GB2248783A - Regulating the cuff pressure of an endotracheal tube - Google Patents

Abstract

An inflatable cuff 2 of an endotracheal tube 1 is maintained at a constant pressure differential above the varying airway passage pressure by a pressure regulator 10 at the outlet 6 from a breathing gas source 7, the regulator including a differential pressure valve with an inlet 13 from the source 7, an outlet 14 to the tube 1 and a further outlet 22, upstream of the valve disc 17 and connected by a tube 3 to the cuff. The pressure differential may be fixed (Fig 2) or adjustable by rotating an adjustable seat 20 of the control spring 18. <IMAGE>

Description

PRESSURE REGULATOR FOR THE CUFF OF AN ENDOTRACHEAL TUBE.

Field of Search: 128/207.15,207.16, 128/207.14, 205.24; 604/96-99.

References Cited: U.S. PATENT DOCUMENTS 3,529,596 9/1970 GARNER .................. 128/207.15 3,931,822 1/1976 MARICI .................. 128/207.15 4,090,518 5/1978 ELAM .................. 128/207.15 4,119,101 10/1978 IGICH .................. 128/207.16 4,178,938 12/1979 AU .................. 128/207.15 4,285,340 8/1981 GEZARI ET AL. 128/207.15 4,471,775 9/1984 CLAIR ET AL. ........... 128/207.15 4.495,948 1/1985 SHAPIRO ........... 128/207.15 4,501,273 2/1985 McGINNIS ........... 128/207.15 4,565,194 1/1986 WEERDA ET AL. ........... 128/207.15 4,825,862 5/1989 SATO ET AL. ........... 128/207.15 4,850,349 7/1989 FARAHANY ........... 128/207.15 EUROPEAN PATENTS 0143618 6/1985 EUROPEAN PAT. OFF. 128/207.15 3435900 4/1986 FED. REP. OF GERMANY 128/207.15 JAPANESE PATENT 62-8766 1/1987 JAPAN.

BACKGROUND OF THE INVENTION This invention relates generally to the technique of controlling pressures within cuffed endotracheal tube systems, and more particularly to a simple apparatus for the maintenance of a constant pressure difference between the pressure inside the cuff of an endotracheal tube which should be greater than the airway pressure, that is the pressure within the lumen of the endotracheal tube.

PRIOR ART During positive pressure ventilation of a patients lungs while administering anaesthetic gases or in the intensive respiratory care unit, a tube is necessarily inserted into the trachea (referred to as an endotracheal tube). Inorder to prevent gas escaping past the endotracheal tube, a relatively large volume soft ring-shaped hollow collapsible bag known as the "cuff" is attached to the outer surface of the endotracheal tube at the tracheal end of the tube. This bag or cuff is inflated with air so that it forms an air tight seal with the mucosal walls of the trachea. It also anchors the tracheal tube within the trachea below the vocal cords.

It is usual practise to inflate the cuff to a pressure which is greater than airway pressure inorder to prevent leakage of gas past the cuff. This practise frequently results in much higher pressures than the peak inflation pressures used for ventilation.

Possible reasons for this include: quick and careless initial over inflation while using a syringe for the purpose; air that is injected at room temperature may warm up to body temperature causing the fixed volume within the cuff to expand; the use of anaesthetic gases such as nitrous oxide may diffuse into the cuff. Excessive cuff pressures may affect perfusion (the blood supply) to the mucosal lining of the trachea causing damage. The higher the pressures used the poorer the perfusion that results and the greater the risk of causing permanent damage.

It would be obviously advantageous therefore to use a system that ensures that the lowest cuff pressures necessary are used to achieve the desired objective, namely the sealing of the endotracheal tube. The ideal would be a system that automatically held the cuff pressure just above airway pressure, i.e. one which allows for the variation of airway pressure to be transmitted to the cuff.

