SE538864C2 - Method System and Software for Protective Ventilation - Google Patents

Description

538 864 mechanics (e.g. total elastance), rather than measuring lung mechanics (e.g. lung elastance) separately. A limitation of existing breathing apparatus and associated ventilation strategies is that they do not provide a way for the user to avoid a strategy that may cause V|L| or to ensure that a strategy will not result in an end inspiratory transpulmonary pressure (PTPH) that is below a pre- determined maximum value. Another drawback of existing systems and methods for ventilation is that, PTP is measured using esophageal pressure as a surrogate for pleural pressure.

WO 2011/157855 Al, which is incorporated by reference in its entirety for all purposes, especially equations 1-17 and their descriptions on pages 7-14, discloses that it is possible to calculate an estimated transpulmonary pressure after measuring lung elastance as the ratio of change in end- expiratory airway pressure (APEEP) to change in end-expiratory lung volume (AEELV), APEEP/AEELV following a PEEP step maneuver. WO 2011/157855 does not disclose systems comprising graphic visualizations based upon calculated values of lung elastance.

During ventilation of a patient clinicians often seek to maintain a certain ventilation strategy for a treatment which is believed particularly advantageous for a ventilated patient. WO 2014/124684 A1, which is incorporated by reference, in particular Figs. 3-9 and their corresponding descriptions, discloses a breathing apparatus with a ventilation strategy tool comprising a graphic visualization tool that provides a combination of a target indication one or more ventilation related parameters of a ventilation strategy and a reciprocating animation of parameter(s) relative the target indication, which may be based upon user input. WO 2014/124684 does not disclose calculating values for lung elastance or using such values for avoiding V|L|.

There is hitherto no flexible tool to provide clinicians with a status of an on-going ventilation in a clear and easily understandable way when it comes to the crucial point of how the current patient ventilation is related to a chosen ventilation strategy. lt would be particularly desirable for such a tool to be adaptable to the status an on-going ventilation of a patient during the ventilation itself.

Also, it would be desired if the tool provided a feedback to the clinician that can be understood from a distance from a breathing apparatus. lt would be desired, for instance, to provide a quick overview of a current ventilation strategy to the clinical user. Each ventilation strategy has a target. A quick identification of compliance of an ongoing ventilation with this target to the clinical user would be desired and allow for faster clinical decision taking related to the ventilation strategy. For instance, a patient in an isolation room or during an x-ray examination might not be approached by the clinician with undue burden. Thus, such a tool would be advantageous if it provided the clinician with a current status of a ventilation in relation to a desired strategy, even for a projected outcome of adjustments to clinical ventilation parameters, e.g. in a simulated ventilation. 538 864 For instance for education of clinicíans, it would be advantageous if this tool was provideable without a patient connected to the breathing apparatus, e.g. in a simulated ventilation, e.g. based on a test lung connected to the breathing apparatus. Hence, there is a need for such a tool implemented in a system including a breathing apparatus that can provide the ventilation, and based on adjustments thereof pursues the desired ventilation strategy. Clinical decisions related to the treatment of a ventilated patient might then be facilitated. Based on a target input from a clinical user, the breathing apparatus may automatically adjust remaining ventilation parameters for safe and reliable ventilation ensuring sufficient oxygenation of a connected patient. A corresponding method, software and system are provided. Treatment of the ventilated patient may thus be improved. Cost of care can potentially reduced by the more effective treatment that can be provided related to the chosen ventilation strategy.

Thus, an improved breathing system for providing a clinical tool providing clear and easily understandable status for an on-going ventilation strategy in relation to a desired outcome thereof would be advantageous. This need and the above-mentioned limitations of the current state of the art are addressed by the current disclosure, wherein the present invention provides an improvement over the state of the art in the field of breathing apparatus and ventilation.

