistance to flow of exhaust gases to provide pressure-controlled respiratory support. In use, supply flow of respiratory gases is limited to low flower rates to limit the pressures generated by the resistance to flow of the bias flow vents. As such, pressure-controlled respiratory support may not have the aforementioned benefits of high flow respiratory support. Furthermore, if used in a flow-controlled system these sealing interfaces can generate high patient pressures, particularly during patient exhalation. As such they are not suitable to be used with higher supply flow rates of gases, as might be provided in a flow-controlled system. In a flow- controlled system, the supply flow rate may be set to meet inspiratory demand, such as in HF respiratory support. To provide such a high flow rate through such a system with restrictive vents could present increasing risks to the patient, such as risk of barotrauma and/or gastric insufflation.

[0325] Embodiments of the present disclosure provide methods and systems for controlling a supply flow rate of a gas provided to a patient via a patient interface, and generating a patient interface pressure and an exhaust flow rate from the patient interface. In some embodiments, the interface pressure increases at a higher rate at higher exhaust flow rates than the interface pressure increases at lower exhaust flow rates. A patient interface system comprising outflow vents for escape of the exhaust flow of gases is also provided for use with the system and/or method. These outflow vents are sufficiently non- restrictive, providing a low resistance to flow (RTF), that permit safe provision of high flow respiratory support according to the embodiments disclosed. Non-restrictive outflow vents may generate greater noise when in use than outflow vents that are more restrictive. However it is understood that in the clinical environment for which the methods, systems and devices of the present disclosure are intended, this noise would have minimal impact on patient comfort given the level of background noise in e.g. operating theatres and wards. [0326] Referring to Figure 1, the respiratory system 100 comprises a flow source 104 for providing a gas flow 106 at a predetermined flow rate. The gas flow 106 may include pure oxygen (e.g. having a fraction of oxygen of 1, or concentration of oxygen of 100%), or a mixture of oxygen and one or more other gases. In alternative embodiments, the respiratory system 100 may have a connection for coupling to a flow source (not shown) that is external to and fluidly couplable with the respiratory system 100. As such, the flow source 104 may form part of the respiratory system 100 or may be provided separately to the respiratory system 100. In some embodiments, the flow source may include a plurality of separate components, some flow source components forming part of the respiratory system 100 and some components being provided separately to the system 100.

[0327] In the embodiment shown in Figure 1, the respiratory system 100 may include a flow source 104, a humidifier 108 for warming and humidifying the gas flow 106, an inspiratory conduit 110, conduit 114 (e.g. dry line or heated breathing tube), patient interface 112, one or more pressure relief valves (not shown), and a filter (not shown).

[0328] The flow source 104 may comprise an oxygen supply 120 such as an in-wall supply of oxygen, a tank of oxygen, a tank of other gas and/or a flow apparatus with a flow generator 122. Figure 1 shows a flow source 104 including a flow generator 122, an optional air inlet 124, and optional connection to an oxygen source (such as tank or 02 generator) 120 via a shut off valve and/or regulator and/or other gas flow controller 126, but this is just one option. The flow generator 122 can control flows delivered to the patient 102 using one or more valves, or optionally the flow generator 122 can comprise a blower (not shown) to facilitate movement of the gas flow 106. The flow source 104 may be one or a combination of a flow generator 122, oxygen source 120, air source 124 as described. The flow source 122 is shown as part of the respiratory system 100, although in the case of an external oxygen tank or in-wall source, it may be considered a separate component, in which case the respiratory system 100 has a connection port to connect to such a flow source. The flow source provides a flow of gas that can be delivered to a patient via an inspiratory conduit 110, and patient interface 112.

[0329] The patient interface 112 is disclosed in further detail elsewhere herein and may form part of a patient interface system which substantially seals with the patient's nose to substantially prevent outflow of gases except via at least one outflow vent provided in the patient interface system. The at least one outflow vent may be provided in a body portion of the patient interface 112, or in a conduit in fluid communication with the patient interface 112 through which gases leaving the patient interface 112 may travel to exit through the at least one outflow vent. In some embodiments, the patient interface 112 may comprise a nasal cannula with a body portion comprising a manifold and nasal prongs, and/or a nasal pillows mask, and/or a nasal mask, or any other suitable type of nasal patient interface. The flow source 104 may provide a gas flow rate of between, e.g. 0.5 litres per minute (LPM) and 375 litres per minute (LPM), or any range within that range, or even ranges with higher or lower limits, as previously described.

[0330] The flow source 104 is operable to provide the gas flow 106 at any suitable flow rate depending on requirements of the patient and/or relevant respiratory support required to be provided. The flow rate of the gas flow 106 can may be a continuous flow rate. In particular, the flow rate of the gas flow 106 may be a continuous flow rate independent of the patient's breathing. The continuous flow rate may be variable or generally constant.

[0331] A humidifier 108 may optionally be provided between the flow source 104 and the patient 102 to provide humidification of the gas flow 106. In some embodiments, a humidifier 108 may be provided as part of the flow source 104. For example, the flow generator 122 may include a built-in humidifier. Humidification of the gas flow 106 can allow the comfortable delivery of gas flow at low and/or high flow rates. Humidity in the delivered gas flow also prevents the patient's airway from drying out, thereby mitigating mucociliary damage, and reducing risk of laryngospasms. Humidity in the gas flow can also reduce risks associated with airway drying such as nose bleeding, aspiration (as a result of nose bleeding), and airway obstruction, swelling and bleeding. It can also reduce risk of a laryngoscope getting stuck to the skin of the patient in a dry airway, which can cause trauma to the patient. In some configurations the gas flow may be humidified to contain greater than 10 mg/L of water, or greater than 20 mg/L, or greater than 30 mg/L, or up to 44 mg/L. In some embodiments, the gas flow may be heated by a heater (not shown) to 21° C to 42° C, or 25° C to 40° C, or 31° C to 37° C, or about 31° C, or about 37° C. The heater may be incorporated into or provided with humidifier 108 such that the gas flow is substantially simultaneously humidified and warmed. [0332] One or more sensors 128, 130, 132, 134 such as flow rate, pressure, gas species, humidity, temperature or any other suitable sensors can be placed throughout the system 100 and/or at, on or near the patient 102. Alternatively, or additionally, sensors from which such parameters can be derived could be used. In addition, or alternatively, the sensors 128 to 134 can be one or more physiological sensors for sensing patient physiological parameters such as but not limited to, blood pressure, heart rate, oxygen saturation, partial pressure of oxygen in the blood (blood oxygen concentration), respiratory rate, end tidal carbon dioxide, partial pressure of carbon dioxide in the blood (blood CO2 concentration), transcutaneous CO2 concentration (TcCO2), transcutaneous 02 concentration (TcO2), expired CO2 concentration, blood oxygen saturation (SpO2), expired 02 concentration, blood glucose level and level of anaesthetic agent in the patient 102. Alternatively, or additionally, sensors from which such parameters can be derived could be used. Other patient sensors could comprise EEG sensors, EKG/ECG sensors, EMG sensors, torso bands to detect breathing, and any other suitable sensors. One or more of the sensors might form part of the respiratory system 100, or be external thereto, with the respiratory system 100 receiving inputs from any external sensors. The sensors can be configured for communication with a control device 138.

[0333] In the embodiment illustrated in Figure 1, a sensor 136 may be provided for measuring the one or more patient parameters at the patient 102. This can be placed on the patient interface 112, for example, to measure or otherwise allow determination of parameters such as pressure, flow rate, 02 concentration and CO2 concentration to name a few, at the patient's airway (e.g. inside or outside/proximate the mouth and/or nose and/or patient interface). The sensor 136 may measure/sample the parameter(s) proximate the patient's airway continuously/periodically so as to continuously monitor the parameter(s) at the patient's airway during operation of the system 100 to provide respiratory support to the patient 102. In some examples, a parameter of interest may be determined indirectly. For example, an indication of flow rate may be determined indirectly from a measure of interface pressure, when the resistance to flow of the patient interface is known, as can be ascertained in a test or calibration. Monitoring one or more parameters such as pressure, flow rate, 02 concentration and CO2 concentration at the patient's airway during operation of the system 100 may enable the system to determine a patient condition. Other examples that permit parameter sensing are described herein, for example with reference to Fig. 18.

[0334] The system 100 further includes a control device 138 configured for operative communication with the sensors 130 to 136 to receive input from the sensors to allow determination of the presence of one or more "patient conditions" of the patient 102 which may trigger operation of the system 100 to alter the respiratory support being provided. One such alteration may involve changing the supply flow rate of gases in the gas flow 106.

[0335] In the event that the control device 138 receives an input or determines by processing of sensor data an indication of a patient condition, the control device may control the supply flow rate to change (increase or decrease) the flow rate of gas flow 106, or may direct a user of the system 100 to do so, or to otherwise carry out the methods disclosed herein which need not involve a change (increase or decrease) in the supplied flow rate of gas. An indication of patient condition may indicate that the patient is receiving or has received anaesthesia, or is apnoeic or is at risk of becoming apnoeic. In some examples, an indication of patient condition may correspond to a patient state, or may correspond to a patient parameter value meeting a pre-defined threshold that may be indicative of a patient state. Patient parameters may comprise one or more of, but are not limited to: depth of sedation of the patient (as may be determined e.g. by a Bispectral Index (BIS) monitor; heart rate; EEG signal values; EKG/ECG signal values; EMG signal values; blood oxygen concentration; blood oxygen saturation (SpO2); expired oxygen concentration; blood CO2 concentration; transcutaneous CO2 concentration (TcCO2); expired CO2 concentration; and blood glucose level. The patient condition may comprise a condition selected from a group comprising but not limited to: lower or upper airway obstruction; soft palate obstruction; absence of spontaneous breathing; patient inspiratory demand not being met; the patient is or is at risk of becoming apnoeic; patient depth of desired sedation being met; and expiratory airway pressure is, or is approaching, a non-optimal threshold. Thus, the supply flow rate may be controlled to a second supply flow rate which may be a higher flow rate than the first supply flow rate, in response to a patient condition being indicated. In another embodiment, the supply flow rate may be controlled to a second supply flow rate which may be a lower flow rate than the first supply flow rate, in response to a patient condition being indicated. In some cases, the clinician or other user may control the flow of gas to alter the supply flow rate in the absence of an indication of a patient condition, e.g. based on clinical judgement or for other reasons.

[0336] Control device 138 may be in operative communication with a user interface 140 which may comprise a display device and input/output (I/O) elements such as buttons, dials and/or a touch screen, for receiving user inputs. User interface 140 may present one or more indicators for providing an indication of a patient condition, and/or presenting one or more parameters determined by the control device 138 from sensor data that are indicative of a patient condition. The one or more indicators may comprise any one or more of a sound indicator (e.g. buzzer, alarm), a light indicator (e.g. an LED light), a graph and numeric values. In addition, or alternatively, the control device 138 may generate an alphanumeric message, animation, video or other output for display on the display device of the user interface 140 and/or which may be announced audibly.

[0337] The user interface 140 may receive information from a user (e.g. clinician or patient) that can be used for controlling or determining oxygen concentration, anaesthetic gas agent, temperature or humidity requirements of the gas flow 106, and/or flow rate requirements of the gas flow 106. By way of non-limiting example, the user interface 140 may be used to receive manual user input controlling the flow rate of the gases to be provided to the patient (i.e. supply flow rate). Alternatively or additionally, respiratory system 100 may be configured such that the control device 138 can determine the flow rate of the gases to be provided to the patient based on inputs received from the user and/or via sensors providing input concerning identification of the patient's condition. Such patient conditions may include that the patient condition is pre-anaesthesia, for which a first supply flow rate may be provided during a pre-oxygenation phase, and/or that the patient is receiving or is under anaesthesia - which might include when the patient is apnoeic or when the patient is breathing - for which a second supply flow rate may be provided which may correspond to a higher flow rate than the first supply flow rate.

[0338] In some embodiments, the respiratory system 100 can be configured to provide high flow gas to a patient and adjust the parameters of the high flow gas (such as supply flow rate, exhaust gas flow rate, patient interface pressure, volume of gas, gas composition) delivered to the patient. [0339] Whilst Figure 1 illustrates a single control device 138, it is understood that the respiratory system may include one or more control devices, and/or be configured to interface with one or more control devices external to the respiratory system (e.g. through a network connection). Indeed, the control device 138 can also include one or more processors to control operations of the respiratory system 100 including, for example, determination of patient parameters from sensor signals, determination of the presence of a patient condition, and determination of the control for the respiratory support appropriate for the indicated patient condition.

[0340] The respiratory system 100 may be an integrated or a separate component-based arrangement, generally shown in the dotted box in Figure 1. In some configurations, the respiratory system may comprise a modular arrangement of components. Furthermore, the respiratory system may comprise some of the components shown, not necessarily all are essential. Also, the conduit and patient interface/patient interface system do not have to be part of the system 100 and could be separately supplied and used with the system for provision of the required respiratory support. Hereinafter it will be referred to as respiratory system 100, but this should not be considered limiting.

[0341] The respiratory system 100 may be used in a range of scenarios including, without limitation, pre-oxygenation during an anaesthetic procedure, during or after anaesthetic or sedative agents are administered to a patient during an anaesthetic procedure). Some applications comprise, for example, high flow respiratory support, high flow therapy, ventilation, and provision of high flow gas-flows in the operating room, ICU or emergency treatment rooms. The respiratory system 100 may be used during patient monitoring, therapy, respiratory support or supplemental oxygen delivery.

[0342] Fig. 2 is a flow chart showing schematically a method 200 of providing respiratory support to a patient during a medical procedure. The method may be performed using a system e.g. as described with reference to Fig. 1. The method 200 comprises, in a step 202 providing a gases flow to the patient via a patient interface system having at least one outflow vent. In a step 204 the method comprises controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate. In a step 206 the method comprises controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow through the at least one outflow vent at a second exhaust flow rate. Through operation of the method 200, a first predetermined resistance to flow (RTF) of the at least one outflow vent at the first exhaust flow rate is different than a second predetermined resistance to flow (RTF) of the at least one outflow vent at the second exhaust flow rate. In some examples, the first predetermined RTF of the at least one outflow vent at the first exhaust flow rate is less than a second predetermined RTF of the at least one outflow vent at the second exhaust flow rate. It is to be understood that in examples comprising more than one outflow vent, the term "exhaust flow rate" refers to the total exhaust flow rate through all of the outflow vents, and the term "resistance to flow" refers to the total resistance to flow arising from all of the outflow vents. The first and second supply flow rates may be about the same as the respective exhaust flow rates in some examples.

[0343] In some examples, the first predetermined RTF of the at least one outflow vent at the first exhaust flow rate may be in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l. The second predetermined RTF of the at least one outflow vent at the second exhaust flow rate may be in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin- 1 to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l. For a given exhaust flow rate, the RTF of the at least one outflow vent may be attributable to the size and/or shape of the at least one vent e.g. by the total cross sectional area of the vent/s as described in further detail below. Resistance to flow of the at least one outflow vent can be determined as the difference between the interface pressure and ambient pressure, divided by the exhaust flow rate. Relevantly, as discussed below there is a non-linear pressure-flow relationship of gases which is attributable to the size and/or shape of the at least one outflow vent. Therefore, since exhaust flow rate is a function of the supply flow rate of gases provided to the patient, the RTF of the at least one outflow vent having a given size and/or shape can be changed by controlling the flow rate of the gases flow provided to the patient interface system when in use. This does not require adjustment of the size and/or shape of the at least one vent itself. [0344] In some examples involving a restriction for generating uneven flows in a chamber of the patient interface as discussed below, it is to be understood that at least two outflow vents should be provided, one provided for exit of flows from the chamber on each side of the restriction. In such an arrangement, the interface pressure on each side within the chamber (i.e. on each side of the restriction) approximates the pressure in the respective nare of the patient and the average of these pressures may represent the patient pressure within the nasal cavity (in the absence of net flows to or from the patient).

[0345] The patient interface as described elsewhere herein may comprise a sealing element. The sealing element can substantially prevent escape of gas from the patient except via the at least one outflow vent provided in the patient interface system. The patient interface system may comprise a patient interface 112 and an inspiratory conduit 110 providing a gases flow path for provision of a gases flow to the patient. The at least one outflow vent may be provided in the patient interface 112, and/or the at least one outflow vent may be provided as part of the inspiratory conduit through which expired gases from the patient may exit the patient interface system. The method may comprise the step of applying the patient interface to the patient in a step 201.

[0346] Fig. 3 is a flow chart showing schematically a method 300 of providing respiratory support to a patient during a medical procedure. Said method may be performed using a system e.g. as described with reference to Fig. 1. The method comprises, in a step 302, providing a gases flow to the patient via a patient interface system having at least one outflow vent. In a step 304 the method comprises controlling the gases flow at a first supply flow rate and generating a first interface pressure (PINTERFACE) and an exhaust flow through the at least one outflow vent at a first exhaust flow rate (EFR). In a step 306 the method comprises controlling the gases flow at a second supply flow rate and generating a second interface pressure (PiNTERFACE)and an exhaust flow rate (EFR) through the at least one outflow vent at a second exhaust flow rate. Owing to the non-linear relationship between interface pressure and exhaust flow rate, a second rate of change (RoC) in the second interface pressure (PINTERFACE) associated with the second exhaust flow rate (EFR) is greater than a first rate of change (RoC) in the first interface pressure (PiNTERFACE)associated with the first exhaust flow rate (EFR). In use, this may be observed as a higher RTF at higher flow rates. RoC may be determined for the patient interface using a simulation or test protocol as discussed below. The RoC may be an instantaneous RoC value, or an average value measured over e.g. a first range of exhaust flow rate values which includes the first exhaust flow rate, and e.g. a second range of exhaust flow rate values which includes the second exhaust flow rate. The method may comprise the step of applying the patient interface to the patient in a step 301.