A number of designs varying in complexity which aim to achieve this ideal have been described. For instance the most relevant of many applications (see references cited) include U.S. patent application serial numbers 4850349 and 4825862.

Serial no. 4850349 describes a simple device not requiring an external gas supply to power the device, but still suffers from all the problems related to fixed cuff volume devices, namely it is possible to over inflate the device, nitrous oxide may diffuse into the system, there is no compensation for small leaks and specific to the device is that it will work only with a limited range of cuff volumes or sizes.

Serial no. 4825862 describes a somewhat more elaborate device which does appear to achieve the desireable characteristics, however because it is more elaborate it is more bulky/heavy and expensive. It also requires an external high pressure gas source to power the device.

SUMMARY OF THE INVENTION In accordance with the present invention, a simple apparatus is provided which alllows for the safe, reliable and automatic control and maintenance of endotracheal tube cuff pressure by a preset or an adjustable level above airway pressure during positive pressure ventilation. This automatically achieves the minimum level of cuff pressure necessary to ensure a proper seal for an endotracheal tube thereby minimising the complications of an over pressurised cuff which may include: sloughing of the tracheal mucosa, fistula formation and stenosis.

A pressure regulator powered by the gas supply source to a breathing system for the maintenance of a constant pressure difference in a cuffed endotracheal tube above airway pressure during positive pressure ventilation comprising a tubular connecting means for attachment and interposition between the gas supply machine and the breathing system and connected to the cuff inflation port of an endotracheal tube, the said connecting means comprising a tubular threshold valve for the purpose of generating a constant pressure difference when gases supplying the breathing system flow through the said valve, the pressure differential created by the said threshold valve being either fixed or adjustable, with upstream connecting means for attachment to and in open communication with the inside of the cuff of an endotracheal tube for the purpose of transmitting and maintaining the said upstream pressure to the said cuff above that of the airway pressure by a constant value equal to the threshold valve setting.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 schematically illustrates the overall system in accordance with the use of this invention, the position of the cuff pressure regulator and its attachment to an anaesthetic machine and the breathing system, and its connection to the pilot tube of the endotraheal tube cuff.

Fig.2 and Fig.3 schematically illustrates longitudinal sections of two preferred embodiments of the pressure regulator, a fixed pressure differential regulator and an adjustable differential pressure regulator respectively, in accordance with the present invention.

DETAILED DESCRIPTION OF THE NUMBERED DRAWINGS Fig.1 shows an anaesthetic gases supply machine 7 with outlet from the machine 6 to which is attached a cuff pressure regulator 10 of the present invention, which in turn is attached both to the pilot tube 3 of an endotracheal tube 2 by means of an upstream tubular attachment site 22 of regulator 10 and at the said regulators outlet to the inlet of a breathing system 4a.A breathing system 4, with inlet 4a, is shown to be attached to an endotracheal tube 1 at the tracheal end of which is the attached endotracheal tube cuff 2, which is maintained inflated with gas, i.e. in a pressurised state, by means of a pilot tube 3 which is attached to and in open communication with the said regulator 10 via the said tubular connection site 22. the breathing system may be pressurised intermittently to achieve positive airway pressure ventilation by a ventilating means (in this instance a mechanical ventilator 5).

Fig.2 schematically illustrates a longitudinal section of a preferred embodiment of a simple fixed differential pressure regulator in accordance with the present invention. To explain its use in context, reference shall occasionally be made to Fig.1.

The cuff pressure regulator 10, hereinafter referred to as the regulator or by reference numeral 10, is attached to the outlet of an anaesthetic gas supply machine 6 in Fig.1 by means of port,13, the inlet to the regulator,10, with sealing surface,11, forming a gas tight seal push fit on to the said outlet,6, in accordance with the ISO 22mm male to female standard fittings.Z The anaesthetic supply gases are permitted to flow through a spring-loaded valve with a constant opening pressure comprising: A partition 19 to separate an upstream channel 13 from the downstream outlet channel 14 of the said regulator, at least one channel 15 within the partition through which the anaesthetic gases must flow.