Brief Summary of the lnvention The invention is defined in the appended independent patent claims, wherein specific exemplary embodiments are defined in the dependent claims. ln one aspect, the present disclosure includes is a system comprising a breathing apparatus, a display unit and a processing unit operatively connected to the display unit and configured to provide a graphical visualization on the display unit including information on transpulmonary pressure and lung volume, such as a pressure vs. volume curve, for a patient connected to the breathing apparatus.

The graphical visualization may alternatively or additionally include an indication of tidal volume (VT), positive end-expiratory pressure (PEEP), end-inspiratory transpulmonary pressure (PTPE. or PTPEI), end-expiratory lung volume (EELV), and/or end-inspiratory lung volume (EILV). The graphical visualization may alternatively or additionally include breath-by-breath change in EELV. ln one embodiment, the graphical display comprises a total lung volume vs. pressure graph in which PEEP = PTPEE. ln another aspect, the disclosure includes a decision support system comprising a breathing apparatus, a display unit and a processing unit operatively connected to the display unit, wherein the 538 864 processing unit is configured to provide on the display unit a graphical visualization including a combination of VT, PEEP, and PTPEI. The graphical visualization may alternatively or additionally include an indication of EELV, EILV, and/or breath-by-breath change in EELV. Decision support may be automated prevent and/or alert an operator to the setting of operational parameters of the breathing apparatus that are calculated to result in a PTPEI above a pre-determined value, for example to prevent VILI. Additionally or alternatively, the decision support system may provide a graphic visualization that draws the attention of an operator to one or more parameter settings that are calculated to result in a PTPEI above a pre-determined value, for example to prevent VILI.

Decision support may comprise a graphic representation of a ventilation strategy, for example in the form of PEEP and VT settings to be entered by a user.

In yet another aspect, the disclosure includes a computer-readable medium comprising a computer program for processing by a processing unit for providing the graphical visualizations of one or both of the first two aspects of the disclosure.

The invention is based upon an estimation, or calculation, of lung elastance rather than an estimation of the total elastance, in which lung elastance and chest wall elastance are combined. The selection of pressures and volumes delivered by the ventilator are thereby strictly adapted to the condition of the lung as opposed to a combination of lung and chest wall mechanics. ln one aspect, the invention provides a method for obtaining a complete lung volume / lung pressure curve or lung pressure curve /lung volume (V/PTP or PTP/V curve) from end-expiration at functional residual capacity to end- inspiration of the highest PEEP level of a PEEP trial and to identify lower and upper inflection points.

This method, which provides estimated values for Lung Elastance (EL) can be performed in less than 5 minutes, making it possible to provide a breath-by-breath PTP versus time curve in the form of a visual display that is easily interpretable by an operator of a ventilator. The combination of the complete lung PTP/V curve and the tidal PTP/V ([PTP/VT]) curve can be used to adjust both tidal volume and PEEP level to minimize the risk of lung tissue damage in the individual patient. A lung or lungs may be used to refer to the lung or lungs of a human or non-human patient or to a test lung, model lung, or artificial lung.

Brief Description of the Drawings Fig. 1A and B are examples of V/P graphs that may be used to estimate of AEELV between ZEEP/FRC and baseline clinical PEEP; Figs. 2A-C are graphs of breath by breath change in EELV after a PEEP change plotted on a logarithmic scale; 538 864 Fig. 3 is an example of a graph showing breath by breath airway, esophageal and transpulmonary pressure volume curves during a PEEP trial from ZEEP to 16 cmHzO; Figs. 4A and B are graphical displays of airway pressure and EELV measurements breath-by-breath AEELV, measurments; Figs. 4C and D are graphic displays of breath-by-breath changes in EELV for low inlflection and high inflection zones; Figs. 5A and B are examples graphs of complete estimated lung P/V curves corresponding to pulmonary ARDS and extrapulmonary ARDS, respectively; Fig. 6A is graph of the complete PTP/V curve in a pulmonary ARDS patient; Fig. 6B is the same graph as Fig. 6A including system suggested PEEP and tidal volume settings that result in an end-inspiratory PTP that is below a predetermined maximum level; Fig. 7A is graph of a complete PTP/V curve in an extrapulmonary ARDS patient; and Fig. 7B is the same graph as 7A including system suggested PEEP and tidal volume that result in an end-inspiratory PTP that is below a predetermined maximum level.