[0347] Figs 2 and 3 show the steps 204/304 and 206/306 in an order comprising controlling the gases flow at the first supply flow rate before the second supply flow rate. However that need not be the case and the method may be varied such that step 206/306 comprising controlling the gases flow at the second supply flow rate occurs before step 204/304 comprising controlling the first supply flow rate, as shown by arrows in broken lines.

[0348] In some examples, the second supply flow rate is higher than the first supply flow rate. In some examples, the second interface pressure and the second exhaust flow rate are also higher than the first interface pressure and the first exhaust flow rate. This may be the case in application of the method 200, 300 in provision of respiratory support in a patient during introduction of anaesthesia, wherein the first supply flow rate is provided to preoxygenate the patient and once the patient has been delivered anaesthetic drugs, the second supply flow rate, being a higher flow rate, is provided to support the patient's oxygenation requirements. The first supply flow rate may be greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, or about 50 LPM, or higher such as about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM, about 100, about 110 LPM, about 120 LPM, about 130 LPM, about 140 LPM, or about 150 LPM or a value in between. The second supply flow rate may be greater than about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM or higher such as about 110 LPM, about 120 LPM, about 130 LPM, about 140 LPM, or about 150 LPM or a value in between. In some examples, the second supply flow rate may be less than 40 LPM such as about 20 LPM or about 30 LPM or a value in between.

[0349] In some examples, the first exhaust flow rate may be the same as the first supply flow rate. In some examples, the second exhaust flow rate may be the same as the second supply flow rate. In some examples, the first exhaust flow rate may be between more than about 0 LPM to about 40 LPM, or between more than about 0 LPM to about 30 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM. In some examples, the second exhaust flow rate may be between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM. The first and second (and third) supply flow rates may be about the same as the respective exhaust flow rate in some examples.

[0350] In some embodiments the method comprises providing the second supply flow rate in response to an indication of a patient condition. The indication of the patient condition may be determined in a step 205/305 by one or more of: observation of the patient and/or patient parameters e.g. by a clinician; user confirmation of administration of therapy to the patient e.g. by provision of an input to user interface 140; measurement of one or more patient parameters e.g. by sensors forming part of system 100 or sensors external to the system from which the values can be manually supplied via user interface 140; a control device using data received from a user or one or more devices, e.g. sensors monitoring patient parameters to determine the indication of the patient condition; and the patient self-describing their condition and either providing an input via user interface 140 or requesting a user or carer to do so.

[0351] In a system providing the method 200/300, the indication of patient condition may be provided to the control device 138 by a user interacting with user interface 140. Alternatively or additionally, the patient condition may be determined by a processor of the control device 138 which is programmed with pre-defined threshold values of one or more patient parameters, e.g. in a look up table or function stored in memory associated with the control device 138, which when compared with data received from sensor signals providing inputs to the control device, can be used to indicate the presence of a patient condition. Thus, the patient condition may correspond to a patient state, or may correspond to a patient parameter value meeting a pre-defined threshold that may be indicative of a patient state. Patient parameters may comprise one or more of, but are not limited to: depth of sedation of the patient (as may be determined e.g. by a BIS monitor); heart rate; EEG signal values; EKG/ECG signal values; EMG signal values; blood oxygen concentration; blood oxygen saturation (SpO2); expired oxygen concentration; blood CO2 concentration; transcutaneous CO2 concentration (TcCO2); transcutaneous 02 concentration (TcO2); expired CO2 concentration; and blood glucose level. The patient condition may comprise a condition selected from a group comprising but not limited to: lower or upper airway obstruction; soft palate obstruction; absence of spontaneous breathing; patient inspiratory demand not being met; the patient is or is at risk of becoming apnoeic; patient depth of sedation being met; and expiratory airway pressure is, or is approaching, a non-optimal threshold. Thus, the second supply flow rate which may be a higher flow rate than the first supply flow rate, may be supplied in response to a patient condition being indicated.

[0352] Control of the first and/or second supply flow rate may be achieved by one or more of: manual selection by a user of the second supply flow rate in response to the user (or the system which may comprise suitable sensors as described above) confirming the indication of the patient condition, e.g. in a system where the control device comprises a control knob on a flow source. In some embodiments, control is achieved by a controller such as control device 138 in Fig. 1 controlling to a user selected or predetermined second supply flow rate, or determining the second supply flow rate, e.g. by a processor associated with the control device, when the control device receives a user input confirming the indication of the patient condition. In some embodiments, control is achieved by a controller such as control device 138 in Fig. 1 determining the second supply flow rate when the control device determines, e.g. by a processor associated with the control device, the existence of the patient condition using data received from one or more devices e.g. sensors, monitoring patient condition parameters.

[0353] In some embodiments, the first supply flow rate may be provided before delivery of an anaesthetic agent to the patient, the second supply flow rate may be provided after delivery of an anaesthetic agent to the patient. Thus, the second supply flow rate may be provided in response to an indication that an anaesthetic agent is being or has been delivered to the patient. An indication that an anaesthetic agent is being or has been delivered to the patient may be determined by clinician observation of the patient and/or patient parameters and manual entry of the indication to a control device 138 using user interface 140. In some embodiments, control device 138 may use data received from a user or from one or more devices (e.g. sensors or a BIS) that provide an indication of an anaesthetic agent being or having been delivered to the patient. [0354] In some embodiments, the respiratory support is provided to the patient according to the methods 200 or 300 prior to anaesthetic agent delivery and/or prior to onset of anaesthesia or sedation in the patient. For example, the first and second supply flow rates may be provided to the patient during the pre-oxygenation phase prior to introduction of anaesthesia. For example, if it is determined that the patient has an obstructing soft palate. An advantage of the present disclosure when compared with conventional NHF arises from higher interface pressure generated at the second exhaust flow rate ranges, (which in turn generates a higher nasal cavity pressure) which may assist with clearing a soft palate obstruction that cannot be overcome with conventional NHF. A proxy for pressure in the nasal cavity may be determined by measuring patient interface pressure in a substantially sealed nasal interface.

[0355] In some embodiments, the method 200 comprises in a step 210 controlling the gases flow at a third supply flow rate and generating a third interface pressure (PINTERFACE) and an exhaust flow through the at least one outflow vent at a third exhaust flow rate (EFR), wherein a third predetermined resistance to flow (RTF) of the at least one outflow vent at the third exhaust flow rate (EFR) is different than the second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

[0356] In some embodiments, the method 300 comprises in a step 310 controlling the gases flow at a third supply flow rate and generating a third interface pressure (PINTERFACE) and an exhaust flow through the at least one outflow vent at a third exhaust flow rate (EFR), wherein a rate of change (RoC) in the third interface pressure (PINTERFACE) associated with a change in the third exhaust flow rate (EFR) is less than a rate of change (RoC) in the second interface pressure (PINTERFACE) associated with a change in the second exhaust flow rate (EFR).

[0357] The third supply flow rate may be lower than the second supply flow rate, e.g. when the patient condition has changed. Accordingly, the third interface pressure, the third EFR, the third predetermined RTF, and the RoC in the third interface pressure associated with a change in the third EFR, may all be lower than those at the second supply flow rate. The third supply flow rate, the third interface pressure, the third EFR, and the third predetermined RTF, may all be the same as the respective first supply flow rate, first interface pressure, first EFR, and first predetermined RTF. The third supply flow rate may be higher than the second supply flow rate e.g. if the patient condition remains. Accordingly, the third interface pressure, the third EFR, the third predetermined RTF, and the RoC in the third interface pressure associated with a change in the third EFR, may all be higher than those at the second supply flow rate.

[0358] Thus, in some embodiments, the method comprises providing the third supply flow rate which may be provided in response to an indication of a different (second) patient condition to the previously identified (first) patient condition. The indication of the second patient condition may be determined in a step 209/309 by one or more of: observation of the patient and/or patient parameters; measurement of one or more patient parameters e.g. by sensors forming part of system 100 or sensors external to the system from which the values can be manually supplied via user interface 140; a control device using data received from a user or one or more devices (e.g. sensors) monitoring patient parameters to determine the indication of the different patient condition; and the patient self-describing their condition and either providing an input via user interface 140 or requesting a user or carer to do so. The method need not continue to provide the third supply flow rate indefinitely. The method may comprise changing the control from the third supply flow rate to the first supply flow rate or to the second supply flow rate.

[0359] In a system providing the method 200/300, the indication of the second condition may be provided to the control device 138 by a user interacting with user interface 140. Alternatively or additionally, the second patient condition may be determined by a processor of the control device 138 which is programmed with pre-defined threshold values of one or more patient parameters, e.g. in a look up table or function stored in memory associated with the control device 138, which when compared with data received from sensor signals providing inputs to the control device, can be used to indicate the presence of the second patient condition. Thus, the second patient condition may correspond to a patient state, or may correspond to a patient parameter value meeting a pre-defined threshold that may be indicative of a patient state. The second patient condition may be selected from a group comprising e.g. lower or upper airway becoming patent; soft palate is no longer obstructing; presence of spontaneous breathing; patient inspiratory demand being met; predetermined level of alertness being met; and expiratory interface pressure meets or exceeds an optimal threshold. These conditions may indicate arousal or emergence from anaesthesia or apnoea. [0360] In some embodiments, the exhaust flow rate and interface pressure are related such that as the exhaust flow rate increases, the rate of change of interface pressure increases, particularly at higher exhaust flow rates. In use, for a given supply flow rate of gases, this can result in an interface pressure that is higher than is generated in conventional NHF (using a non-sealing interface), particularly at higher exhaust flow rates. This can provide certain advantages as will be discussed below. In some embodiments, the exhaust flow rate (Q) and interface pressure (P) may be related such that when presented graphically, they demonstrate a non-linear relationship. In some embodiments, the non-linear relationship is a relationship which may be referred to as a PQ profile. A PQ profile may comprise a polynomial component. In some embodiments, the polynomial component may be of degree two (quadratic). An example of a PQ profile according to embodiments of the disclosure is illustrated at 402 in Fig. 4.

[0361] Exhaust flow rate is a function of the supply flow rate of gases provided to the patient. The first and second (and third) supply flow rates may be about the same as the respective exhaust flow rate in some examples. Therefore increasing the supply flow rate can increase the exhaust flow rate. Exhaust flow rate may also be affected by patient-dependent flows e.g. inspiratory and expiratory flow rate of the patient, and whether the patient's mouth is opened or closed. The PQ profile in Fig. 4 is therefore representative of the relationship between interface pressure and exhaust flow rate in the absence of net flows to or from the patient, e.g. during a breath hold, or a transition between inspiration and expiration, or in an apnoeic situation. The curved PQ profile in Fig. 4 may be time-averaged and/or the interface pressure may represent the mean interface pressure over several patient breathing cycles. There may be some variation in the PQ profile 402 attributable to component variability or sensor measurement variability. As shown, the curved PQ profile 402 is represented as a single line rather than a band, and may represent instantaneous or a mean, median, or average of the values of pressure.

[0362] A PQ profile such as curve 402 or values representing the relationship between interface pressure and exhaust flow rate may be obtained by performing a simulation or test protocol using a patient interface of the type required for the respiratory support. In such a test, the nasal elements of the patient interface are sealed to simulate the patient in the absence of net flows to and from the patient. Interface pressure is measured across a range of supply flow rates. The range of supply flow rates may include at least the first supply flow rate and/or the second supply flow rate and/or the third supply flow rate according to the methods of providing respiratory support. Since there is no patient, the exhaust flow rate (e.g. the first exhaust flow rate and the second exhaust flow rate or the third exhaust flow rate) will be the same as the supply flow rate (e.g. the first supply flow rate and the second supply flow rate and the third supply flow rate, respectively). Furthermore, the measured interface pressure values (including the first interface pressure and the second interface pressure measured for the first exhaust flow rate and the second exhaust flow rate respectively, and optionally the third interface pressure measured for the third exhaust flow rate) can be used to generate a PQ profile curve, table or function. Resistance to flow of the at least one outflow vent can be determined as the difference between the interface pressure and ambient pressure, divided by the exhaust flow rate. Using the values from the simulation, the total RTF of the at least one outflow vent in the patient interface can be determined for a range of exhaust flow rates.

[0363] Furthermore, this simulation or test can be used to ascertain if the patient interface exhibits a certain rate of change of interface pressure (dP) with changes in exhaust flow rate (dQ) across the range of supplied flow rates. Using values obtained from the simulation or test, the dP/dQ can be calculated as a continuous function and then used to determine instantaneous values at one or more specific flow rates. For example, the instantaneous rate of change may be determined e.g. by calculating the gradient of a tangent to the PQ profile function at a given exhaust flow rate (e.g. the first exhaust flow rate and the second exhaust flow rate). Alternatively the rate of change may be determined as an average rate of change across a range of exhaust flow rate values which include e.g. the first exhaust flow rate or the second exhaust flow rate. Using such a simulation or test it is possible to determine if the respiratory support provided using the patient interface has at least one outflow vent configured to achieve a RTF and rate of change of interface pressure which meets the criteria of the present disclosure.

[0364] In some examples, a second rate of change in the second interface pressure associated with the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate. This is represented in the PQ profile 402 which has a first rate of change in interface pressure in a first exhaust flow rate range A', and a second rate of change in interface pressure in a second exhaust flow rate range B'. The rate of change may be an average value determined over a range of exhaust flow rates (e.g. flow rate ranges A' and B' in Fig. 4) that includes the first exhaust flow rate value or the second exhaust flow rate value. The rate of change may be an instantaneous value determined for a given flow rate (e.g. flow rate A or B in Fig. 4). As can be seen in Fig. 4, the second rate of change at B' is greater than the first rate of change at A'. Similarly, the second rate of change at B is greater than the first rate of change at A. As will be appreciated from Fig. 4, the rate of change of interface pressure is determined with respect to flow rate (not time). In some embodiments, the first rate of change may be in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l for a first exhaust flow value that is in a rate range of more than about 0 LPM to about 40 LPM, or more than about 0 LPM to about 30 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM. In some embodiments, the second rate of change may be in a range of greater than about 0.1 cmH2O/Lmin-l to less than about 0.6 cmH2O/Lmin-l, or about 0.15 cmH2O/Lmin-l to about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l for a second exhaust flow rate value that is in a range of more than about 30 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM. The first and second (and third) supply flow rates may be about the same as the respective exhaust flow rates in some examples.

[0365] The present disclosure can provide for provision of supply flow rates achieving high exhaust flow rates at safe patient pressures. This is discussed further in relation to Fig. 6. Utilising aspects of the present disclosure a clinician may achieve an interface pressure of about 3-5cmH2O at about 40 LPM exhaust flow rate and a higher interface pressure of about 10-12 cmH20 may be achieved at an exhaust flow rate of about 70 LPM which may be higher than an average patient airway pressure that can be achieved with conventional NHF at the same flow rate with the patient's mouth closed.

[0366] In some embodiments, this is achieved using a patient interface having at least one outflow vent and a sealing element. The sealing element can substantially limits escape of gases from the patient except via the at least one outflow vent. The exhaust flow rates and interface pressures disclosed herein may be achieved by providing a predetermined low resistance to flow (RTF) between the patient interface and the ambient environment (referred to herein as "ambient") which may be achieved by provision of the at least one outflow vent.

[0367] The predetermined RTF of the at least one outflow vent described herein may be beneficial in situations where the supplied flow rate is less than the patient's inspiratory demand, such that entrainment of ambient air to make up any deficit in inspiratory demand is made easier. That is, ambient air entering the patient interface through the outflow vents during inspiration may supplement the supplied flow. Due to the low RTF, pressure losses are reduced and work of inhalation may be reduced. With this in mind, while the terms "exhaust flow rate" and "outflow vent" are referred to throughout this disclosure, these do not define the flow direction of gases that may pass through the at least one outflow vent to be a direction from the patient to ambient. This is because a low RTF which permits a high exhaust flow rate can also permit inward flow from ambient to the patient with flow rates that may be the same as or similar to the above recited exhaust flow rates. Put simply, the flow across the at least one outflow vent may be in either direction.

[0368] In some examples, the method and/or system may comprise use of a patient interface having a RTF through the at least one outflow vent which is very low, such that the at least one outflow vent is generally permissive of flows in both directions in and out of the interface. In such examples, the total RTF of the at least one outflow vent may be between greater than about 0 cmH2O/Lmin-l to about 0.5 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin- 1 to about 0.4 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l, or between greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or between greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l. Supply flow rates may be greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, or about 50 LPM, or higher such as about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM, about 100, about 110 LPM, about 120 LPM, about 130 LPM, about 140 LPM, or about 150 LPM or a value in between. The supply flow rate may be about or the same as the exhaust flow rate, or higher.