On the downstream side of the said partition 19 there is provided a valve seating edge 19a with a wider diameter than the collective span of channels 15 which surround a central core of the said partition 19 with a central channel 19b (see partition 19 removed from the valve fro clearer view) for the free movement of an axial stabilising rod 16 to slide within.

A valve seat 17 with central axial stabilising rod 16 which is permitted to slide freely through the said central channel (or aperture) 19b the said valve 17 capable of forming a gas tight seal (under conditions of zero flow) when in apposition with the said sealing edge 19a.

A spring 18, which may comprise a conventional spring or a dumbell shaped synthetic rubber (e.g. silicone rubber or other elasomeric substance) bent into a "U" shape (shown in Fig.2) to provide a constant force on the clip 20 which is attached to the end of the stabilising rod 16 of the said valve seat 17 which in turn is therefore held by the same force against the sealing edge 19a.

The regulator 10 necessarily includes port 21 which allows for open communication with upstream channel 13 and a facility for the attachment of a tube 22 to allow for connection by a light non-distensible tubing to pilot tube 3 in fig.1 thereby allowing free flow of the supply gases between channel 13 and the inside of the endotracheal tube cuff 2 in fig.1.

The outlet (downstream) portion of the regulator 10 comprises a channel 14 with external sealing surface 15 inaccordance with the ISO standard 15mm female and 22mm male tapered fittings for attachment to an anaesthetic breathing system.

Fig.3 schematically illustrates a longitudinal section of a preferred embodiment of an adjustable constant differential pressure regulator in accordance with the present invention. To explain its use in context, reference shall occasionally be made to Fig.1.

The cuff pressure regulator 10, hereinafter referred to as the regulator or by reference numeral 10, is attached to the outlet of an anaesthetic gas supply machine 6 in Fig.l by means of port,13, the inlet to the regulator,10, with sealing surface,ll, forming a gas tight seal push fit on to the said outlet,6, in accordance with the ISO 22mm male to female standard fittings.Z The anaesthetic supply gases then flow through a spring loaded valve with an adjustable, constant opening pressure comprising: A partition,19, to separate an upstream channel,13, from the downstream outlet channel,14, of the said regulator, a channel 15 within the partition through which the anaesthetic gases must flow.

On the downstream side of the said partition 19 there is provided a valve seating edge 19a with a diameter which is wider than channel 15.

A valve seat 17 with central aperture 17a is provided through which a central axial stabilising rod or pin 16 freely passes and which is firmly attached to the differential pressure control 20.

The said valve seat 17 is able to move freely over the stabilising rod 16, the precise diameter of the said rod or pin exactly matching the aperture 17a so as to allow smooth movement of the valve seat 17 with minimal gas leak between the sliding edges of aperture 17a and the stabilising rod. The purpose of the stabilising rod is to ensure that the valve seats nicely on the sealing edge 19a.

A conventional spring 18 of suitable tensile strength is held under the desired and adjustable amount of tension being compressed between the said valve seat 17 and the differential pressure control adjustment 20, with 18 and 20 located downstream from the partition 19.

The differential pressure control adjustment 20 comprises a screw thread, a control knob 20 and a sealing "O" ring as shown in fig.3. with rotation of the control knob resulting in outward or inward movement thereby varying the tension of the said spring 18.

The regulator 10 necessarily includes port 21 which allows for open communication with upstream channel 13 and a facility for the attachment of a tube 22 to allow for connection by a light non-distensible tubing to pilot tube 3 in fig.1 thereby allowing free flow of the supply gases between channel 13 and the inside of the endotracheal tube cuff 2 in fig.1.

The outlet (downstream) portion of the regulator 10 comprises a channel 14 with external sealing surface 15 inaccordance with the ISO standard 15mm female and 22mm male tapered fittings for attachment to an anaesthetic breathing system.