Detailed Description of the lnvention The invention is based, in part, on the discovery that it is possible to obtain a PTP vs. volume curve (P/V curve) for a patient in a way that allows a breathing apparatus system and/or a user of such a system to quickly determine whether or not a selected combination of positive end-expiratory pressure (PEEP) and tidal volume (VT) will result in an end-inspiratory transpulmonary pressure (PTPE. or PTPEI) that is above a pre-determined limit, e.g. to prevent damage to the lungs. The inventors have discovered how to obtain a complete lung P/V curve using 1 or more PEEP steps, and furthermore, breath-by-breath.

Determination of end-expiratory lung volume changes, AEELV An incremental PEEP trial results in a "PEEP induced" inflation of the lungs. The increase in EELV following a PEEP increase can be calculated as the difference in EELV between two PEEP levels, where the EELV at each PEEP level is determined by a dilution method or by EIT (electric impedance tomography) or any method for determination of the absolute lung volume. However, a direct measurement of AEELV as by the ventilator pneumotachograph/spirometer is preferred for a rapid and accurate determination of AEELV.

Lung elastance (EL)and transpulmonary pressure (PTP) determination 538 864 The conventional method for determining EL and PTP is by using esophageal pressure measurements as a surrogate for pleural pressure, where PTP is the difference in tidal airway pressure and tidal esophageal pressure. Measurement of esophageal pressure is time consuming and there is no consensus on the interpretation of the absolute values or values in relation to atmospheric pressure.

As a consequence, only tidal variations in esophageal pressure are used. Also, the measurement of tidal esophageal pressure poses several obstacles. Measurements are sensitive to the filling of the balloon of the measurement catheter and position of the catheter. Several other factors have a detrimental effect on measurement results and all together precision is low. Thus, esophageal pressure measurements can be used for calculation of a lung P/V curve in the individual patient during a PEEP trial, but they are not preferred.

Total respiratory system elastance (EToT) is the difference in end-inspiratory airway plateau pressure and the end-expiratory airway pressure (APAW) divided by the tidal volume (VT), APAW/ VT.

Chest wall elastance (ECW) is the difference in end-inspiratory esophageal plateau pressure and the end-expiratory esophageal pressure (APES) divided by the tidal volume (VT), APES/ VT. Lung elastance (EL) is the difference between total respiratory system elastance and chest wall elastance, ETOT - ECW. Tidal transpulmonary pressure variation (APTP) is calculated as EL x VT. APTP of a tidal volume equal to the change in end-expiratory lung volume (VT=AEELV) is calculated as EL x AEELV.

By Lung Barometry The basic Lung Barometry concept is that lung elastance, EL, is equal to the change in PEEP divided by the corresponding change in end-expiratory lung volume, APEEP/AEELV. Thus, the determination of AEELV is an inherent part of the method. Airway pressure measurements are very precise and modern ventilators keep set PEEP levels constant. The AEELV following a PEEP change can be determined by the cumulative difference between inspiratory and expiratory tidal volumes. These AEELV measurements have a high precision (e.g. Fig. 4B). The determination of EL by Lung Barometry only demands a change in PEEP and a spirometric determination of the resulting AEELV. This is a very simple and precise method, which is much more suitable than esophageal measurement-based for determination of the lung P/V curve during a PEEP trial.

Total respiratory system elastance (ETOT) is the difference in end-inspiratory airway plateau pressure and the end-expiratory airway pressure (APAW) divided by the tidal volume (VT), APAW/ VT.