[0369] By substantially removing the aforementioned uncontrolled leak path present in conventional NHF between the patient interface and ambient, the present disclosure provides a method that can provide more consistent performance over time and between patients. This may be achieved by substantially removing the uncontrolled leak between the nares and the patient interface such that gases exit the patient predominantly via the at least one outflow vent, wherein the at least one outflow vent is tuned such that the resistance to flow of the at least one outflow vent is higher at higher exhaust flow rates.

[0370] According to methods, systems and devices of the present disclosure, respiratory support can be provided to a patient undergoing a medical procedure, such as a scheduled medical procedure, where the patient has diminished respiratory function, is at risk of diminished respiratory function or is apnoeic. It is to be understood, however, that the present disclosure also has applications elsewhere in the hospital or healthcare environments, or other situations where respiratory support may be provided. The method may involve provision of respiratory support utilising the PQ profile of Fig. 4, controlling a supply flow rate to generate intended exhaust flow rates and interface pressures. Similar to conventional NHF, these methods and systems are flow rate controlled and can be utilised safely with existing gas sources in a manner that is familiar to clinicians. However, unlike conventional NHF, the methods and systems of the present disclosure may generate higher average interface pressures at higher flow rates, and potentially with lesser inter-patient pressure variations.

[0371] It is to be understood that the rate of change of the interface pressure with exhaust flow rate, according to embodiments of the present disclosure, need not be constant over a range of values of P or Q. The rate of change may comprise a PQ profile which in some embodiments, may comprise a polynomial component e.g. of degree two (quadratic). An example of a PQ profile according to embodiments of the disclosure is illustrated at 402 in Fig. 4. The rate of change may comprise an average rate of change over the operational flow rate range or pressure range, or over a sub-range of the operational ranges. An operational flow rate range or a sub-range of the operational ranges includes flow rate values at which respi ratory/cli nica I support is provided during use. The rate of change achieved by various examples disclosed herein may be determined using a simulation or test as described previously. For example, the first rate of change and/or the second rate of change may comprise an average rate of change. Furthermore, the relationship between P and Q for the first rate of change and the second rate of change may be such that when presented graphically, their relationship comprises one or more of: a stepwise change between the first rate of change and the second rate of change; a gradual change between the first rate of change and the second rate of change; a curvilinear change between the first rate of change and the second rate of change; a non-constant gradient in a portion of the first rate of change and/or the second rate of change; a non-step change at a transition between the first exhaust flow rate and the second exhaust flow rate; and a non-step change at a transition between the second exhaust flow rate and a third exhaust flow rate.

[0372] In some embodiments, the method comprises controlling the gases flow and generating one or more of: a first exhaust flow rate of about 40 LPM and a first interface pressure of about 3-5 cmH20, such as about 4 cm H2O; a first exhaust flow rate of about 30 LPM a first interface pressure of about 2-4 cmH20, such as about 3 cmH20; a second exhaust flow rate of about 50 LPM and a second interface pressure of about 5-8 cmH20, such as about 6 cm H2O; a second exhaust flow rate of about 55 LPM and a second interface pressure of about 6-8 cmH20; a second exhaust flow rate of about 60 LPM and a second interface pressure of about 7-9 cmH20; and a second exhaust flow rate of about 70 LPM and a second interface pressure of about 7-15 cmH20, such as about 9-12 cmH20, such as about 9-10 cm H2O or about 10-12 cmH20. The first and second (and third) supply flow rates may be about the same as the respective exhaust flow rate in some examples.

[0373] The method may comprise operating a flow source 104 to provide the gases flow, wherein the flow source is controlled by a control device 138 configured to receive user supplied control inputs received via user interface 140 and/or processor generated control inputs generated by a processor comprising part of or in operational communication with control device 138.

[0374] It will be appreciated that measured interface pressures may be affected if the patient's mouth is open. For example, at a given supply flow rate, the interface pressure that can be measured when the mouth is closed is greater than the interface pressure that can be measured when the mouth is open. Unlike conventional NHF, the interface pressures generated according to the present disclosure may be more consistent between patients and may generate higher pressures in the nasal cavity at higher exhaust flow rates. This can help overcome soft palate closure even if the central airway pressure subsequently remains low due to the mouth being open. Fig. 18 shows a patient interface having at least one sampling port which may be used for measuring interface pressure. Alternatively or additionally, interface pressure may be derived or estimated from system pressure as discussed below.

[0375] In some embodiments, the patient may be undergoing a medical procedure during provision of the respiratory support, such as a scheduled medical procedure. The method may comprise providing anaesthetic agent(s) to the patient. The patient may be spontaneously breathing during at least a portion of the medical procedure but may be made unconscious or sedated (as opposed to falling into a state of natural sleep or drowsiness) after provision of anaesthetic agent(s). The patient may be non-spontaneously breathing during at least a portion of the medical procedure after provision of anaesthetic agent(s). The patient need not be apnoeic during the medical procedure. The gases flow provided at one or both of the first supply flow rate and the second supply flow rate may comprise 100% 02 concentration although that need not be the case and the gases flow may comprise a blend of gases such as air and 02 or a blend of other respiratory gases.

[0376] Fig. 5 is a flow chart showing schematically a method 500 of providing respiratory support to a patient. The method may be performed using a system e.g. as described with reference to Fig. 1. The method 500 comprises, in a step 502, providing a gases flow to the patient via a patient interface system comprising at least one outflow vent and a sealing element. The sealing element can substantially limit escape of gases from the patient except via the at least one outflow vent. In a step 504, the method comprises controlling a supply flow rate of the gases to the patient interface system and generating an interface pressure (PINTERFACE) and an exhaust flow through the at least one outflow vent at an exhaust flow rate (EFR). Through operation of the method 500, the interface pressure (PINTERFACE) and the exhaust flow rate (EFR) comprise a non-linear relationship. The non-linear relationship may comprise a polynomial component e.g. of degree two, such as the PQ profile 402 of Fig. 4. [0377] It is to be understood that the non-linear relationship need not be entirely curvilinear. The non-linear relationship between the interface pressure and the exhaust flow rate may be related such that when presented graphically, the rate of change between interface pressure and exhaust flow rate comprises one or more of: a stepwise change between a first rate of change and a second rate of change; a gradual change between a first rate of change and a second rate of change; a curvilinear change between a first rate of change and a second rate of change; a non-constant gradient in a portion of the first rate of change and/or a second rate of change; a non-step change at a transition between the first exhaust flow rate and a second exhaust flow rate; a non-step change at a transition between the second exhaust flow rate and a third exhaust flow rate. The rates of change represented in the non-linear relationship need not be constant.

[0378] The first rate of change between interface pressure and exhaust flow rate may be in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l for a first exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM. The second rate of change of interface pressure and exhaust flow rate may be in a range of greater than about 0.1 cmH20/Lmin-l to less than about 0.6 cmH20/Lmin-l, or about 0.15 cmH20/Lmin- 1 to about 0.5 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.4 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.3 cmH20/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

[0379] Controlling the supply flow rate at step 504 may comprise controlling the gases flow and generating an interface pressure according to an exhaust flow rate-interface pressure relationship comprising one or more values selected from a group comprising but not limited to: a first exhaust flow rate of about 40 LPM and a first interface pressure of about 3-5 cmH20, such as about 4 cm H2O; a first exhaust flow rate of about 30 LPM a first interface pressure of about 2-4 cmH20, such as about 3 cmH20; a second exhaust flow rate of about 50 LPM and a second interface pressure of about 5-8 cmH20, such as about 6 cmH20; a second exhaust flow rate of about 55 LPM and a second interface pressure of about 6-8 cmH20; a second exhaust flow rate of about 60 LPM and a second interface pressure of about 7-9 cmH2O; and a second exhaust flow rate of about 70 LPM and a second interface pressure of about 7-15 cmH2O, such as about 9-12 cmH20, such as about 9-10 cm H2O or about 10-12 cmH20. The first and second supply flow rates may be about the same as the respective exhaust flow rate in some examples.

[0380] In some examples, the first exhaust flow rate may be between more than about 0 LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM. In some examples, the second exhaust flow rate may be between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM. The first and second supply flow rates may be about the same as the respective exhaust flow rates in some examples.

[0381] As disclosed in relation to other aspects herein, exhaust flow rate is a function of the supply flow rate of gases provided to the patient. A first supply flow rate may be provided and may generate a first exhaust flow rate and a first interface pressure, and a second (or subsequent) supply flow rate may be provided and may generate a second (or subsequent) exhaust flow rate and a second (or subsequent) interface pressure, wherein a graphical representation of the interface pressure and exhaust flow rate values is non-linear. In some examples, the non-linear graphical representation comprises a polynomial component. The non-linear graphical representation may be determined according to a simulation or test as described herein. The first and second supply flow rates may comprise ranges as disclosed elsewhere herein, and may be selected for provision of respiratory support e.g. in response to an indication of a patient condition as disclosed elsewhere herein.

[0382] The patient interface system may comprise a patient interface as described elsewhere herein. In some embodiments the method comprises applying the patient interface to the patient in a step 501. The patient interface may be configured to provide the gases flow into the patient's nares, and may comprise a body portion comprising at least one outflow vent configured to generate a predetermined interface pressure due to the exhaust flow rate out of the at least one outflow vent which is a function of the supply flow rate. In some embodiments, the patient interface may comprise a body portion comprising at least one outflow vent configured to generate a first resistance to flow at a first supply flow rate which is different than a second resistance to flow at a second supply flow rate as described above. In some embodiments, the patient interface may comprise a pair of nasal prongs configured to provide the gases flow into the nares of the patient, and the at least one outflow vent comprises at least one opening in an insert located in each nare around the nasal prong. In such examples, the inserts comprise the sealing element as will be described elsewhere herein, as well as the at least one outflow vents. In some embodiments, the patient interface may comprise a pair of nasal prongs configured to provide the gases flow into the nares of the patient, and the at least one outflow vent comprises at least one opening in a sealing body formed around each nasal prong.

[0383] Fig. 6 is a graphical representation of interface pressures and exhaust flow rates as may be generated according to methods of the present disclosure in which the at least one outflow vent has a low total RTF and may be considered to be "permissive" (darker curve, 602) as compared to interface pressures and exhaust flow rates in restrictive systems (lighter curve, 604) having restrictive bias flow vents with higher total RTF. As disclosed elsewhere, exhaust flow rates (Qexhaust) generated according to the present disclosure are a function of the supply flow rate of gases provided to the patient. Therefore, Qexhaust is a function of a supply flow rate ( set). Owing to the patient interface system comprising at least one outflow vent and a sealing element that substantially limits escape of gases from the patient except via the at least one outflow vent, there is an expected interface pressure (Pexpc) at Qset. In situations where the patient is apnoeic, during a breath hold or in between inspiration and expiration, and when the patient's mouth is closed (i.e. in the absence of flows in or out of the patient), Qexhaust is equal to Qset as illustrated in Fig. 6. This is also the case in a simulation or test as disclosed herein. Actual interface pressures (Pactual) in use may vary between a minimum patient pressure (P_min) and a maximum patient pressure (Pmax) during the respiratory cycle of a spontaneously (or otherwise) breathing patient, and Qexhaust changes along the dark arrow. For example, P_max may be a pressure that is reached at the patient's peak expiratory flow rate. Pactual therefore varies about P_eXpc in a spontaneously breathing patient. As can be seen in Fig. 6, the permissive system represented by curve 602 can advantageously allow higher flow rates than the restrictive system represented by curve

604 without exceeding PUL.

[0384] As would be understood by one of skill in the art, the flow-controlled methods disclosed herein may involve use of system 100 which may be configured to operate in a predefined range of pressures. In some examples, this may be achieved e.g. by programming the control device 138 to provide respiratory support between a desired lower pressure limit PLL and upper pressure limit PUL. In one example, PLL may be 0 cmHzO. In another example, the control device 138 may be programmed to set PLL at about lcmHzO and PUL at about 12cmH2O. PUL and PLL may apply across a supply flow rate range of about 0 to 100 LPM. One or more pressure relief valves may be provided in system 100 to relieve pressure from the flow path in the event that sensors determine that the interface pressure has exceeded PUL. Alternatively or additionally the control device 138 may be programmed to control operation of the flow source 104 to reduce flows to the patient. This allows the method and system to operate at safe P_expc at Qset (since Qexhaust and Pactual are a function of Qset) that exceed peak inspiratory demand of the patient. In an apnoeic patient, there is no or little inspiratory demand (for example a flow resulting from gaseous exchange within the lungs) therefore Qset may be higher than 0 L/min or may be higher than the peak inspiratory demand of an average patient (e.g. 20-30 L/min), for example, for Q_set of 40 L/min, P_eXpc may be about 4cmH2O, or for set of 70 L/min, P_eXp_C may be between about 9-12 cml-hO.

[0385] Advantageously, the present systems also allows for provision of respiratory support for a range of adequate and/or safe Pactual at typical patient flow rates (Q_patient) of a spontaneously breathing patient, since Qexhaust and Pactual are functions of both Qset and the variable Qpatient due to patient flows e.g. respiration. For example, in a patient whose mouth is closed, for a Qset of 40 L/min and peak exhalation Qpatient of 30 L/min, the combined Qexhaust is about 70 L/min and P_max may be about 8 cml-hO. In another example in a patient whose mouth is closed, for a Qset of 70 L/min and peak exhalation Qpatient of 30 L/min, the combined Qexhaust is about 100 L/min, and P_max may be about 15 cml-hO.

[0386] Configuring the system 100 to operate between a pressure lower limit (PLL) and a pressure upper limit (PUL), may provide constraints on allowable patient pressure ranges, to avoid scenarios that may risk patient safety. These pressure limits may be programmed into the control device 138 such that when the control device receives a sensor signal indicating that the supply flow rate or the patient flow rate is too high, a pressure relief valve or other mechanism is actuated to remove pressure from the patient interface until the monitored pressure is within the pre-programmed range. For example if Qset and/or Q_patient are too high, Pactual may either exceed or not achieve some safe or desired level. PUL may therefore define a maximum safety or comfort pressure limit which is generally at a level above P_max to, for example, prevent harm to the patient and/or avoid gastric insufflation. If PUL is exceeded, safety procedures may be triggered in the system to avoid harm to the patient. This may involve the system actuating a pressure relieve valve and/or pressure sensing flow controller and/or shutting down the flow source 104, and/or reducing the control value for the supply flow rate.

[0387] In some examples, system 100 may be configured such that control device 138 allows Pactual to deviate from PLL and PUL by a tolerable amount over a respiratory cycle. Thus in some examples, system 100 may utilise system pressure sensors to detect when a Pactual falls outside the range of PLL and PUL, such that control device 138 is programmed to respond by altering Qset momentarily to cause Pactual to return to within the range of PUL and PLL. Scenarios where this may be advantageous comprise e.g. occurrence of a rapid inhale as illustrated in the graph of Fig. 7. A rapid inhale could cause Pactual to drop below PLL in which case the control device 138 could momentarily adjust Qset to push Pactual to at least PLL as shown.

[0388] Embodiments of the disclosure comprise or may be provided using a patient interface which can be applied to the patient to provide a flow of gases to the patient for provision of respiratory support as disclosed herein. The patient interface comprises a nasal delivery element such as a pair of nasal prongs or pillows for providing a flow of gases into the nasal cavity and at least one outflow vent which permits an exhaust flow of gases from the interior of the patient interface to the exterior of the patient interface. One or more sealing elements are provided. The one or more sealing elements can substantially prevent escape of an exhaust flow of gases from the patient (or from the patient interface), except via the at least one outflow vent. In some examples the one or more sealing elements may be additional (e.g. applied to) the nasal delivery element. In some examples the one or more sealing elements may be integrated with or form part of the nasal delivery element. The patient interface comprises a gases flow path that is couplable or in fluid communication with e.g. an inspiratory conduit 110 through which the flow of gases is received. The flow of gases is provided at a supply flow rate. As noted elsewhere herein, the exhaust flow rate is a function of the supply flow rate. The at least one outflow vent is configured, e.g. sized and/or shaped such that the exhaust flow of gases is generated at an intended interface pressure when gases are supplied to the patient interface at a predetermined supply flow rate e.g. in the absence of patient breathing. In such cases, the exhaust flow rate may substantially correspond to the supply flow rate. It is to be understood that the relationship between exhaust flow rate and interface pressure arising from the configuration of the at least one outflow vent may be described in this disclosure "in the absence of patient breathing". It is to be understood that this is not limited to situations where the patient is apnoeic, and is to be taken to also comprise e.g. during a breath hold or pause between inspiration and expiration while the patient's mouth is closed, or circumstances where relevant measures can be obtained without being impacted by the effect of breathing or flows to or from the patient's airway. For a test/simulation as described herein, this means while the nasal elements of the patient interface are sealed to simulate the patient in the absence of net flows to and from the patient.