IN USE (refer to fig.l.) The regulator 10 is connected to the outlet 6 of the anaesthetic gas supply machine 7 and the regulator inturn is attached to the inlet of the breathing system 4a, the breathing system 4 is inturn attached to an endotracheal tube 1 and a means for ventilating such as a mechanical ventilator 5, for the purpose of achieving positive pressure ventilation.The upstream portion 13 of the regulator 10 is also connected by means of said port 21 and tube attachment site 22 via an extension of the pilot tube 3 to the inside of the cuff 2, so that, when anaesthetic gas flows through the regulator into the anaesthetic breathing system 4, a constant pressure difference is maintained between the upstream 13 and the downstream portion 14 of the regulator; the upstream higher pressure being maintained and transmitted to the endotracheal tube cuff 2 with the said downstream portion being in direct communication with the breathing system 4 and therefore the endotracheal tube 1 or airway pressure.

A rise in airway pressure, when positive pressure is generated by the ventilator during the inspiratory phase of controlled ventilation, results in an equal rise of pressures within the regulator 10. As the supply gas continues to flow across the said regulator valve, the pressure differential across the regulator remains unchanged and therefore any rise in downstream pressure is transmitted to the upstream section which inturn is transmitted by means of the appropriate flow of gas from 13 via 21, 22, 3 and into the endotracheal tube cuff 2. The said cuff pressure therefore is continuously held above airway pressure by the regulator 10.

A fall in airway pressure such as occurs during the passive expiratory phase results in a proportionate fall in pressure in the regulator 10 which in turn allows for anaesthetic gases which accumulated in the cuff during the inspiratory phase to flow outwards, through 3, 22, 21 and into 13 i.e. depressurisation of cuff pressure to a value equal to the opening pressure set across the valve of the regulator 10.

It may be appreciated from the aforesaid that the volume in the endotracheal tube cuff 2 is continuously changing so as to allow for the equalisation of pressures within the system apart from the specific pressure difference set across the regulator 10.

It may be appreciated that this particular invention is noval in its simplicity being powered by anaesthetic gases supplying the breathing system. It overcomes the problems of constant cuff volume devices. It also overcomes one potential hazard of any device powered by an external high pressure gas source, namely, that the high pressure gas source may by some means be transmitted to the cuff and a safety blow off pressure release valve may therefore be necessary. No such safety release valve is required in this invention.

Although the invention has been described by referring to a preferred embodiment, numerous modifications are possible in parts and construction without departing from the scope of the invention as disclosed and claimed herein.

Claims (1)

1. What is claimed is:

   CLAIM 1 A pressure regulator powered by the supply gases to a breathing system for the maintenance of a constant pressure difference during anaesthesia or any circumstance needing respiratory support comprising, a tubular connecting means for attachment and interposition between the gas supply machine and the breathing system with a connection to the cuff inflation port of an endotracheal tube, the said connecting means comprising a spring loaded valve set at an appropriate constant opening pressure resulting in an upstream valve pressure constantly raised above the pressure in the breathing system and an upstream from the said spring loaded valve port I connecting means in open communication with the inside ti the cuff of an endotracheal tube for the purpose of transmitting and maintaining the said upstream pressure to the said cuff above that of the airway pressure by a constant value equal to the threshold valve setting.

   CLAIM 2 A pressure regulator as set forth in claim 1 where the said spring loaded threshold valve uses a dumbell shaped rubber spring as desc ribbed in the specification.

   CLAIM 3 A pressure regulator as set forth in claim 1 where the said valve opening pressure may be varied by means of adjustment of the tension of the spring in a spring loaded threshold valve.

   CLAIM 4 A pressure regulator as set forth in any of the preceeding claims which may form part of a respiratory support apparatus such as a gas supply machine, a ventilator, an automatic mechanical respiratory pump or breathing system.