Chest wall elastance (ECW) is the difference between total respiratory system elastance and lung elastance, ETOT - EL, where ETOT is determined using a tidal volume equal to AEELV. Lung elastance 538 864 (EL) is the ratio of change in end-expiratory airway pressure (APEEP) to the corresponding change in end-expiratory lung volume (AEELV), APEEP/AEELV. APTP of a tidal volume equal to the change in end-expiratory lung volume (VT=AEELV) is by definition equal to the change in end-expiratory airway pressure (APEEP).

The basic measurement algorithm - Example Start from a steady state clinical PEEP level.

Increase PEEP by 70% of the APAW. The PEEP increase is preferably around 70% but may be greater or less than 70%, for example 30%, 40%, 50%, 60%, 80%, 90%, or 100%.

Determine the increase in EELV (AEELVup) as the cumulative difference between inspiratory and expiratory tidal volumes during = 1 minute, e.g. 30, 40, 45, 50, 55, 60, 65, 70, or 75 seconds. Return to baseline PEEP = 2 minutes after the increase in PEEP, for example 90, 100, 110, 120, 130, 140, or 150 seconds.

Determine the decrease in EELV (AEELVdown) as the cumulative difference between inspiratory and expiratory tidal volumes during = 1 minute.

Calculate the mean AEELV as (AEELVup + AEELVdown)/2.

Set the tidal volume to mean AEELV.

Determine total respiratory system elastance ETOT as APAW/VT=meanAEELv.

Calculate lung elastance (EL) as APEEP/AEELVmean.

Calculate chest wall elastance (ECW) as the difference between total respiratory system elastance and lung elastance, ECW = ETOT- EL.

Calculate the ratio EL/ETOT and calculate the ratio of EL to ETOT at the higher PEEP level as (ETOTHP - ECWgÛ/ Example - Determining PTP using basic Lung Barometry The end-expiratory PTP at baseline (PTPEEBL), clinical PEEP and baseline lung volume of zero is equal to the end-expiratory airway pressure (PEEP): PTPEEBL= PAWEEBL.

The end-expiratory PTP at the higher PEEP level (PTPEEHP) and a lung volume above baseline equal to AEELVmean is equal to the PEEP at the higher PEEP level: PTPEEHP = PAWEEHP.

The end-inspiratory PTP at baseline PEEP and a lung volume above baseline EELV equal to VTBLis PTPHBL = PTPEEBL + APAw X vTBL - Ecwß, X vTBL.

The end-inspiratory PTP at the higher PEEP level and a lung volume above baseline equal to AEELVmean + VTHP is PTPEIHP = PTPEEHP + APAWVTHP - ECWBL x VTHP.

ECW remains mainly constant when changing PEEP. 538 864 Example - Estimation of AEELV between ZEEP/FRC and baseline EELV Data of PTP at end-expiration and end-inspiration at baseline and the higher PEEP level is plotted versus corresponding EELV data. The best fit polynomial curve of the second and the third degree curve are plotted. The equation for the best fit curves are solved for zero PTP, which gives the mean volumes where the curves intersect with the volume axis at zero PTP. This estimated volume, AEELVO-BL, is added to all the previous EELV values, which means that EELVBL is equal to AEELVO-BL and that end-inspiratory lung volume at baseline lung volume is AEELVO-BL + VTBL. EELV at the high PEEP level is AEELVO-BL + AEELVBL-HP and the end-inspiratory lung volume at the high PEEP level is AEELVO-BL + AEELVBL-HP + VTHP.

The extended Lung Barometric measurement algorithm - Example The extended algorithm contains two consecutive PEEP steps, HP1 and HP2, still starting from a baseline clinical PEEP, but now reaching a higher lung volume and PTP.

The first increased PEEP level (PEEPHP1) is maintained only for a minute and AEELVBL-HPlup is determined as described for the basic algorithm.