[0389] The patient interface is configured, upon supply of a flow rate of gases which is controlled according to the methods disclosed herein, to generate an interface pressure during provision of the respiratory support. In some embodiments, the configuration of the at least one outflow vent is fixed. This may reduce variability of the respiratory support provided to the patient over time, and may reduce variability between patients. It is to be understood that the "exhaust flow rate" may comprise a range of flow rate values and corresponds to the total exhaust flow rate though all of the outflow vents when more than one is provided. In some embodiments, the at least one outflow vent is configured such that the interface pressure and exhaust flow rate generated by the patient interface during use comprise a non-linear relationship. Such relationship may be ascertained by plotting values of interface pressure and exhaust flow rate generated across a range of supply flow rates in the absence of patient breathing. The relationship may be obtained by performing a simulation or test protocol as described elsewhere herein. The protocol may be applied in reverse, to determine the configuration of the at least one outflow vent. For example, by deciding the required interface pressure values for a range of exhaust flow rate values (which, in a simulated environment are the same as the supply flow rate values) the required resistance to flow can be ascertained. This can be used to inform the total cross sectional area of the vent/s which in turn can be used to inform the size and/or shape of the vent/s.

[0390] In some examples, the non-linear relationship comprises (in part or in its entirety) a curvilinear relationship which may be referred to as a PQ profile. A PQ profile may comprise a polynomial component. In some embodiments, the polynomial component may be of degree two. An example of a PQ profile according to embodiments of the disclosure is illustrated at 402 in Fig. 4. Other PQ profiles are also contemplated within the scope of this disclosure. For example, the PQ profile may comprise a rate of change (of pressure P over a range of exhaust flow rates Q) that may or may not be constant over a range of values; the rate of change may comprise an average rate of change over the operational flow rate range or pressure range, or over a sub-range of the operational ranges. For example, the PQ profile or parts thereof may comprise an average rate of change. In some examples, the PQ profile may comprise one or more of: a stepwise change between the first rate of change and the second rate of change; a gradual change between a first rate of change and a second rate of change; a curvilinear change between a first rate of change and a second rate of change; a non-constant gradient in a portion of the first rate of change and/or the second rate of change; a non-step change at a transition between the first exhaust flow rate and the second exhaust flow rate; and a non-step change at a transition between the second exhaust flow rate and a third exhaust flow rate. The interface pressure P may comprise an average or mean interface pressure measured over a flow rate range.

[0391] In some examples, the patient interface is configured such that in use, the interface pressure and the exhaust flow rate through the at least one outflow vent comprises a non-linear relationship comprising a rate of change of the interface pressure in a range of more than 0.15 cmH2O/Lmin-l to less than 0.5 cmH2O/Lmin-l. In some examples, a first rate of change in the PQ profile may be in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l for a first exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM. In some examples, a second rate of change in the PQ profile may be in a range of greater than about 0.1 cmH20/Lmin-l to less than about 0.6 cmH20/Lmin-l, or about 0.15 cmH20/Lmin-l to about 0.5 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.4 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.3 cmH20/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM. A rate of change may comprise a mean or average rate of change. The supply flow rates may be about the same as the respective exhaust flow rates in some examples.

[0392] In some examples, the patient interface may comprise a nasal delivery element (such as a pair of nasal prongs) of a non-sealing patient interface and an insert that is placed within each of the patient's nasal passages. The insert may be configured to standardise a portion of the patient's nasal passages such that the insert together with the nasal delivery element may occupy substantially all of the patient's nasal passage, and the at least one outflow vent is provided in the insert.

[0393] For example, the patient interface may comprise at least one nasal element configured to provide the gases flow into a nare of the patient and the at least one outflow vent may comprise a gap defined between the nasal prong and an insert located in the nare. In other examples, the patient interface comprises at least one nasal prong configured to provide the gases flow into a nare of the patient and the at least one outflow vent comprises one or more openings in an insert locatable in the nare around the nasal prong. In such an arrangement, the insert comprises the sealing element and the at least one outflow vent.

[0394] An advantage of a patient interface comprising inserts may include ability to retrofit the inserts to existing non-sealing patient nasal interfaces that are not otherwise suitable for providing respiratory support as disclosed herein. Thus, an insert may be supplied together with a non-sealing patient nasal interface. Alternatively, an insert may be supplied e.g. in pairs as a separate product that can be supplied as an accessory for use with a nonsealing patient nasal interface. An insert may be applied over each of the prongs to standardise operation of the non-sealing patient nasal interface such that the inter-patient variability in exhaust flow around the nasal prongs is removed, and substantially replaced by at least one outflow vent provided in at least one insert, or an outflow vent formed between the prong and the insert, wherein the at least one outflow vent has a known configuration. The configuration is such that for predetermined supply flow rate the interface generates an intended exhaust flow rate and interface pressure. The intended exhaust flow rate (Q) and interface pressure (P) may be related according to a PQ profile.

[0395] In other examples, the patient interface comprises a pair of nasal prongs configured to provide the gases flow into one or both of the patient's nares, and the sealing element comprises at least one nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with or around the patient's nare. Thus the sealing element may be integrated with or into the gas delivery element that is inserted in or onto the patient's nares when in use. In some examples, the sealing element may also comprise at least one outflow vent in a manner similar to the insert described above. Alternatively or additionally, the patient interface may further comprise a body portion comprising the at least one outflow vent.

[0396] An example of a patient interface 520 according to embodiments of the disclosure is provided in Fig. 8 and Fig 18. The patient interface comprises a body portion 521 having outflow vents 530, and nasal pillows 522. In use, nasal pillows 522 are inserted onto the patient's nares to form a substantial seal with the nares so that gases from within the body portion 521 are delivered to the nasal airway, and gases from the nasal airway (which may comprise gases supplied to the patient as well as expired gases from the patient) can exit the nares and the patient interface to ambient via the outflow vents 530. Thus, the sealing nasal pillows 522 minimise unknown leaks between the patient interface 520 and the patient's nares. Minimising unknown leaks may minimise variability of interface pressures generated over time, and between different patients, for a given exhaust flow rate or range of exhaust flow rates. While nasal pillows 522 are provided in the example of Fig. 8, it is to be understood that other sealing elements may be provided as a substitute, such as e.g. sealing prongs, nasal cushions, cradles and the like. An example of sealing inserts 720 applied over nasal prongs 113 of a patient interface 112 is shown in Fig. 19. Here, the inserts 720 are provided with a plurality of outflow vents 730 through which gases (represented by broken lines) can exit the patient's nares. The outflow vents 730 may be provided around the entire circumference of the insert 710, or part thereof. The outflow vents may be arranged in a single row or in a plurality of rows or in some other pattern. Alternatively outflow vents 730 may be provided in a substantially randomised pattern. Arrows 106 represent the gas flow from nasal prongs 113 into the nares, when in use. It is to be understood that in some examples, the sealing inserts 720 may be formed integrally with the patient interface. For example, the function of a sealing insert 720 and a nasal prong 113 may be integrated forming sealing prong (not shown).

[0397] The example of Fig. 8 provides 6 outflow vents (best shown in Fig. 9) configured to generate, in use for a predetermined supply flow rate, an interface pressure (P) and an exhaust flow through the at least one outflow vent at an exhaust flow rate (Q); wherein the interface pressure and the exhaust flow rate comprise a non-linear relationship. However, it is to be understood that fewer than 6 or more than 6 outflow vents may be provided in some examples. The at least one outflow vents are configured, e.g. sized and/or shaped, to achieve a low RTF e.g. by the total cross-sectional area of the vent/s. It is to be understood that the low RTF may comprise the values of the first resistance to flow and/or the second first resistance to flow as disclosed herein. Thus a high exhaust flow rate may be generated at patient interface pressures that are safe at a supply flow rate that is commonly used in the provision of conventional HF respiratory support. The at least one outflow vents 530 may also be designed to achieve in use a particular pressure differential, or range of pressure differentials, between the patient interface 520 and ambient air at high supply flow rates (i.e. that are commonly used in conventional HF respiratory support). For example, the outflow vents 530 may be designed to achieve in use a pressure differential of about 7 cmH2O to about 15 cmH2O for an exhaust flow rate of 70 LPM (in the absence of net flows to or from the patient). The permissive nature of the at least one outflow vent (arising due to the low RTF) has a further advantage in that they may be utilised for provision of gases into, as well as out of, the patient interface body, e.g. during bag-masking, as described in further detail below.

[0398] In the examples of Figs 8, 9 and 14, the outflow vents 530 are provided in a vent member 531 facing outwardly from the patient when the patient interface 520 is applied to the patient. The vent member 531 may be comprised of a substantially rigid material such as a plastic or polymer material configured to form a friction fit or clip onto the main body portion 521 of the patient interface. The vent member 531 and body portion 521 may together define a chamber 532 as discussed below. In some embodiments, the vent member may also comprise one or more retention mechanisms 540 for connection of a headgear connector such as a head strap as shown in Figs 8 and 9. In other examples, there is no vent member and the outlet vents are formed or over moulded to the interface, or formed in the interface body such that the interface body comprising the vent/s is formed from a single unitary piece.

[0399] The at least one outflow vent 530 may also be configured to exhibit transitional or turbulent flow characteristics (e.g. Re > about 2000 to 3500) at high supply flow rates to achieve exhaust flow rate and interface pressures that align with a preferred PQ profile. At high supply flow rates such as above 50 LPM, the exhaust gases flow exiting the at least one outflow vent 530 may have transitional and/or turbulent flow characteristics which may achieve a greater pressure differential between the patient interface and ambient, that translates to higher interface pressure relative to conventional NHF (utilising a non-sealing nasal interface), contributing to the generation of exhaust flow rates and patient pressures which in use provide the rate of change performance comprising the non-linear profiles disclosed herein.

[0400] The at least one outflow vent 530 may also be configured to minimize condensate occlusion which may arise since gases provided to the patient and/or exhaled by the patient would likely have humidity levels that are higher than ambient air. In some examples, the at least one outflow vent 530 may be sized and/or shaped such that for a given pressure within the patient interface, capillary pressure of a condensate droplet is less than that interface pressure.

[0401] In some examples, the at least one outflow vent 530 may comprise a width dimension of about 3mm. For example, if the cross-sectional shape of the at least oneoutflow vent 530 is a circle, oval, or an ellipse, this dimension comprises a diameter and a major or minor axis respectively. Other cross-sectional shapes that may be suitable for the at least oneoutflow vent 530 comprise e.g. an obround, quadrilateral, or squircle to name a few. There may be 1, 2, 3, 4 or 5 outflow vents, or more such as 10, 15, 20, 25, 30, 35, 40, 45, 50 or considerably more such as 100, 150, 200 or more or any number in between. The outflow vents provided in a patient interface need not be of the same size or shape or cross sectional area. As mentioned, for a given exhaust flow rate, the RTF of the at least one outflow vent may be attributable to the size and/or shape of the at least one vent e.g. the total cross sectional area of the vent/s provided in the interface system. When more than one vent is provided, the RTF refers to the total RTF of all individual vents combined. The total cross sectional area of the vents may be in a range of about e.g. about 20 to about 100 mm² such as about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm². In some examples, the total cross sectional area of the vents may be in a range of about e.g. 35 mm² to about 50 mm² such as about 35 mm² to about 40 mm² or about 35 mm² to about 45 mm². In some non-limiting examples, the total cross sectional area of the at least one outflow vent may comprise about 42 mm² across about 6 openings of about 3 mm diameter each, or about 44 mm² across about 14 openings of about 2 mm diameter each, about 30 mm² across about 17 openings of about 1.5 mm diameter each, about 35 mm² across about 5 openings of about 3 mm diameter each. In some examples, the average cross sectional area for each opening comprising the at least one outflow vent comprises about 1.5 to 8 mm² such as about 7 mm² per opening, which may be an average, or between about 5 mm² and 8 mm². The low RTF of the at least one outflow vent 530 also facilitates bag-masking as discussed below. It is preferred that the at least one outflow vent 530 is non-variable (i.e. of fixed configuration) so as to limit performance variability over time and between patients.

[0402] When more than one outflow vent is provided, each of the two or more outflow vents need not be of the same size and/or shape. For example, a patient interface for provision of respiratory support, may comprise a gases flow path for provision of a gases flow to the patient, at least one outflow vent configured to permit an exhaust flow of gases and a sealing element (the sealing element can substantially prevent escape of gas from the patient except via the at least one outflow vent when in use and when the patient's mouth is closed), wherein the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. In some examples, the at least one outflow vent may comprise openings having at least two different sizes and/or shapes. In an example, the at least one outflow vent comprises at least one small opening and at least one large opening. The patient interface may be configured to generate an interface pressure during provision of the respiratory support.

[0403] In some examples, small openings may have a cross sectional diameter less than about 1mm or less than about 0.7mm. In some examples, small openings may have a cross- sectional diameter in a range of about 0.5 mm to about 0.7 mm, or about 0.5 mm to about 1 mm. There may be a plurality of small openings. In some examples, there may be 5 or 10 or 20 small openings, or there may be more or fewer small openings. The small openings may all have the same size and/or shape. On the other hand the small openings need not have the same size and/or shape.

In some examples, large openings have a cross sectional diameter greater than about 1mm or greater than about 2mm. In some examples, large openings may have a cross-sectional diameter in a range of about 1 mm to about 3 mm or about 2 mm to about 3 mm. There may be a plurality of large openings. There may be 1 or 2 or 3 or 4 or 5 large openings. When there is more than one large opening, they may all have the same size and/or shape. On the other hand the large openings need not have the same size and/or shape.

[0404] In some examples, the total cross-sectional area (CSA) of the small openings may be similar to the total cross-sectional area of the large openings. In some examples, about 50% of the total CSA of the at least one outflow vent may be attributable to the total CSA of the small openings and about 50% of the total CSA of the at least one outflow opening may be attributable to the total CSA of the large openings. In some examples, the total CSA of the small openings is within about 5%, or within about 2% of the total CSA of the large openings or vice versa. In another example, about 75% of the total CSA of the at least one outflow vent may be attributable to the total CSA of the small openings and about 25% of the total CSA of the at least one outflow opening may be attributable to the total CSA of the large openings. For example, Fig. 20 shows two large openings each of 2 mm diameter and fifty-four small openings each having 0.7 mm diameter resulting in a total CSA of 27 mm² of which about 78% is attributable to small openings.

[0405] Inclusion of small openings may allow some of the flow from the at least one outflow vent to be at lower Reynolds numbers so that the flow is more laminar through the small openings compared with more turbulent flow through the large openings. In some examples, large openings may be sized and/or shaped to achieve the desired non-linear relationship between interface pressure and exhaust flow rate (i.e. a PQ profile) as described elsewhere herein. Meanwhile small openings may be provided to achieve a therapeutic effect. In some examples a therapeutic effect may include a gas cloud effect due to the lower Reynolds numbers and laminar flow through the small openings. [0406] As shown in Fig. 20 there may be an order of magnitude more small openings 530A than large openings 530B in some examples. This may permit a sufficient portion of the exhaust flow to exit the small openings in order to contribute to a gas cloud effect.. In Fig. 20 there is a single row of small openings 530A extending substantially all the way around a front portion, or vent member 531, of the patient interface 520. A second row of small openings 530A may be provided on a portion of the vent member 531 which directs gas exiting the second row downwards as shown, i.e. towards the mouth when in use. The presence of the small holes may also reduce noise generated by exhaust flows exiting the patient interface due to their more laminar flow and/or a reduction in the amount of turbulent flow that would otherwise exit via a larger opening 530B. In one specific example that is represented in Fig. 20, there are two large openings each of 2 mm diameter and fifty- four small openings each having 0.7 mm diameter. Other arrangements are of course contemplated, with the at least one outflow vent comprising e.g. about 2 to about 5 large openings and about 30 to about 70 small openings. The small and/or large openings may be arranged on the patient interface 520 in a manner that is suitable for the clinical requirements.

[0407] The size range of the diameter of small openings may in some examples be between about 0.5 mm and about 1 mm, or about 0.5 mm to about 0.75 mm. As the diameter reduces, the interface pressure required to overcome the capillary pressure, should condensate form in the openings, becomes higher. Thus reducing the hole size further may not be beneficial.

[0408] In examples providing both large and small openings, it may be advantageous to direct flow from the large openings in a direction that is different from the direction of the flow from the small openings. This may, be particularly advantageous when it is desirable to create a region of low velocity exhaust flow via the small openings, i.e. a gas cloud effect as described above. Otherwise, the region of low velocity exhaust flow via the small openings could be disrupted by the higher velocity flows from the large openings if they are directed in the same or similar direction.

[0409] In an example as shown in Fig. 20, a larger number of small openings concentrated toward a particular region of the patient interface (or the patient's anatomy when in use) can create a diffuse cloud of the exhaust flow exiting the interface through those openings. In a particular but non-limiting example, there may be approximately 50 small e.g. substantially circular openings each having a diameter of about 0.7mm. In another example where the patient interface only comprises small openings (and no large openings) intending to achieve a gas cloud effect, there may be approximately 150 small openings and these may be substantially circular and may have a diameter of about 0.7mm.

[0410] The size and/or number of small and large openings may be selected or tuned to achieve a particular desired relationship between interface pressure and exhaust flow rate. The size and/or number of small and large openings may be selected or tuned to enable a particular fraction of the exhaust flow to exit each 'type' of opening. Since the resistance to flow of each opening is dependent upon exhaust flow rate, the number of openings of each size could be tuned to permit exit of a particular fraction of the exhaust flow for a given flow rate, e.g. tuned for a desired fraction at 50L/min or another specific given flow rate or range of flow rates.

[0411] In some examples, when in use, flows from the at least one large opening may be directed in a direction that is different from a direction of flows from the at least one small opening. In some examples, flows from the at least one small opening may be directed towards the patient's mouth. Directing of the flow of gas from a plurality (or all) of the small openings in a common direction (such as towards the mouth) may assist with creating a gas cloud effect in a desired location.

[0412] The small openings may be directed towards the mouth and the flow exiting the small openings has a lower velocity than flow exiting large openings. Due to the lower velocity, flow from the small openings can create a cloud of therapeutic gas around the mouth. This gas cloud effect may be beneficial when the patient is breathing with their mouth open and entraining gas through their oral cavity. The presence of a cloud of therapeutic gas in that region may provide the patient with an increased FiO2 compared to without the cloud.

[0413] In the examples above it may be desirable to direct flows from different types (or size) of openings in different directions. In other examples, it may be desirable that all flow from the at least one outflow vent is directed in a certain direction when in use. This may be different to the direction of exhaust gases exiting in the examples shown in Fig. 8, 9, 14 to 16 and 18, which show exhaust flows exiting the at least one outflow vent in a direction away from and substantially orthogonal to the patient's face when in use.

[0414] In one example, it may be desirable to direct substantially all the exhaust flow of gas from the at least one outflow vent towards the patient's mouth when in use, so that all therapeutic gas flow exiting the at least one outflow vent is directed towards the mouth. This may permit some of the therapeutic gas from the at least one outflow vent to be entrained by the patient should they be inspiring through their mouth. In some examples, the at least one outflow vent 530 may be located on a surface or edge of the patient interface 520, or on a surface or edge of a vent member 531, such that the at least one outflow vent is directed towards the patient's mouth when in use as shown in Fig. 21.

[0415] In another example, flows from the at least one large opening may be directed away from the patient's mouth. Thus, the at least one outflow vent 530 may be located on a surface or edge of the patient interface 520, or on a surface or edge of a vent member 531, such that the at least one outflow vent is directed away from the patient's mouth when in use as shown in Fig. 22. There may be clinical situations where directing the flow exiting the at least one outflow vent away from the patient's mouth, such as toward the patient's forehead may have benefits. One such situation may arise, if a clinician is working on the oral/nasal region of the patient and would prefer that flow from the at least one outflow vent is not directed to towards them, or their clinical access area. Directing the flow towards the patient's forehead may also reduce the amount of oxygen flow around the patient's head and neck region in some scenarios.

[0416] In some examples, the patient interface may comprise an access port. The access port may be normally closed so as to permit generation of an interface pressure during provision of the respiratory support using the patient interface. However the access port may be utilised should a clinician require access to the nasal cavity during therapy. For example, if the clinician wishes to insert a naso-gastric (NG) tube or insert an instrument via the nasal cavity, or insert a gas sampling conduit through the access port.

[0417] The access port may comprise a duckbill valve or a one-way valve that is normally closed but which is openable to allow access to the interface to permit insertion of e.g. smaller tubes or tools to access the nasal cavity. An example is provided in Figs 23 and 24 which show part of patient interface 520 corresponding to Figs 15 and 16 which has been modified to include an access port 539 and valve members 537. In Fig. 23 the valve members 537 are in a closed arrangement such that gases do not exit from chamber 532 via the access port 539 during use of the patient interface to provide respiratory support. In Fig. 24, a NG 720 tube is inserted via the access port 537, pushing against the valve members 539 moving them into an open arrangement. To enter the nasal cavity the NG tube 720 is inserted through the chamber 532 and nasal pillows 522. Upon removal of the NG tube 720 from the access port 537, the valve members return to the normally closed arrangement. In some examples, the valve members 537 may be somewhat compliant so as to form a substantial seal around a tube or that has been inserted so that respiratory support may continue to be provided while the access port 537 is used.

[0418] In another example, the access port may comprise an opening that is formed when the vent member 531 which contains the at least one outflow vent 530 is removed from the patient interface 520. Such an access opening may be larger than the access opening of Figs 23 and 24. An example is illustrated in Fig. 25 which shows the access opening 537 into which a NG tube 720 has been inserted. The vent member 531 may comprise a friction or clip-on fitment with the body portion 521 of the patient interface 520. In some embodiments it may be preferred that a tool is not required for removal of the vent member 531 from the body portion 521 of the patient interface. Thus in some examples, one or both of the body portion 521 and the removable vent member 531 may comprise a feature such as a tab (not shown) to assist with removal of the vent member to reveal the access port 537 so that a tool is not required. A seal or gasket may be provided on one or both of the vent member 531 and the body portion 521 so as to ensure that gas does not exit the patient interface between them when the patient interface is in use to provide respiratory support.

[0419] In another example a sampling port 538 or an outflow vent may be used as an access port if it is of sufficient size to receive the tube or tool. For example, a NG tube or gas sampling conduit may be inserted through a sampling port 538 as shown in Fig. 18, without the need for removal of the vent member 531. [0420] The outflow vents 530 shown in Fig. 8 and Fig. 9 are provided in body portion 521 however, as discussed above that need not be the case and at least one outflow vent may alternatively or additionally be provided in a gas delivery conduit (e.g. gas delivery side arm)

524 forming part of a patient interface system. The gas delivery side arm 524 may be formed integrally with or assembled together with the body portion 521 of the patient interface 520, and may be configured to provide a fluid connection at coupling 526 with an inspiratory conduit 110 (Fig. 1). Gas delivery side arm 524 may comprise a substantially rigid conduit configured to maintain patency and minimise crushing and/or kinking during provision of respiratory support however it is to be understood that such a gas delivery side arm may not be suitable for use in provision of respiratory support involving bag masking.

[0421] In some examples, gas delivery side arm 524 comprises a portion that may be less rigid compared to the rest of the conduit, such that a force acting on the collapsible portion may alter a parameter of the flow path through that portion. For example, a force acting on the collapsible portion may result in significantly reducing or stopping flow through the conduit and in some cases, by triggering reduction of flow from a flow source. Such a portion may be regarded as a collapsible portion 525 as illustrated in Fig. 10. The collapsible portion

525 may be a portion that closes or partially closes to reduce or stop flow through the sealing patient interface 520 e.g. when a pressure is applied to that portion. This may be useful or desirable in order to facilitate bag masking ventilation to the patient using a bag masking apparatus, applied over the patient interface 520. In some examples, excess flow can be vented out of the system 100 via a pressure relief valve (not shown) if required to maintain patient safety. In some examples, application of a force on the collapsible portion 525 can cause a pressure increase in the system 100 which can be detected by sensors that provide input to the control device 138 which in turn reduces the flow provided by the flow source 104.

[0422] In some configurations, bag masking the patient may be facilitated by a structure of the gas delivery conduit 524, which has collapsible portion 525 configured to transition from a first configuration in which a first level of gases is able to pass through the collapsible portion 525 to a second configuration in which a second level of gases is able to pass through the collapsible portion 525. [0423] In some configurations, the collapsible portion 525 is configured to be more collapsible or otherwise better adapted at changing the flow of gas through the collapsible portion 525 (therefore stopping or reducing the flow of gas through the conduit and to the patient) than other portions of the gas delivery conduit 524, and/or allowing a seal of a mask to seal over the top of the conduit. In other configurations the entire gas delivery conduit 524 may be configured to be collapsible.

[0424] In some embodiments, the first configuration is a substantially open configuration and the second configuration is a substantially closed configuration. That is, the gas delivery conduit 524 is configured to be more collapsible, deformable or otherwise adapted to fully or partially close off the flow at the collapsible portion 525 than at other portions of the gas delivery conduit 524. In the second configuration, the flow of gases to the nasal delivery elements may be reduced or stopped.

[0425] Fig. 11 shows one example of this configuration, in which the collapsible portion 525 of the gas delivery conduit 524 supplying the patient interface 520 of Fig. 10 is substantially closed by the seal 624 of face mask 620. In such an embodiment, the collapsible portion 525 (i.e. the more collapsible or deformable section) of the gas delivery conduit 524 should be of a length that is greater or equal to a width of a section of a seal 624 of the face mask 620 that bears over the collapsible portion of the gas delivery conduit. This may provide that the seal 624 of the face mask 620 does not bear over a non-collapsible section of the gas delivery conduit 524. For example, the collapsible portion 525 may extend from a distance of 35mm or less from a portion of the body portion 521 or the centre of a user's nose to at least 50mm from a portion of the body portion 521 or the centre of a user's nose. The collapsible portion 525 may have a length of at least about 5mm, about 1mm to about 30mm in length, or about 5mm to about 15mm in length, or about 10mm in length. In some embodiments the length of the first portion may be at least 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm or greater.

[0426] The collapsible portion 525 may progress between the first and second configurations based on a relative level of force applied to a wall of the collapsible portion 525. For example, as shown in Fig. 10, the force may be applied by the seal 624 of face mask 620. In this example, collapsible portion 525 is configured to be positioned under the seal 624 of the face mask 620. Alternatively, the force may be applied to collapsible portion 525 by other means, e.g., clamps (not shown), or alternatively a medical practitioner may compress the conduit by pressing on the conduit wall with a finger or thumb.

[0427] In some embodiments, the seal 624 of the face mask 620 acting on the collapsible portion 525 of the gas delivery conduit 524 causes the collapsible portion 525 to form a seal or at least an occlusion between the first patient interface 520 and the flow generator 122. Additionally, the seal of the face mask forms a seal or at least a partial seal over the collapsible portion 525 of the gas delivery conduit 524.

[0428] Bag masking may therefore be achieved simply by applying a second patient interface comprising a mask 620 such as a bag mask to the patient's face so that the seal of the mask collapses (partially or completely) the collapsible portion 525 of the gas delivery conduit 524 of the first patient interface 520. In some examples this stops or 'turns off' or reduces the respiratory support supplied by the patient interface 520 and also provides a substantial seal between the face mask 620 and the patient's face as well as the external surface of the collapsible portion 525 of the gas delivery conduit 524 such that respiratory support can be provided by the second patient interface comprising the mask 620 while the respiratory support provided by the first patient interface 520 is stopped or reduced.

[0429] The patient interface 520 with a collapsible portion 525 allows a user, such as an anaesthetist, nurse or clinician, to use a second patient interface such as a bag valve mask (i.e. bag mask) 620 to provide alternative respiratory support to the patient while also preventing or limiting provision of gases from the first patient interface 520 to the patient. The first patient interface 520 is structured and functions in a manner to reduce or close the delivery of high flow gases to the patient, and allow delivery of alternative respiratory support and/or respiratory therapy or anaesthesia gases through a mask when the collapsible portion 525 of the patient interface 520 is moved to a collapsed configuration. Relevantly, the at least one outflow vent 530 of the patient interface 520 can be sized to allow provision of a gases flow from the mask 620 to the patient and vice versa. The inserts 710 of Fig. 19 when applied to a patient nasal interface having a collapsible portion may also permit use of a mask 620 over the nasal interface since the at least one outflow vent 730 can be sized to allow provision of gases flow from the mask 620 to the patient and vice versa. It is to be understood that the inserts 710 need not be a separate component. In some examples, the inserts 710 may be integrated into the patient interface 520 e.g. incorporated into nasal prongs or cushions 522. Thus, the patient may be bag masked while the first patient interface remains on the patient's face in the collapsed configuration, notwithstanding the sealing elements (i.e. nasal pillows 522 or inserts 710) substantially sealing around the nasal prongs within the patient's nasal passages. In some embodiments removal of the mask 620 from the patient's face allows the respiratory support provided by the first patient interface 520 to resume, as the conduit returns from the collapsed configuration to the open configuration. Thus, the collapsible portion 524 may be resilient such that re-opens when the collapsing force is removed. Advantageously, the low RTF vents 530 in the first patient interface 520 (and vents 730 in the inserts 710) reduce the effect of flows exiting the sealing first patient interface on the bag masking process, and/or monitoring of a patient parameter (e.g. CO2) using sensors on the bag mask. This can also reduce any difference in "bag-feel" feedback experienced by the clinician during actuation of the bag when the bag mask 620 is applied over the first patient interface 520, when compared with the bag feel when applied directly to the patient's face. An advantage of this approach is that the first patient interface 520 (or nasal inserts 710) can remain in place if bag masking is required, which can critically save time e.g. in an emergency.

[0430] In some examples, patient interface 520 comprises a retention mechanism 540, such as a headgear connector which is best shown in the rotated view of Fig. 9. The headgear connector may comprise a fastener, clip or connector provided on one or both sides of the body portion 521 for connection of a headgear, such as head strap 542 (Figs 12 and 13) to secure the patient interface 520 in position once applied to the patient's face. The head strap may be removable from the connector 540, or it may be permanently fastened via the connector to the body portion 521.

[0431] In some examples, patient interface 520 may comprise a channel 550 through which a head strap 542 may pass, as shown in Figs 8, 9 and 12. The head strap 542 may freely pass through the channel 550, which may be located on the same side of the patient interface as the gas delivery conduit 524, and positioned such that when the head strap is passed through the channel and applied to the patient, the gas delivery conduit is substantially aligned with the head strap. This may reduce or avoid bending or kinking of the gas delivery conduit 524. Reduced movement of the gas delivery conduit 524 arising from passing the head strap 542 through the channel 550 may also reduce mechanical stress on the nasal pillows 522 forming a seal within the patient's nasal passages.

[0432] In another example shown in Fig. 13, one retention mechanism 540a may be provided on a non-gases delivery side of the body portion 521, and a second retention mechanism 540b may be provided on the gas delivery conduit 524 on an opposing side of the body portion but spaced from it. Location of the retention mechanism 540b on the gas delivery conduit 524 may apply tension on the gas delivery conduit when the head strap 542 is connected to the retention mechanisms 540a, b and applied to the patient, which may reduce or avoid bending or kinking of the gas delivery conduit 524.

[0433] In another example shown in Fig. 14, the patient interface 520 may comprise a non-gas delivery side arm 528 which comprises a retention mechanism 540 for connection of a headgear such as a head strap 542 to secure the patient interface 520 in position once applied to the patient's face. In such an arrangement, one retention mechanism 540a may be provided on the non-gas delivery side arm 528 spaced from the body portion 521 on one side, and a second retention mechanism 540b may be provided on the gas delivery side arm 524 spaced from the body portion on the other side. The patient interface 520 may or may not comprise a collapsible portion 525.

[0434] The body portion 521 comprises a chamber 532 defined between a gases inlet 534 to the patient interface 520, and the patient. The chamber 532 may comprise the entirety of the void inside the body portion 521 including inside the nasal pillows 522 through which the gases may flow. The chamber 532 is shown in the cross sectional views of Figs 15 and 16. In some examples, the chamber may be modified to cause asymmetrical pressures within the chamber 532 which in turn can create asymmetrical flow at the nares. This may have the beneficial effect of causing bulk flow through the nasal cavity and across the nasopharynx - at least at the end of expiration or at breath pauses (if the patient is spontaneously breathing) - or during apnoea. This can have a flushing effect in the upper airways and can improve airway dead space clearance. [0435] In one example shown in Fig. 15, asymmetrical flow arises due to the single gas delivery conduit 524 providing the flow of gases into the inlet 534. The entering gas stagnates asymmetrically in the chamber 532, creating a static pressure differential between the two nasal pillows 522 with a higher pressure generated in the part of the chamber distal to the inlet, near where the flow represented by the arrows turns. Increasing the velocity of the entering gas flow can increase the static pressure at the nasal pillow 522 located distally of the inlet 534.

[0436] In some examples, the chamber 532 comprises a restriction which disturbs the flow from the gases inlet 534 within the chamber 532. In some examples, a restriction may comprise a narrowing of the chamber 532 e.g. by shortening the distance between opposing wall portions represented between arrows N in Fig. 15. In another example a restriction 536 may comprise a perforated wall 536 as shown in Fig. 16. As the gases from the inlet 534 travel more distally within the chamber the restriction 536 restricts the flow increasing pressure on the proximal side relative to the distal side of the chamber causing asymmetrical flow. In other examples, the restriction may comprise e.g. a protrusion, porous web or other feature inside the chamber 532 generating asymmetrical flow to the patient's nares. One such feature may comprise the surface and/or shape of a portion of an internal wall of the chamber 532. For example, a portion of the wall may be angled, curved or comprise a surface texture that directs flows so that they enter the nares asymmetrically. In some examples involving a restriction for generating uneven flows in a chamber of the patient interface, at least one outflow vent should be provided on each side of the restriction for exit of flows from the chamber. In such an arrangement, the interface pressure, the pressure on each side within the chamber (i.e. on each side of the restriction) approximates the respective nare of the patient and the average of these pressures may represent the patient pressure within the nasal cavity.

[0437] The restriction may provide a physical feature separating the chamber 532 into two sides. The restriction may be used to achieve asymmetry between the two sides of the chamber 532. As a result, the patient's nasal passages will also experience pressure asymmetry when in use. This can be used to achieve bulk flow flushing of CO2 during nasal exhalation. The nature and/or size and/or degree of the restriction between the two sides of the chamber can determine the degree of asymmetry of the flow. Thus side entry of gases can be an enabling factor for asymmetry and improved CO2 flushing. Patient anatomy may also impact pressure asymmetry when in use, as can patient flows and flow rate provided to the patient interface (and then to the patient). In some examples, as the flow rate provided increases, for the same patient flow rate a greater degree of flushing may be observed.