The size of the second PEEP step is predicted as the difference in end-inspiratory plateau airway pressure between the high and the baseline PEEP levels, PAWEIHP1-PAWEEBL. AEELVHP1-HP2up is determined as described for the basic algorithm.

The second increased PEEP level (PEEPHP2) is maintained for a minute before returning PEEP to HP1.

AEELvHPl-HPZ clown and mean AEELvHPl-HPzup-down are determined as described for the basic algorithm.

EL between PEEPHPl and PEEPHP2 is determined as the difference in PEEP between HP2 and HP1 divided by the mean change in EELV between HPZ and HP1, APEEPHP1-HP2/AEELVHP1-HP2.

ETOT at HP2 is calculated as APAwHPz/VTHPZ.

ECW at HPZ is calculated as ETOTHP2-ELHP2.

A minute after lowering PEEP from HP2 to HP1, PEEP is lowered to baseline PEEP level. During the first minute after decreasing PEEP, AEELVBL-HP1down and meanAEELVBL-HP1 are determined as described for the basic algorithm.

The tidal volume is set to mean AEELVBL-HP1.

ETOT is determined as APAWBL/VTqneanAEELvBL-HP1.

EL is calculated as APEEP/AEELVmean BL-H P1.

ECW is calculated using ECWBL = ETOTBL - ELBL.

The ratio of EL to ETOT at baseline is calculated: ELBL/ETOTBL.

The ratio of EL to ETOT at PEEPHP1 is calculated: ELHPI/ETOTBP1. 538 864 The ratio of EL to ETOT at the PEEPHP2 is calculated: (ETOTHP2- ECWHP1)/ETOTHP2.

Example - Transpulmonary pressure by extended Lung Barometry ECW is assumed to remain essentially constant when changing PEEP.

The end-expiratory PTP at baseline (PTPEEBL), clinical PEEP and baseline lung volume of zero is equal to the end-expiratory airway pressure (PEEP); PTPEEBL = PAWEEBL.

The end-expiratory PTP at the higher PEEP level (PTPEEHP1) and a lung volume above baseline equal to AEELVmeanBL-HP1 is equal to the PEEP at PEEPHP1;PTPEEHP1 = PAWEEHP1.

The end-expiratory PTP at the highest PEEP level (PTPEEHP2) and a lung volume above baseline equal to AEELVmeanBL-HP1 + AEELvmeanHPl-HPZ is equal to the PEEP at PEEPHP2: PTPEEHP2 = PAWEEHP2 The end-inspiratory PTP at baseline PEEP and a lung volume above baseline EELV equal to VTBL is PTPEIBL = PTPEEBL + APAWVTBL - ECWBL x VTBL The end-inspiratory PTP at PEEPHPI and a lung volume above baseline equal to AEELVmean + VTHP is PTPEIHPI = PTPEEHPl + APAWVTHP1 - ECWHPl X VTHP1 The end-inspiratory PTP at PEEPHP1 and a lung volume above baseline equal to AEELVmean + VTHP is PTPEIHPZ = PTPEEHPZ + APAWVTHPZ - ECWH P2 X VTHP2 Example - Estimation of AEELV between ZEEP/FRC and baseline EELV by extended Lung Barometry Fig. 1 shows how EELV between a baseline PEEP and ZEEP/FRC can be determined without lowering PEEP to zero. Data of PTP at end-expiration and end-inspiration at baseline and PEEPHP1 and PEEPHP2 are plotted versus corresponding EELV data. A best fit polynomial of the second and third degree curve is plotted. The equations for the best fit curves are solved for zero PTP, which gives the mean volume where the curve intersects with the volume axis at zero PTP. This estimated volume, AEELVO-BL, is added to all the previous EELV values, which means that EELVBL is equal to AEELVO-BL and that end-inspiratory lung volume at baseline lung volume is AEELVO-BL + VTBL. EELV at PEEPHP1 is AEELVO-BL + AEELVBL-HP and the end-inspiratory lung volume at the high PEEP level is AEELVO-BL + AEELVBL-HP1 + VTHP1. The end-expiratory lung volume at PEEPH P2, EELVH P2 is AEELVO-BL + AEELVBL- HP1 + AEELVHP1-HP2 and the end-inspiratory lung volume at the high PEEP level is AEELVO-BL + AEELVBL-H P2 + VTHP2. Fig. 1A and B are graphs showing estimations of AEELV between ZEEP and baseline clinical PEEP. Fig. 1A shows a polynomial second degree best fit curve equation for the PTP/V points of the PEEP trial. Fig. 1B shows a polynomial third degree best fit curve equation for the PTP/V points of the PEEP trial. The mean of the values for the intercepts of the curves and the y-axis are used. For Fig. 1A and B the mean of the values is (301+180)/2 = 240 ml.