[0438] Alternatively or additionally, the patient interface 520 may be configured such that there is jetting behaviour of gases into the chamber 532. In some examples, the jetting behaviour comprises directing incoming gas towards a side of the chamber 532 that is distal from the gases inlet 534. This may be achieved when high flows of gases (such as in NHF) are provided at the inlet 534 since the velocity of the flows enable the gas to penetrate further into the chamber 532 than would be the case for lower flow rate gases. This jetting behaviour can result in a flushing flow which can be achieved in use at the end of expiration that is independent of any restriction inside the chamber 532. It is to be understood that the asymmetry achieved by jetting behaviour of gases entering the chamber 532 may be provided as an alternative, or in addition, to a restriction in the chamber 532 which also provides asymmetry.

[0439] In some examples, it may be desirable to determine one or more characteristics of gas inside the chamber 532 therefore at least one sampling port may be provided. An example of a patient interface 520 comprising sampling ports 538 is provided in Fig. 18. Although Fig 18 shows two sampling ports, in some examples there may be more sampling ports. In other examples, only one sampling port may be provided. The at least one sampling port may be couplable with or provide a sampling line that provides fluid communication between the sampling port and a sensor or measurement device. The sensor or measurement device may be provided in a control device 138 of the system or may comprise a separate component that is in operative communication with the control device. Operative communication may involve wired and/or wireless communication of sensor signals from the sensor or measurement device to the control device. 138. Thus, the at least one sampling port provides access for fluid communication between the gas inside the chamber 532 and a sensor such as a pressure sensor, gas species or gas composition sensor (e.g. capnograph or gas analyser), temperature or humidity sensor. Gas species of interest may include CO2, 02 and N2, for example. In one example shown in Figure 18, a sampling port 538 may be provided for measurement of patient interface pressure and a sampling port may be provided for measurement of gas (e.g. CO2) composition. In another example (not shown) a single sampling port 538 is provided for measurement of patient interface pressure.

[0440] In some cases, such as when the patient is expiring through the mouth rather than through the nose, it may be desirable to enable sampling of gas from the oral region in order to determine e.g. gas composition. Therefore, in some examples the patient interface may include an adjustable gas sampling conduit having a sampling tip that is positioned or positionable proximate to the oral region in order to sample expired gases from the mouth. The gas sampling conduit may be adjustable by use of a manipulatable core such as a malleable wire that permits the location of the sampling tip to be adjusted prior to or during use of the patient interface. In some examples, the gas sampling conduit may be removably attachable to the patient interface 520. Attachment may be via a clip, magnet, friction fit or the like that attaches the gas sampling conduit to the patient interface at a location that is sufficiently rigid to support the gas sampling conduit. Suitable locations for attachment of the gas sampling conduit may comprise e.g. the coupling 526 and the vent member 531. The gas sampling conduit may be couplable with or provide a sampling line that provides fluid communication between the sampling tip and a sensor or measurement device. Use of the gas sampling conduit in conjunction with a sampling port 538 permit both nasal and mouth sampling at the same time. Sampling through the at least one sampling port 538 and/or the gas sampling conduit enables measurement of gas characteristics, including pressure, gas composition, temperature, humidity or the like to be periodic or substantially continuous. In another example, the patient interface may not have any sampling ports 538 and the gas sampling conduit may be manipulatable and selectively positionable such that the gas sampling conduit can be moved to sample from either the oral region, or from a region near or adjacent the at least one outflow vent of the patient interface. That is, the gas sampling port could be moved to a position near (e.g. in front of) at least one outflow vent where it can sample expired gases which exit the chamber of the patient interface via the at least one outflow vent. In examples where the patient interface has sampling ports 538, the gas sampling conduit may also be positionable to sample from outside of at least one outflow vent in this manner.

[0441] Determining the pressure inside the patient interface 520 may be desirable for several reasons. For example, interface pressure may be used as a proxy for patient nasal cavity pressure. Furthermore, patient interface pressure may be used to provide an indication that the interface is well sealed on the patient's face, and if there are significant leaks. Interface pressure may be measured directly by using a pressure sensor connected to a sampling port 538 as described above. Alternatively or additionally, interface pressure may be determined or estimated indirectly, from other pressure measurements within the system 100. Directly or indirectly obtained interface pressure values can be used by a control device 138 to control elements of system 100 and/or for presentation on a user interface 140.

[0442] Interface pressure may be determined indirectly, using a pressure measurement upstream from the sealed patient interface, and applying knowledge of pressure drop of other components within the system 100. The pressure measured at the start of the high flow system 100 (i.e. the flow source 104) is a summation of the pressure drops within each component (humidifier 108, conduit 110, 114, etc.) in the system. Each component of the system can be characterized so that the pressure drop through each component is known for a particular supply flow rate when assembled as the system. This characterisation can be predetermined in a benchtop test. Characterization of the pressure drop through each component enables an estimation of the interface pressure as the interface pressure is the measured system pressure less the summation of pressure drops across components between the location of measured system pressure in the system 100 and the interface 520. The interface pressure may be specifically the pressure within chamber 532 and thus, one of the components for which the pressure drop may be characterised could be any interface conduits upstream of the chamber 532 (even if they are integrally formed with the chamber). Using this technique, pressure can be estimated anywhere in the system 100 upstream of the chamber 532 and pressure within the patient interface 520 (and specifically, the chamber 532) can be estimated without the need for direct measurement of pressure within the patient interface/chamber. This may be beneficial as it does not require provision of a sensor or a coupling to a sensor in the interface itself thus avoiding components near the patient's face that can be obtrusive. However, indirect measurements can be less accurate if there is e.g. unintentional bending or kinking of a supply conduit as this can impact the resistance to flow through components in the system. For this reason, it may be preferred to provide direct pressure measurements via a sampling port 538 when accuracy of patient interface pressure values is important. [0443] As discussed above, aspects of the present disclosure facilitate bag masking the patient over a substantially sealing nasal interface as disclosed herein. Fig. 17 is a flow chart showing schematically, steps in such a method 700 of providing respiratory support which involves bag masking. In a step 702, a first patient interface is used to provide a first respiratory support to the patient. The first respiratory support may be provided during a pre-oxygenation stage of a medical procedure, prior to administration of anaesthesia to the patient. The method may comprise a prior step 701 of applying the first patient interface 520 to the patient. In some examples, the method of providing respiratory support, may comprise in a step 703, administration of anaesthesia. In a step 704, a second patient interface such as a bag mask, is applied over the first patient interface reducing or stopping flow of the first respiratory support to the first patient interface. The second patient interface may comprise a vent or expiratory path for exhausting gases. In a step 706, a second respiratory support is provided to the patient using the second patient interface. The second respiratory support may comprise "bag masking"; a technique providing flows to the patient by manual actuation of the bag, and is typically administered in emergency situations, or prior to intubation of the patient. As disclosed in the foregoing, the first patient interface comprises at least one vent (also referred to herein as outflow vent) sized such that the second respiratory support from the second patient interface can be provided to the patient via the first patient interface including when the patient's mouth is closed.

[0444] The first patient interface may comprise features as disclosed elsewhere herein. A collapsible portion in the gas delivery conduit (as described with reference to Figs 10 and 11) substantially closes upon application of a force arising when the mask seal of the second patient interface is applied over the first patient interface, thereby significantly reducing or stopping flows to the first patient interface. The at least one vent provides a low RTF thereby providing a flow path from the second patient interface into the chamber of the first patient interface where it travels into the nares via nasal pillows, prongs or inserts of the first patient interface. Unlike bag masking over a conventional non-sealing Nasal HF patient interface, the first patient interface according to the present disclosure comprises at least one sealing element forming a substantial seal with the patient's nare. In contradistinction to conventional HF systems where gas flows to the nasal airways from the bag mask around the nasal prongs, in the present method the gas flows to the nasal airways from the bag mask though the first patient interface and through the sealing nasal pillows, into the nares. The method may comprise in step 708 removing the second patient interface to resume providing the first respiratory support. The method may further comprise the step of alternating between the first respiratory support and the second respiratory support by removal or application of the second patient interface according to the steps in method 700.

[0445] In some examples, the first respiratory support provided in step 702 is described elsewhere herein and comprises controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one vent at a first exhaust flow rate; and controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a second rate of change in the second interface pressure associated the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate. Such methods have been described in relation to Fig. 2 and Fig. 3.

[0446] The at least one vent may be configured to provide a first predetermined resistance to flow in use in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l for a first exhaust flow value that is in a rate range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM; or when the supply flow rate is below 15 LPM. The at least one vent may be configured to provide a second predetermined resistance to flow in use in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

[0447] In some examples, patient interface may comprise at least one outflow vent having a RTF which is very low, such that the at least one outflow vent is highly permissive of flows in both directions in and out of the interface. In such examples, the total RTF of the at least one outflow vent may be between greater than about 0 cmH20/Lmin-l to about 0.5 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH20/Lmin-l, or between greater than about 0 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.05 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.1 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l, or between greater than about 0.15 cmH20/Lmin-l to less than about 0.5 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.4 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.3 cmH20/Lmin-l . Supply flow rates may be greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, or about 50 LPM, or higher such as about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM, about 100, about 110 LPM, about 120 LPM, about 130 LPM, about 140 LPM, or about 150 LPM or a value in between. The supply flow rate may be about or the same as the exhaust flow rate, or higher.

[0448] As described elsewhere herein, the first respiratory support may comprise providing a flow of gases at a supply flow rate to the patient interface and generating an interface pressure and an exhaust flow through the at least one vent at an exhaust flow rate, wherein values of interface pressure and values of exhaust flow rate comprise a non-linear relationship. The non-linear relationship may comprise a polynomial component, preferably of degree two.

[0449] The second respiratory support may be provided to achieve one or more effects in the patient such as, but not limited to: increase in patient oxygenation, delivery of one or more substances to the patient's airway, change in interface pressure e.g. to increase pressure in the patient's upper and/or lower airways to clear an obstruction such as a soft palate closure or to check airway patency, change in gases flow rate, different control over interface pressure than what can be achieved using the first respiratory support, and different control over gases flow rate.

[0450] Aspects of the present disclosure provide methods, systems and devices for provision of respiratory support that allow for generation of a patient pressure and an exhaust flow rate at high supply flow rates that provide advantages over conventional nonsealing HF respiratory support. One advantage is the higher interface pressure generated (e.g. up to about 15 cmH20) with higher exhaust flow rates. When used in a flow controlled system as disclosed herein, the methods and systems using the sealing patient interface of the present disclosure can generate high interface pressures, particularly during patient exhalation and this can translate to higher patient airway pressure, particularly in the nasal airway. Sealing patient interfaces have been used in anaesthetic procedures however due to their restrictive bias flow vents which are required for pressure-based respiratory support, these interfaces are not suitable for use in high flow systems as their use could present risks to the patient, such as risk of barotrauma and/or gastric insufflation.

[0451] Unlike CPAP, the presently disclosed methods, systems and devices which are flow controlled and permit provision of high supply flow rates and exhaust flow rates may provide for good airway clearance that may reduce rebreathing of gas high in CO2 and depleted 02, thereby improving oxygenation. Airway clearance may be improved due to rapid flushing of the patient interface dead space with fresh supplied gas, since the flow throughput (i.e. amount of fresh gas supplied to the patient interface in a given time, is equal to the amount of gas exhausted from the patient interface in a given time (ignoring patient breathing)) is likely higher than a CPAP interface. Alternatively or additionally, asymmetric nostril gas pressure may create a nasal cavity flushing flow, for example during and near breath pauses.

[0452] Aspects of the present disclosure provide methods, systems and devices providing high flow respiratory support that controls a flow rate of a gas flow provided to the patient and generates an exhaust flow with an exhaust flow rate from the at least one outflow vent of the patient interface and an interface pressure. The exhaust flow rate (Q) and interface pressure (P) may be related, through configuration of the at least one outflow vents to provide a predefined RTF for a range of supply flow rates (e.g. in a simulation or test environment), with a PQ profile such that as exhaust flow rates increase, the rate of change in patient pressure increases. This can provide clinicians with a useful choice to obtain a substantially higher patient pressure at higher flow rates compared to conventional nonsealing NHF. This could be used by clinicians to achieve a more desirable pressure-based clinical effect but in a flow controlled, high flow system. This may be especially beneficial in at-risk groups (e.g. high BMI), by improving upper airway patency, reducing atelectasis and improving overall oxygenation etc, during anaesthetic procedures. [0453] As noted above, permitting high flow exhaust flow rates through the patient interface also provides for good bag-mask compatibility during anaesthetic procedures. The ability to bag-mask a patient over the nasal patient interface is made easier since flows generated from the actuation of the bag can easily flow from the mask to the patient and vice versa through at least one low RTF outflow vents in the nasal patient interface. Advantageously, this also reduces difference in 'bag-feel' i.e. feedback a clinician receives during actuation of the bag, and actual patient pressure, especially if the mouth is closed. In contrast, delivering bag-masking over a nasal interface having bias flow vents with a higher RTF may require a clinician to actuate the bag to a greater extent to achieve a certain patient pressure or tidal volume, compared to one or more vents with a low RTF. Actuating the bag to a greater extent can result in an abnormal bag feel compared to bag actuation without an underling patient interface with higher RTF. This could make delivering breaths from the bag more difficult for a clinician and may impact patient therapy.

[0454] Aspects of the present disclosure can reduce variability of the gases exhaust flow path from the patient by provision of a patient interface having at least one outflow vent and a sealing element, where the sealing element can substantially limit escape of gases from the patient except via the at least one outflow vent. This in turn reduces the variability of interface pressure (which may be a proxy for pressure generated in the nasal cavity) at a given supply/exhaust flow rate. This contrasts with conventional NHF with a non-sealing nasal cannula where there is uncontrollable leak due to the inter-patient variability in the exhaust flow path between the nasal prong and the patient's nares, causing wider interpatient variability in interface pressure, particularly at higher exhaust flow rates.

[0455] A PQ profile with minimal or no variability in patient pressure at a given exhaust flow rate (e.g. in the absence of breathing or as determined in a simulation) provides improved performance consistency and patient pressure expectations for clinicians when controlling to various flow rates.

[0456] In this specification, it is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0457] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components or group thereof.

[0458] It is to be understood that various modifications, additions and/or alterations may be made to the parts previously described without departing from the ambit of the present invention as defined in the claims appended hereto.

[0459] Future patent applications may be filed on the basis of or claiming priority from the present application. It is to be understood that the following claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the claims at a later date so as to further define or re-define the invention or inventions.

Alternative aspects are set out in the following first and second sets of clauses:

First clauses

1. A patient interface for provision of respiratory support, the interface comprising:

- a gases flow path for provision of a gases flow to the patient;

- at least one outflow vent configured to permit an exhaust flow of gases; and

- a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use; wherein the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape.

2. The patient interface according to clause 1, wherein the at least one outflow vent comprises at least one small opening and at least one large opening.

3. The patient interface according to clause 2, wherein the at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm.

4. The patient interface according to clause 2 or clause 3, wherein the at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about 1 mm to about 2 mm or about 2 mm to about 3mm.

5. The patient interface according to any one of clauses 2 to 4, wherein a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

6. The patient interface according to any one of clauses 2 to 5, wherein when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening.

7. The patient interface according to any one of clauses 2 to 6, wherein when in use, flows from the at least one small opening are directed towards the patient's mouth.

8. The patient interface according to any one of clauses 2 to 7, wherein when in use, flows from the at least one large opening are directed away from the patient's mouth. The patient interface according to any one of clauses 1 to 8, wherein the patient interface is configured to generate an interface pressure during provision of the respiratory support.

Second clauses

1. A patient interface for provision of respiratory support, the patient interface comprising:

- a gases flow path for provision of a gases flow to the patient;

- at least one outflow vent configured to permit an exhaust flow of gases at an exhaust flow rate; and

- a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use; wherein the at least one outflow vent has a predetermined resistance to flow in use.

2. The patient interface according to clause 1, wherein the predetermined resistance to flow of the at least one outflow vent is in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l when the exhaust flow rate is between more than about 0 LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM.

3. The patient interface according to clause 1 or 2, wherein the predetermined resistance to flow of the at least one outflow vent is in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l when the exhaust flow rate is between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM.

4. The patient interface of any one of clauses 1 to 3, wherein the predetermined resistance to flow is measurable in a simulation test.

5. The patient interface according to any one of clauses 1 to 4, wherein, in use, a supply flow rate is provided to the patient interface to generate an interface pressure and the exhaust flow through the at least one outflow vent at the exhaust flow rate. 6. The patient interface according to any one of clauses 1 to 5, wherein a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm2, or about 35 mm2 to about 80 mm2 or about 35 mm2 to about 60 mm2, or about 35 mm2 to about 50 mm2, or about 35 mm2 to about 40 mm2, or about 35 mm2 to about 45 mm2.

7. The patient interface according to any one of clauses 1 to 6, wherein the patient interface comprises at least one gas delivery element configured to provide the gases flow into the nares of the patient, and the at least one outflow vent comprises:

- at least one opening in at least one insert locatable in the nare around the at least one gas delivery element.

8. The patient interface according to clause 7, wherein the sealing element is provided by the at least one insert.

9. The patient interface according to clause 7 or clause 8, wherein the at least one insert is provided separately from the patient interface.

10. The patient interface according to any one of clauses 1 to 6, wherein the patient interface comprises at least one gas delivery element configured to provide the gases flow into one or both of the patient's nares.

11. The patient interface according to any one of clauses 1 to 6 and 10, wherein the sealing element comprises at least one nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare.

12. The patient interface according to any one of clauses 10 to 11, wherein the sealing element is integrated with or into the gas delivery element and optionally, wherein the sealing element comprises the at least one outflow vent.

13. The patient interface according to any one of clauses 1 to 12, wherein the patient interface comprises a body portion comprising the at least one outflow vent. 14. The patient interface according to clause 13, wherein the body portion comprises a chamber between a gases inlet to the patient interface and the patient, the chamber comprising a restriction causing asymmetrical flow to the patient's nares.

15. The patient interface according to any one of clauses 1 to 14, wherein the patient interface comprises a gases delivery side member comprising a collapsible portion that closes or partially closes to reduce or stop flow through the first patient interface.

16. The patient interface according to clause 15 wherein the collapsible portion is configured to collapse upon application of a force arising from placement of a respiratory mask over the patient interface.

17. The patient interface according to any one of clauses 1 to 16 wherein the at least one outflow vent is sized to allow provision of a gases flow from the respiratory mask to the patient.

18. The patient interface according to clause 16 or clause 17, wherein the respiratory mask comprises a bag valve mask.

19. The patient interface according to any one of clauses 1 to 18, wherein the patient interface is configured to generate an asymmetrical flow profile into the patient's nares.

20. The patient interface according to any one of clauses 1 to 19, wherein the patient interface is configured to receive side entry of gases, preferably single side entry.

21. The patient interface according to any one of clauses 1 to 20 comprising at least one sampling port.

22. The patient interface according to clause 21, wherein the at least one sampling port is couplable with or provides a gas sampling line to provide fluid communication of gases in the patient interface to at least one sensor, optionally wherein the at least one sensor comprises a pressure, temperature, gas composition, CO2 or humidity sensor.

23. The patient interface according to any one of clauses 1 to 22 comprising at least one gas sampling conduit that is adjustable to locate a sampling tip at an oral region of the patient when in use. 24. The patient interface according to clause 23, wherein the gas sampling conduit is attachable such as removably attachable, to the patient interface.

25. The patient interface according to any one of clauses 1 to 24, comprising at least one access port that is normally closed and is openable to provide instrument access to the nasal cavity via the patient interface.

26. The patient interface according to clause 25, wherein the access port comprises a removable cover and optionally, wherein the removable cover comprises one or more of the at least one outflow vent.

27. The patient interface according to any one of clauses 1 to 26, wherein the patient interface comprises a headgear connector to stabilise the patient interface on the patient when in use.

28. The patient interface according to any one of clauses 1 to 27, wherein the patient interface comprises a retention mechanism configured to improve sealing by the sealing element.

29. The patient interface according to any one of clauses 1 to 29, wherein the at least one outflow vent is configured to generate in use, a pressure differential between the patient and atmosphere comprising about 7cmH2O to about 15cmH2O at a supply flow rate of about 70 L/min.

30. The patient interface according to any one of clauses 1 to 30, wherein the at least one outflow vent is configured to generate exhaust rates from the patient interface substantially corresponding to a supplied flow rate of gas while the patient's mouth is closed and during breath hold or while the patient is apnoeic.

31. The patient interface according to any one of clauses 1 to 30, wherein the at least one outflow vent comprises a size and/or shape that is non-variable.

32. The patient interface according to any one of clauses 1 to 31, wherein the at least one outflow vent comprises a cross sectional shape comprising a circle, ellipse, oval, obround, quadrilateral, or squircle. The patient interface according to any one of clauses 1 to 32, wherein the at least one outflow vent comprises 1 or 2 or 3 or 4 or 5 or 6 discrete openings. The patient interface according to any one of clauses 1 to 33, wherein the at least one outflow vent comprises 6 discrete openings each having a cross sectional dimension of about 3 mm. The patient interface according to any one of clauses 1 to 34, wherein the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape. The patient interface according to any one of clauses 1 to 34, wherein the at least one outflow vent comprises at least one small opening and at least one large opening. The patient interface according to clause 36, wherein the at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm. The patient interface according to clause 36 or clause 37, wherein the at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about 1 mm to about 2 mm or about 2 mm to about 3mm. The patient interface according to any one of clauses 36 to 38, wherein a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening. The patient interface according to any one of clauses 36 to 39, wherein when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening. The patient interface according to any one of clauses 36 to 40, wherein when in use, flows from the at least one small opening are directed towards the patient's mouth. The patient interface according to any one of clauses 36 to 41, wherein when in use, flows from the at least one large opening are directed away from the patient's mouth. The patient interface according to any one of clauses 1 to 42, wherein the at least one outflow vent is shaped to generate transitional or turbulent flow characteristics, preferably at flow rates above about 50 LPM. The patient interface according to any one of clauses 1 to 43, comprising a vent member comprising the at least one outflow vent. The patient interface according to clause 44, wherein the vent member is removable to provide instrument access to the nasal cavity via the patient interface. A system for providing respiratory support to a patient, the system comprising:

- a patient interface for providing a gases flow to the patient, the patient interface having at least one outflow vent to permit an exhaust flow of gases at an exhaust flow rate, and a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use;

- a gases source operable to provide a gases flow; and

- a controller operable to control a flow rate of a gases flow provided to the patient interface at a predetermined supply flow rate; wherein the at least one outflow vent has a pre-determined resistance to flow in use. The system according to clause 46, comprising a flow source controllable by the controller to provide the gases flow at the predetermined supply flow rate. The system according to clause 46 or clause 47, comprising the patient interface according to any one of clauses 1 to 45. The system according to any one of clauses 46 to 48, comprising a humidifier. The system according to any one of clauses 46 to 49, wherein the predetermined supply flow rate is in a range of greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM 51. The system according to any one of clauses 46 to 50, wherein the controller is operable to control the predetermined supply flow rate at a first supply flow rate that is greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM or about 50 LPM.

52. The system according to clause 51, wherein the controller is operable to control the predetermined supply flow rate at a second supply flow rate that is higher than the first supply flow rate and optionally, that is greater than about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM.

53. The system according to clause 52, wherein the second supply flow rate is provided in response to an indication of a patient condition.

54. The system according to clause 53, wherein the indication of the patient condition is determined by one or more of:

- observation of the patient and/or patient parameters;

- user confirmation of administration of therapy to the patient;

- instrumented measurement of one or more patient parameters;

- the patient self-describing their condition.

55. The system according to clause 54, wherein the one or more patient parameters comprise:

- depth of sedation;

- heart rate;

- EEG signal values;

- EKG/ECG signal values;

- blood oxygen concentration;

- blood oxygen saturation (SpO2);

- expired oxygen concentration;

- blood CO2 concentration;

- transcutaneous CO2 concentration (TcCO2);

- transcutaneous 02 concentration (TcO2); - expired CO2 concentration; and

- blood glucose level.

56. The system according to any one of clauses 53 to 55, wherein the patient condition comprises a condition selected from a group comprising:

- lower or upper airway obstruction;

- soft palate obstruction;

- absence of spontaneous breathing;

- patient inspiratory demand not being met;

- the patient is or is at risk of becoming apnoeic;

- patient depth of sedation being met; and

- expiratory airway pressure is, or is approaching, a non-optimal threshold.

57. The system according to any one of clauses 53 to 56, wherein the controller is operable to control the first and/or second supply flow rate by one or more of: manual selection by a user of the second supply flow rate in response to the user confirming the indication of the patient condition; a control device determining the second supply flow rate when the control device receives a user input confirming the indication of the patient condition; and a control device determining the second supply flow rate when the control device determines the existence of the patient condition using data received from one or more devices monitoring patient condition parameters.

58. The system according to any one of clauses 46 to 57, operable to provide a first supply flow rate before delivery of an anaesthetic agent to the patient, and providing a second supply flow rate after delivery of an anaesthetic agent to the patient.

59. The system according to any one of clauses 53 to 58, operable to provide the second supply flow rate in response to an indication that an anaesthetic agent is being or has been delivered to the patient.

60. The system according to clause 59, wherein the indication that an anaesthetic agent is being or has been delivered to the patient is determined by one or more of: clinician observation of the patient and/or patient parameters and manual entry of the indication to a control device; and a control device using data received from a user or one or more Ill devices monitoring patient parameters that provide an indication of an anaesthetic agent being or having been delivered to the patient. The system according to any one of clauses 46 to 60, operable to provide the respiratory support prior to anaesthetic agent delivery and/or prior to onset of anaesthesia or sedation in the patient. The system according to any one of clauses 53 to 60, operable to control the gases flow at a third supply flow rate. The system according to clause 62, wherein the third supply flow rate is less than the second supply flow rate. The system according to clause 62 or clause 63, operable to provide the third supply flow rate in response to an indication of a different patient condition. The system according to clause 64, wherein the different patient condition comprises a condition selected from a group comprising: lower or upper airway becoming patent; soft palate no longer obstructing; presence of spontaneous breathing; patient inspiratory demand being met; predetermined level of alertness being met; and expiratory interface pressure meets or exceeds an optimal threshold. The system according to any one of clauses 46 to 65, wherein the controller is configured to receive user supplied control inputs and/or processor generated control inputs. The system according to any one of clauses 46 to 66, wherein the patient interface is configured to provide the gases flow into one or both of the patient's nares. The system according to any one of clauses 46 to 67, operable to provide respiratory support to a patient undergoing a medical procedure, such as a scheduled medical procedure. The system according to any one of clauses 46 to 68, wherein the gases flow provided at the predetermined supply flow rate comprises 100% 02 concentration. 70. The system according to any one of clauses 46 to 69, wherein a first predetermined resistance to flow of the at least one outflow vent at a first exhaust flow rate through the at least one outflow vent is in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l.

71. The system according to any one of clauses 70, wherein the first exhaust flow rate is between more than about 0 LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM.

72. The system according to any one of clauses 46 to 71, wherein a second predetermined resistance to flow of the at least one outflow vent at a second exhaust flow rate is in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.4 cmH2O/Lmin-l, or about 0.2 cmH2O/Lmin-l to about 0.3 cmH2O/Lmin-l.

73. The system according to clause 72, wherein the second exhaust flow rate is between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM.

74. The system according to any one of clauses 46 to 73, wherein for a given exhaust flow rate, the resistance to flow is attributable to a size and/or shape of the at least one outflow vent.

75. The system to any one of clauses 46 to 74, wherein a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm2, or about 35 mm2 to about 80 mm2 or about 35 mm2 to about 60 mm2, or about 35 mm2 to about 50 mm2, or about 35 mm2 to about 40 mm2, or about 35 mm2 to about 45 mm2.

76. The system according to any one of clauses 46 to 77, operable to control the gases flow and generating one or more of:

- an exhaust flow rate of about 30 LPM an interface pressure of about 2-4 cmH20, such as about 3 cmH20;

- an exhaust flow rate of about 55 LPM and an interface pressure of about 6-8 cmH20; - an exhaust flow rate of about 60 LPM and an interface pressure of about 7-9 cmH20; and

-an exhaust flow rate of about 70 LPM and an interface pressure of about 7-15 cmH20, such as about 9-12 cmH20, such as about 9-10 cm H2O or about 10-12 cmH20.

Claims

1. A method of providing respiratory support to a patient during a medical procedure, the method comprising:

- providing a gases flow to the patient via a patient interface system having at least one outflow vent;

- controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; and

- controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow through the at least one outflow vent at a second exhaust flow rate; wherein a first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is different than a second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

2. A method of providing respiratory support to a patient during a medical procedure, the method comprising:

- controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate;

- controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate;

- wherein a second rate of change in the second interface pressure associated with the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate.

3. The method according to claim 1 or claim 2, comprising controlling the gases flow at the first supply flow rate before the second supply flow rate.

4. The method according to claim 1 or claim 2, comprising controlling the gases flow at the second supply flow rate before the first supply flow rate.

5. The method according to any one of the preceding claims, wherein the second supply flow rate is higher than the first supply flow rate.

6. The method according to any one of the preceding claims, wherein the first supply flow rate is greater than about 0 LPM, about 10 LPM, about 20 LPM, about 30 LPM, about 40 LPM, or about 50 LPM.

7. The method according to any one of the preceding claims, wherein the second supply flow rate is greater than about 40 LPM, about 50 LPM, about 60 LPM, about 70 LPM, about 80 LPM, about 90 LPM or about 100 LPM.

8. The method according to any one of the preceding claims, comprising providing the second supply flow rate in response to an indication of a patient condition.

9. The method according to claim 8, wherein the indication of the patient condition is determined by one or more of:

- observation of the patient and/or patient parameters;

- user confirmation of administration of therapy to the patient;

- measurement of one or more patient parameters;

- the patient self-describing their condition.

10. The method according to claim 9, wherein the one or more patient parameters comprise:

- depth of sedation;

- heart rate;

- EEG signal values;

- EKG/ECG signal values;

- EMG signal values;

- blood oxygen concentration;

- blood oxygen saturation (SpO2);

- expired oxygen concentration;

- blood CO2 concentration; - transcutaneous CO2 concentration (TcCO2);

- transcutaneous 02 concentration (TcO2);

- expired C02 concentration; and

- blood glucose level.

11. The method according to any one of claims 8 to 10, wherein the patient condition comprises a condition selected from a group comprising:

- lower or upper airway obstruction;

- soft palate obstruction;

- absence of spontaneous breathing;

- patient inspiratory demand not being met;

- the patient is or is at risk of becoming apnoeic;

- patient depth of sedation being met; and

- expiratory airway pressure is, or is approaching, a non-optimal threshold.

12. The method according to any one of claims 8 to 11, comprising controlling the first and/or second supply flow rate by one or more of:

- manual selection by a user of the second supply flow rate in response to the user confirming the indication of the patient condition;

13. The method according to any one of the preceding claims, comprising providing the first supply flow rate before delivery of an anaesthetic agent to the patient, and providing the second supply flow rate after delivery of an anaesthetic agent to the patient.

14. The method according to any one of the preceding claims, comprising providing the second supply flow rate in response to an indication that an anaesthetic agent is being or has been delivered to the patient.

15. The method according to claim 14, wherein the indication that an anaesthetic agent is being or has been delivered to the patient is determined by one or more of:

16. The method according to any one of the preceding claims, comprising providing the respiratory support prior to anaesthetic agent delivery and/or prior to onset of anaesthesia or sedation in the patient.

17. The method according to any one of the preceding claims, comprising controlling the gases flow at a third supply flow rate and generating a third interface pressure and an exhaust flow through the at least one outflow vent at a third exhaust flow rate, wherein a rate of change in the third interface pressure associated with a change in the third exhaust flow rate is less than a rate of change in the second interface pressure associated with a change in the second exhaust flow rate.

18. The method according to any one of the preceding claims, comprising controlling the gases flow at a third supply flow rate and generating a third interface pressure and an exhaust flow rate through the at least one outflow vent at a third exhaust flow rate, wherein a third predetermined resistance to flow of the at least one outflow vent at the third exhaust flow rate is different than the second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

19. The method according to claim 17 or claim 18, wherein the third supply flow rate is lower than the second supply flow rate.

20. The method according to any one of claims 17 to 19, comprising providing the third supply flow rate in response to an indication of a different patient condition.

21. The method according to claim 20, wherein the different patient condition comprises a condition selected from a group comprising:

- lower or upper airway becoming patent; - soft palate no longer obstructing;

- presence of spontaneous breathing;

- patient inspiratory demand being met;

- predetermined level of alertness being met; and

- expiratory interface pressure meets or exceeds an optimal threshold.

22. The method according to any one of claims 2 to 21, wherein the first rate of change in the first interface pressure may be in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.05 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.1 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l for a first exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM.

23. The method according to any one of claims 2 to 22, wherein the second rate of change in the second interface pressure may be in a range of greater than about 0.1 cmH20/Lmin-l to less than about 0.6 cmH20/Lmin-l, or about 0.15 cmH20/Lmin-l to about 0.5 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.4 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.3 cmH20/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

24. The method according to any one of claims 2 to 23, wherein the respective interface pressure and exhaust flow rate of the first rate of change and the second rate of change are related such that when presented graphically, their relationship comprises one or more of:

- a non-step change at a transition between the first exhaust flow rate and the second exhaust flow rate; - a non-step change at a transition between the second exhaust flow rate and a third exhaust flow rate.

25. The method according to any one of claims 2 to 24, wherein one or both of the first rate of change and the second rate of change is non-constant.

26. The method according to any one of the preceding claims, comprising controlling the gases flow and generating one or more of:

27. The method according to any one of the preceding claims, comprising operating a flow source to provide the gases flow, wherein the flow source is controlled by a control device configured to receive user supplied control inputs and/or processor generated control inputs.

28. The method according to any one of the preceding claims, wherein the patient interface system comprises a patient interface configured to provide the gases flow into one or both of the patient's nares, and comprising at least one outflow vent configured to generate a predetermined interface pressure and a predetermined target exhaust flow rate out of the at least one outflow vent for a predetermined supply flow rate to the patient interface.