Example - Identification of inflection points/zones 538 864 The establishment of a new P/V equilibrium after increasing PEEP involves multiple breaths, where the lung volume increase decreases breath-by-breath until a new steady state is established. lf the volume increase (AEELV) of each breath is plotted on a logarithmic volume scale, an upwards convex (increasing lung elastance) or concave (decreasing lung elastance) or linear slope of lung elastance can be identified for the lung volume between the two PEEP levels. Figs. 2A-C are examples of log EELV vs. breath graphs that correspond to decreasing, increasing, and constant EL between two different PEEP levels.

Identification of non-linearity at a volume range between the end-inspiratory lung volume (EILV) of two PEEP levels Using the breath by breath end-inspiratory plateau airway pressure (PAWE|), an increasing EL is reflected in an increasing PAWEI after the first breath after PEEP is increased. lf the PAWEI decreases, EL decreases. lf PAWE| is constant, EL is constant at the highest volume levels. Fig. 3 shows an example of a type of graph that can be used to identify non-linearity in a volume range between the EILV at two PEEP levels. Breath by breath airway, esophageal and transpulmonary pressure volume curves during a PEEP trial from ZEEP to 16 cmH2O are shown. The progress of the PAWEI is circled.

During PEEP change from 4 to 8 cmH20, PAWEI decreases breath by breath, indicating a decreasing EL. During PEEP change from 8 to 12 cmH2O PAWEI remains mainly constant, indicating an unchanging EL. During PEEP change from 12 to 16 cmH2O PAWEI increases breath by breath, indicating an increasing EL (overdistension).

Example - Lung Barometric measurement display When a measurement procedure is intended to start, a measurement display appears on the screen.

Baseline airway pressures and tidal volumes are presented and steady state is determined. When PEEP is increased, the breath by breath increase in EELV is shown on a logarithmic scale to identify non-linearity, i.e. increase or decrease in EL between two PEEP levels (e.g. Figs. 2A-C). Additionally, the cumulative increase in EELV may displayed breath by breath and the AEELVup result is displayed (Fig. 4C). Figs. 4A and B show an illustrative example of such a display in which EL is 70 ml/cmH20, APTP/APAW at PEEP=5 cmH2O is 0.77, APTP/APAW at PEEP=15 cmH2O is 0.65, APEEPup and APEEPdown are each 10 cmH20, AEELVup is 680 ml, and AEELVdown is 720 ml.

The PAWEI may additionally be displayed breath by breath on an enlarged scale to identify increasing or decreasing EL at the end-inspiratory lung-volume level. PEEP is lowered and, after about 2 minutes, the AEELVdown and the mean of AEELVup and AEELVdown is shown and EL 10 538 864 (APEEP/AEELVmean) may be displayed. The ratio of APTP/APAW for baseline PEEP level and for the higher PEEP level may be displayed.

Examples - Decision support and monitoring display The complete lung VL/PTP (or PTP/VL) curve with estimated ZEEP/FRC may be displayed, in which PTPEE is equal to PEEP. Figs. 5A and B are examples graphs of complete estimated lung P/V curves corresponding to pulmonary acute respiratory distress syndrome (ARDS) and extrapulmonary ARDS, respectively. These curves may be generated from a single PEEP increase-decrease cycle or more preferably an extended PEEP cycle in which PEEP is increased in two steps followed by PEEP decrease in two steps. Using an equation for the best fit of the lung P/V curve, decision support is possible.

Example - Pulmonary ARDS The following example corresponds to complete estimated lung P/V curves shown in Figs. 6A and B for pulmonary ARDS. Using the equation for the best fit lung P/V curve (y=0.0x3+0.8x2+34), and the fact that the end-expiratory PTP changes as much as PEEP (PAWEE) is changed, this display provides information that makes decision support readily available. ln this case of pulmonary ARDS, an injurious end-inspiratory PTP level of 27 at PEEP 12 can be identified. The corresponding end- expiratory and end-inspiratory lung volume levels (above FRC) are 525 and 1125 ml. lf oxygenation is inadequate, a suggested increase in PEEP level to 15 cmHzO with an increase in EELV from 525 to 690 ml, to improve oxygenation can be combined with a reduction of tidal volume from 600 to 350 ml, resulting in an end-inspiratory lung volume to 1040 ml and a lowered end-inspiratory PTP to 24 cmHzO, slightly below the upper inflection point.

Example - Extrapulmonary ARDS The following example corresponds to complete estimated lung P/V curves shown in Figs. 7A and B for pulmonary ARDS. Using the equation for the best fit lung P/V curve (y=-0.0x3+2.5x2+36) and the fact that the end-expiratory PTP changes as much as PEEP (PAWEE) is changed, this display provides information that makes decision support readily available. ln this case of extrapulmonary ARDS, the PTPEI level of 18 cmHzO at PEEP 12 can be identified. The corresponding end-expiratory and end- inspiratory lung volume levels (above FRC) are 400 and 975 ml. lf oxygenation is inadequate, a suggested increase of PEEP level to 16 cmHzO with an increase in EELV from 400 to 775 ml can be combined with a reduction of tidal volume from 575 to 425 ml, resulting in an end-inspiratory lung volume to 1200 ml and an end-inspiratory PTP only 1.5 cmHzO higher than before, i.e. 19.5 cmHzO and, well below a possible risk level (pre-determined maximum PTP) of 24 cmH20. The pre- 11 538 864 determined maximum PTP may be higher or lower than 24 cmHzO as determined by a user (e.g. a clinician or respiratory therapist).

Example - measurement sequence and complete lung P/V calculation procedure Increase PEEP from baseline clinical value and determine the increase in EELV, AEELVup.

Decrease PEEP to baseline level and determine the decrease in EELV, AEELVdown.

Calculate the mean AEELVup and down, AEELVmean.

Set tídal volume equal to AEELVmean.

Determine respiratory system elastance, EToT as PAWE|p|ateau/VT=AEELVmean.

Determine lung elastance, EL, as APEEP/AEELVmean.

Determine chest wall elastance, ECW as ETOT - EL.

Determine PTPE| at baseline PEEP as baseline PAWHBL- ECW x VT.

Determine PTPEI at increased PEEP as PAWEI Hm - ECW x VT.

Plot PEEPBL, PEEPHP1, PTPEIBL and PTPHPI versus corresponding lung volume.

Determine the best fit curve equation (polynomial, second and/or third degree) of PTP/V points.

Use the equation for decision support.