29. The method according to any one of the preceding claims, wherein the patient interface comprises at least one sealing element, such as a nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare to substantially limit escape of gases except via the at least one outflow vent.

30. The method according to claim 28 or claim 29, comprising the step of placing the patient interface on the patient.

31. The method according to any one of the preceding claims, wherein the patient is undergoing a medical procedure during provision of the respiratory support, such as a scheduled medical procedure.

32. The method according to any one of the preceding claims, comprising providing anaesthetic agent to the patient.

33. The method according to any one of the preceding claims, wherein the gases flow provided at one or both of the first supply flow rate and the second supply flow rate comprises 100% 02 concentration.

34. The method according to any one of claims 2 to 34, wherein the rate of change is an average rate of change.

35. The method according to claim 1 or any one of claims 3 to 34 when appended to claim 1, wherein the first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is in a range of greater than about 0 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l.

36. The method according to any one of the preceding claims, wherein the first exhaust flow rate is between more than about 0 LPM to about 40 LPM, or between about 30 LPM to about 40 LPM or between about 35 to about 45 LPM.

37. The method according to claim 1 or any one of claims 3 to 36 when appended to claim 1, wherein the second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate is in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.4 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.3 cmH20/Lmin-l.

38. The method according to any one of the preceding claims, wherein the second exhaust flow rate is between more than about 40 LPM to about 100 LPM, or between about 40 LPM to about 70 LPM, or between about 40 LPM to about 60 LPM, or between about 50 LPM to about 70 LPM, or between about 50 PM to about 60 LPM, or between about 60 LPM to about 70 LPM.

39. The method according to any one of the preceding claims, wherein the first and second resistance to flow at the respective exhaust flow rates, and/or the first and second rate of change, are measurable in a simulation test.

40. The method according to any one of the preceding claims, wherein the patient is not apnoeic during the provision of the respiratory support.

41. The method according to claim 1 and any one of claims 3 to 40 when appended to claim 1, wherein for a given exhaust flow rate, the resistance to flow is attributable to the size and/or shape of the at least one outflow vent.

42. The method according to any one of the preceding claims, wherein a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

43. A patient interface for provision of respiratory support, the interface comprising:

- a gases flow path for provision of a gases flow to the patient;

- at least one outflow vent configured to permit an exhaust flow of gases; and

- a sealing element substantially preventing escape of gas from the patient except via the at least one outflow vent when in use; wherein the patient interface is configured to generate an interface pressure during provision of the respiratory support; and wherein the interface pressure and the exhaust flow rate through the at least one outflow vent comprise a non-linear relationship comprising a rate of change of the interface pressure in a range of more than 0.15 cmH20/Lmin-l to less than 0.5 cmH20/Lmin-l for an exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

44. The patient interface according to claim 43, wherein the non-linear relationship comprises a rate of change of the interface pressure in a range of greater than about 0 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.05 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l, or about 0.1 cmH20/Lmin-l to about 0.15 cmH20/Lmin-l for an exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM.

45. The patient interface of claim 43 or 44, wherein the non-linear relationship comprises a polynomial component, preferably of degree two.

46. The patient interface of any one of claims 43 to 45, wherein the at least one outflow vent is configured to generate in use, a predetermined exhaust flow rate for a predetermined supply flow rate.

47. The patient interface according to any one of claims 43 to 46, wherein the at least one outflow vent is configured to generate in use a predetermined interface pressure and an associated exhaust flow rate for a predetermined supply flow rate.

48. The patient interface according to any one of claims 43 to 47, wherein a total cross sectional area of the at least one outflow vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

49. The patient interface according to any one of claims 43 to 48, wherein the patient interface comprises at least one gas delivery element configured to provide the gases flow into the nares of the patient, and the at least one outflow vent comprises:

- at least one opening in at least one insert locatable in the nare around the nasal prong.

50. The patient interface according to claim 49, wherein the at least one insert is provided separately from the patient interface.

51. The patient interface according to any one of claims 43 to 50, wherein the patient interface comprises at least one gas delivery element configured to provide the gases flow into one or both of the patient's nares.

52. The patient interface according to any one of claims 43 to 51, wherein the sealing element comprises at least one nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare.

53. The patient interface according to any one of claims 49 to claim 52, wherein the sealing element is integrated with or into the gas delivery element and optionally, wherein the sealing element comprises the at least one outflow vent.

54. The patient interface according to any one of claims 43 to 53, wherein the patient interface comprises a body portion comprising the at least one outflow vent.

55. The patient interface according to claim 54, wherein the body portion comprises a chamber between a gases inlet to the patient interface and the patient, the chamber comprising a restriction causing asymmetrical flow to the patient's nares.

56. The patient interface according to any one of claims 43to 55, wherein the patient interface comprises a gases delivery side member comprising a collapsible portion that closes or partially closes to reduce or stop flow through the first patient interface.

57. The patient interface according to claim 56, wherein the collapsible portion is configured to collapse upon application of a force arising from placement of a respiratory mask over the patient interface.

58. The patient interface according to any one of claims 43to 57, wherein the at least one outflow vent is sized to allow provision of a gases flow from the respiratory mask to the patient.

59. The patient interface according to claim 57 or claim 58, wherein the respiratory mask comprises a bag valve mask.

60. The patient interface according to any one of claims 43 to 59, wherein the patient interface is configured to generate an asymmetrical flow profile into the patient's nares.

61. The patient interface according to any one of claims 43 to 60, wherein the patient interface is configured to receive side entry of gases, preferably single side entry.

62. The patient interface according to any one of claims 43 to 61, comprising at least one sampling port.

63. The patient interface according to claim 62, wherein the at least one sampling port is couplable with or provides a gas sampling line to provide fluid communication of gases in the patient interface to at least one sensor, optionally wherein the at least one sensor comprises a pressure, temperature, gas composition, CO2 or humidity sensor.

64. The patient interface according to any one of claims 43 to 63 comprising at least one gas sampling conduit that is adjustable to locate a sampling tip at an oral region of the patient when in use.

65. The patient interface according to claim 64, wherein the gas sampling conduit is attachable such as removably attachable, to the patient interface.

66. The patient interface according to any one of claims 43 to 65, comprising at least one access port that is normally closed and is openable to provide instrument access to the nasal cavity via the patient interface.

67. The patient interface according to claim 66, wherein the access port comprises a removable cover and optionally, wherein the removable cover comprises one or more of the at least one outflow vent.

68. The patient interface according to any one of claims 43 to 67, wherein the patient interface comprises a headgear connector to stabilise the patient interface on the patient when in use.

69. The patient interface according to any one of claims 43 to 68, wherein the patient interface comprises a retention mechanism configured to improve sealing by the sealing element.

70. The patient interface according to any one of claims 43 to 69, wherein the at least one outflow vent is configured to generate in use, a pressure differential between the patient and atmosphere comprising about 7cmH2O to about 15cmH2O at a supply flow rate of about 70 L/min.

71. The patient interface according to any one of claims 43 to 70, wherein the at least one outflow vent is configured to generate exhaust rates from the patient interface substantially corresponding to a supplied flow rate of gas while the patient's mouth is closed and during breath hold or while the patient is apnoeic.

72. The patient interface according to any one of claims 43 to 71, wherein the at least one outflow vent is non-variable.

73. The patient interface according to any one of claims 43 to 72, wherein the at least one outflow vent comprises a cross sectional shape comprising a circle, ellipse, oval, obround, quadrilateral, or squircle.

74. The patient interface according to any one of claims 43 to 73, wherein the at least one outflow vent comprises 1 or 2 or 3 or 4 or 5 or 6 discrete openings.

75. The patient interface according to any one of claims 43 to 74, wherein the at least one outflow vent comprises 6 discrete openings each having a cross sectional dimension of about 3 mm.

76. The patient interface according to any one of claims 43 to 75, wherein the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape.

77. The patient interface according to any one of claims 43 to 76, wherein the at least one outflow vent comprises at least one small opening and at least one large opening.

78. The patient interface according to claim 77, wherein the at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm.

79. The patient interface according to claim 77 or claim 78, wherein the at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about 1 mm to about 2 mm or about 2 mm to about 3mm.

80. The patient interface according to any one of claims 77 to 79, wherein a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

81. The patient interface according to any one of claims 77 to 80, wherein when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening.

82. The patient interface according to any one of claims 77 to 81, wherein when in use, flows from the at least one small opening are directed towards the patient's mouth.

83. The patient interface according to any one of claims 77 to 82, wherein when in use, flows from the at least one large opening are directed away from the patient's mouth.

84. The patient interface according to any one of claims any one of claims 43 to 83, wherein the patient interface is configured to generate an interface pressure during provision of the respiratory support.

85. The patient interface according to any one of claims 43 to 84, wherein the at least one outflow vent is shaped to generate transitional or turbulent flow characteristics, preferably at flow rates above about 50 LPM.

86. The patient interface according to any one of claims 43 to 85, wherein the interface pressure comprises mean interface pressure.

87. The patient interface according to any one of claims 43 to 86, wherein the rate of change is an average rate of change.

88. The patient interface according to any one of claims 43 to 87, wherein the rate of change is determined in the absence of effects from patient breathing.

89. The patient interface according to any one of claims 43 to 88, comprising a vent member comprising the at least one outflow vent.

90. The patient interface according to claim 89, wherein the vent member is removable to provide instrument access to the nasal cavity via the patient interface.

91. A method of providing respiratory support to a patient, the method comprising:

- using a first patient interface to provide a first respiratory support to the patient;

- placing a second patient interface over the first patient interface to reduce or stop flow of the first respiratory support to the first patient interface; and

- providing a second respiratory support using the second patient interface; wherein the first patient interface comprises at least one vent sized such that the second respiratory support from the second patient interface can be provided to the patient via the first patient interface.

92. The method according to claim 91, wherein the first patient interface comprises at least one nasal prong configured to provide the first respiratory support into at least one of the patient's nares.

93. The method according to claim 91 or claim 91, wherein the first patient interface comprises at least one sealing element comprising a nasal pillow, prong, cushion, cuff or cradle configured to form a substantial seal with the patient's nare to substantially limit escape of gases except via the at least one vent.

94. The method according to any one of claims 91 to 93, wherein the first patient interface comprises a body portion comprising the at least one vent.

95. The method according to any one of claims 91 to 94, wherein the first patient interface comprises a gases delivery side member comprising a collapsible portion that closes or partially closes to reduce or stop flow through the first patient interface.

96. The method according to claim 95, wherein the collapsible portion is configured to collapse upon application of a force arising from placement of the second patient interface over the first patient interface.

97. The method according to any one of claims 91 to 96, wherein the first respiratory support comprises:

- controlling the gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one vent at a first exhaust flow rate; and

- controlling the gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a second rate of change in the second interface pressure associated the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with the first exhaust flow rate.

98. The method according to any one of claims 91 to 97, wherein the at least one vent is configured to provide:

- a first predetermined resistance to flow in use in a range of greater than about 0 cmH20/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.05 cmH2O/Lmin-l to about 0.15 cmH2O/Lmin-l, or about 0.1 cmH2O/Lmin-l to about 0.15 cmH20/Lmin-l for a first exhaust flow rate value that is in a range of more than about 0 LPM to about 40 LPM, or about 30 LPM to about 40 LPM or about 35 to about 45 LPM; or when the supply flow rate is below 15 LPM; and

- a second predetermined resistance to flow in use in a range of greater than about 0.15 cmH2O/Lmin-l to less than about 0.5 cmH2O/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.4 cmH20/Lmin-l, or about 0.2 cmH20/Lmin-l to about 0.3 cmH20/Lmin-l for a second exhaust flow rate value that is in a range of more than about 40 LPM to about 100 LPM, or about 40 LPM to about 70 LPM, or about 40 LPM to about 60 LPM, or about 50 LPM to about 70 LPM, or about 50 PM to about 60 LPM, or about 60 LPM to about 70 LPM.

99. The method according to any one of claims 91 to 98, wherein the first respiratory support comprises providing a flow of gases at a supply flow rate to the patient interface and generating an interface pressure and an exhaust flow through the at least one vent at an exhaust flow rate, wherein values of interface pressure and values of exhaust flow rate comprise a non-linear relationship comprising a polynomial.

100. The method according to claim 99, wherein the non-linear relationship comprises a polynomial component, preferably of degree two.

101. The method according to any one of claims 98 to 100, wherein for a given exhaust flow rate, the resistance to flow is attributable to the size and/or shape of the at least one vent.

102. The method according to any one of claims 91 to 101, wherein a total cross sectional area of the at least one vent is in a range of about 20 to about 100 mm², or about 35 mm² to about 80 mm² or about 35 mm² to about 60 mm², or about 35 mm² to about 50 mm², or about 35 mm² to about 40 mm², or about 35 mm² to about 45 mm².

103. The method according to any one of claims 91 to 102, wherein the method comprises the step of locating the first patient interface, comprising at least one nasal sealing element, on the patient.

104. The method according to any one of claims 91 to 103, wherein the method comprises the step of removing the second patient interface to resume providing the first respiratory support.

105. The method according to any one of claims 91 to 104, wherein the second patient interface comprises a vent or expiratory path for exhausting gases.

106. The method according to any one of claims 91 to 105, comprising the step of alternating between the first respiratory support and the second respiratory support by removal or application of the second patient interface.

107. The method according to any one of claims 91 to 106, wherein the second respiratory support is provided to achieve one or more of:

- increase in patient oxygenation;

- delivery of one or more substances to the patient's airway;

- change in interface pressure;

- change in gases flow rate;

- different control over interface pressure; and

- different control over gases flow rate.

108. The method according to any one of claims 91 to 107, wherein the at least one vent is non-variable.

109. The method according to any one of claims 91 to 108, wherein the at least one vent comprises a cross sectional shape comprising a circle, ellipse, oval, obround, quadrilateral, or squircle.

110. The method according to any one of claims 91 to 109, wherein the at least one vent comprises 1 or 2 or 3 or 4 or 5 or 6 discrete openings.

111. The method according to any one of claims 91 to 110, wherein the at least one vent comprises 6 discrete openings each having a cross sectional dimension of about 3 mm.

112. The method according to any one of claims 91 to 111, wherein the at least one vent is shaped to generate transitional or turbulent flow characteristics, preferably at flow rates above about 50 LPM.

113. The patient interface according to any one of claims 91 to 112, wherein the at least one outflow vent comprises a plurality of openings not all having the same size and/or shape.

114. The patient interface according to any one of claims 91 to 113, wherein the at least one outflow vent comprises at least one small opening and at least one large opening.

115. The patient interface according to claim 114, wherein the at least one small opening has a cross sectional dimension less than about 1 mm, preferably less than about 0.75 mm, or about 0.5 mm, or about 0.3 to 0.7 mm.

116. The patient interface according to claim 114 or claim 115, wherein the at least one large opening has a cross sectional dimension greater than about 1 mm or greater than about 2 mm such as about 1 mm to about 2 mm or about 2 mm to about 3mm.

117. The patient interface according to any one of claims 114 to 116, wherein a total cross sectional area of the at least one small opening is similar to a total cross sectional area of the at least one larger opening.

118. The patient interface according to any one of claims 114 to 117, wherein when in use, flows from the at least one large opening are directed in a direction that is different from a direction of flows from the at least one small opening.

119. The patient interface according to any one of claims 114 to 118, wherein when in use, flows from the at least one small opening are directed towards the patient's mouth.

120. The patient interface according to any one of claims 114 to 19, wherein when in use, flows from the at least one large opening are directed away from the patient's mouth.

121. The method according to any one of claims 91 to 120, wherein the second patient interface comprises a mask.

122. The method according to any one of claims 91 to 121, wherein the second patient interface comprises a bag valve mask.

123. The method according to any one of claims 91 to 122, wherein the interface pressure comprises mean interface pressure.

124. A system for providing respiratory support to a patient, the system comprising:

- a patient interface system for providing a flow of gases to the patient, the patient interface system having at least one outflow vent; and

- a gases source controllable to: provide a gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; and provide a gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a first predetermined resistance to flow of the at least one outflow vent at the first exhaust flow rate is different than a second predetermined resistance to flow of the at least one outflow vent at the second exhaust flow rate.

125. A system for providing respiratory support to a patient, the system comprising:

- a gases source controllable to: provide a gases flow at a first supply flow rate and generating a first interface pressure and an exhaust flow through the at least one outflow vent at a first exhaust flow rate; and provide a gases flow at a second supply flow rate and generating a second interface pressure and an exhaust flow rate through the at least one outflow vent at a second exhaust flow rate; wherein a second rate of change in the second interface pressure associated with a change in the second exhaust flow rate is greater than a first rate of change in the first interface pressure associated with a change in the first exhaust flow rate.

126. A system for providing respiratory support to a patient, the system comprising:

- a first patient interface for providing a first respiratory support to the patient, the first patient interface comprising at least one vent sized to allow a second respiratory support to be provided to the patient while flow of the first respiratory support to the first patient interface has been reduced or stopped;

- one or more flow sources providing a gases flow for one or both of the first respiratory support and the second respiratory support; and

- a controller for controlling the one or more flow sources