The systems and methods described herein may be embodied by a computer program or a plurality of computer programs, which may exist in a variety of forms both active and inactive in a single computer system or across multiple computer systems. For example, they may exist as software program(s) comprised of program instructions in source code, object code, executable code, or other formats for performing some of the method steps. Any of the above may be embodied on a computer readable medium, which includes storage devices and signals in compressed or uncompressed form. The term ”computer” refers to any electronic device comprising a processor, such as a general-purpose central processing unit (CPU), a specific purpose processor, or a microcontroller. A computer is capable of receiving data (an input), performing a sequence of predetermined operations on received data, and producing a result in the form of information or signals (an output) resulting from the predetermined operations. 12

Claims (10)

538 864 Claims

1. A system including a breathing apparatus and a processing unit configured to: raise a first positive end-expiratory pressure PEEP level to at least a second PEEP level above said first PEEP level, determine an increase in end expiratory lung volume EELV (AEELVup) and subsequently lowering said second PEEP level to said first PEEP level, determine a decrease in EELV (AEELVdown), calculate a change in end-expiratory lung volume (AEELVmean) between said first PEEP level and said second PEEP level as (AEELVup/AEELVdown)/2, set a tidal volume to be equal to AEELVmean, and calculate a lung mechanics and chest wall mechanics equation related to the lung volume between the end-expiratory lung volume at the first PEEP level and the end-expiratory lung volume at the second PEEP level to transpulmonary pressure (PTP) of a lung connected to said breathing apparatus, at said tidal volume equal to AEELVmean.

2. The system of claim 1, wherein said processing unit is further configured to calculate any one of end-inspiratory transpulmonary pressure (PTPEI), tidal volume (VT) and PEEP from any two of the other of PTPEI, VT and PEEP using said lung mechanics equation.

3. The system of claim 1 or claim 2, and further comprising a display unit operatively connected to said processing unit, said processing unit being configured to provide on said display unit a graphical visualization of said lung mechanics equation.

4. The system of claim 3, wherein said graphical visualization is a complete lung P/V curve generated using one or more step changes in PEEP level.

5. The system of claim 3, further comprising a graphical visualization including information relating breath-by-breath changes in lung volume in response to a change in PEEP level.

6. The system of any one of claims 1 - 5, further comprising a graphical user interface, said graphical user interface including a graphical visualization including a combination of values for PTPEI, VT and PEEP, wherein at least of said of PTPEI, VT and PEEP values is calculated based on said lung mechanics equation.

7. A method of setting a desired value of a ventilation parameter in a breathing apparatus connected to a test lung, model lung or artificial lung, said method comprising: calculating a value for PTPEI using said lung mechanics equation calculated by the system of claim 2 and selecting a VT and PEEP based upon said lung mechanics equation.

8. A method of adjusting at least one second ventilation parameter in a breathing apparatus for a ventilation of a connected test lung, model lung or artificial lung based on a target input of a first ventilation parameter from a clinical user, said method including: 13 538 864 raising a first positive end-expiratory pressure PEEP level to at least a second PEEP level above said first PEEP level, determining an increase in end expiratory lung volume EELV (AEELVup) and subsequently lowering said second PEEP level to said first PEEP level, determining a decrease in EELV (AEELVdown), calculating a change in end-expiratory lung volume (AEELVmean) between said first PEEP level and said second PEEP level as (AEELVup/AEELVdown)/2, setting a tidal volume to be equal to AEELVmean, and calculating a lung mechanics and chest wall mechanics equation related to the lung volume between the end-expiratory lung volume at the first PEEP level and the end-expiratory lung volume at the second PEEP level to transpulmonary pressure (PTP) of the test lung, model lung or artificial lung connected to said breathing apparatus, at said AEELVmean, and adjusting the at least one second ventilation parameter, the at least one second ventilation parameter being at least one of PTPEI, VT and PEEP based on said lung mechanics equation.

9. The method of claim 8 and further comprising calculating breath-by-breath change in EELV in response to a change in PEEP level from a first PEEP level to a second PEEP level and therefrom determining whether the lung exhibit increased, decreased, or constant elastance between said first and second PEEP levels.

10. A computer program, preferably embodied on a computer-readable medium, for performing the method of any of claims 7-9. 14