Automatic PEEP selection for mechanical ventilation

The present disclosure pertains to a system (10) configured to automatically set the positive end expiratory pressure (PEEP) during mechanical ventilation (800). The system uses a measured relationship between transpulmonary pressure and lung volume (804) to set PEEP (808) such that mechanically assisted breaths are delivered more effectively to open airways (e.g., tidal breaths will be delivered to airways that consist of alveoli that have not contracted or collapsed at the end of expiration) (810). Furthermore, the system is configured to sense (18, 804) when the lungs may be either hyperextended and/or undergoing cyclic atelectasis in order to prevent trauma or injury to the lung's fibrous tissue. The system is configured to perform recruitment and/or continuous monitoring and adjustment of the PEEP setting to maintain an open lung.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure pertains to a method and a mechanical ventilator system for and controlling positive end expiratory pressure (PEEP) for a subject.

2. Description of the Related Art

A mechanical ventilator assists breathing by pushing air into a patient's lungs. Ventilators may operate under different control modes. Methods to dynamically and automatically combine recruitment maneuvers with the proper selection and maintenance of PEEP require static observations of lung volume with applied pressure. These methods are cumbersome and do not assess alveolar recruitment in real time, therefore requiring continual observation of the patient to prevent over distention, atelectasis or cyclic shearing of the alveoli.

SUMMARY OF THE INVENTION

Accordingly, one or more aspects of the present disclosure relate to a mechanical ventilator system configured to control positive end expiratory pressure (PEEP) in a subject. The mechanical ventilator system comprises a pressure generator, one or more sensors, one or more hardware processors, and/or other components. The pressure generator is configured to generate a pressurized flow of breathable gas for delivery to an airway of the subject. The one or more sensors are configured to generate output signals conveying information related to breathing of the subject. The one or more hardware processors are operatively coupled to the pressure generator and the one or more sensors and configured by machine-readable instructions to: determine tidal volume and transpulmonary pressure of the subject based on the information in the output signals; determine lung volume based on the tidal volume; determine a target PEEP level based on the lung volume and the transpulmonary pressure; and cause the pressure generator to adjust the pressurized flow of breathable gas to maintain the determined target PEEP level.

Another aspect of the present disclosure relates to a method for controlling PEEP in a subject with a mechanical ventilator system. The mechanical ventilator system comprises a pressure generator, one or more sensors, one or more hardware processors, and/or other components. The method comprises: generating, with the pressure generator, a pressurized flow of breathable gas for delivery to an airway of the subject; generating, with the one or more sensors, output signals conveying information related to breathing of the subject; determining, with the one or more hardware processors, tidal volume and transpulmonary pressure of the subject based on the information in the output signals; determining, with the one or more hardware processors, lung volume based on the tidal volume; determining, with the one or more hardware processors, a target PEEP level based on the lung volume and the transpulmonary pressure; and causing, with the one or more hardware processors, the pressure generator to adjust the pressurized flow of breathable gas to maintain the determined target PEEP level.

Still another aspect of the present disclosure relates to a system for controlling PEEP in a subject. The system comprises: means for generating a pressurized flow of breathable gas for delivery to an airway of the subject; means for generating output signals conveying information related to breathing of the subject; means for determining tidal volume and transpulmonary pressure of the subject based on the information in the output signals; means for determining, with the one or more hardware processors, lung volume based on the tidal volume; means for determining a target PEEP level based on the lung volume and the transpulmonary pressure; and means for causing the means for generating the pressurized flow of breathable gas to adjust the pressurized flow of breathable gas to maintain the determined target PEEP level.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1is a schematic illustration of a mechanical ventilator system10configured to control positive end expiratory pressure (PEEP) in a subject12. In some embodiments, controlling PEEP includes selecting and maintaining target PEEP levels in subject12. Collapsed lungs require applied pressure to expand alveoli. Once an alveolus is open, the alveolus tends to interact with neighboring alveoli and remain open. Recruitment maneuvers are used to open collapsed lungs and improve mechanical ventilation in subjects with respiratory difficulties. PEEP is controlled during recruitment maneuvers and/or at other times to prevent cyclic collapse as part of an open lung approach to ventilation in order to increase end-expiratory lung volume, improve gas exchange, decrease ventilator-induced lung injury (VILI), and/or for other reasons. Recruitment maneuvers include a temporary increase in airway pressure configured to open up collapsed alveoli. De-recruitment can occur, for instance, due to poor ventilation, insufficient PEEP, and/or chest wall instability, for example. Collapsed alveoli may lead to poor gas exchange and increased risk of VILI. Some alveoli may collapse during a breath, cyclically collapse and re-expand with individual breaths, and/or collapse at other times. At the same time, other alveoli in the lungs may remain inflated and/or become over inflated by high tidal volumes and pressures, causing volutrauma. Recruitment maneuvers may be used in subjects with severe acute respiratory distress syndrome (ARDS) and/or other subjects, may be a component of a lung protective ventilation strategy, and/or they may be used as part of an open lung approach to mechanical ventilation for example.

System10is configured to dynamically and automatically select and maintain a target PEEP level for and/or during recruitment maneuvers. Prior methods require static observations of subject lung volume and applied pressure. These prior methods are cumbersome and do not continue to assess alveolar recruitment in real time, therefore requiring continual observation of a subject to prevent over distention, atelectasis or cyclic shearing of the alveoli. As a subject in acute respiratory distress evolves, periodic recruitment maneuvers are occasionally needed to maintain an open lung. The target PEEP level needed during these maneuvers may vary over time (e.g., caused by surfactant treatment, the natural production of the lipids contained in surfactant to decrease the surface tension in the alveoli, and/or other factors). The varying need to assess and adjust a target PEEP level is a heavy burden on any caregiver during the administration of mechanical ventilation.

Existing tools available to caregivers to maintain an open lung are inadequate. For example, the pressure/volume (p-v) loops produced by typical ventilator systems plot tidal volume against mouth pressure. Such loops confound information pertaining to the alveoli by not taking into account the resistive pressure drop across the airways of a subject and subject (e.g., muscular) effort that contributes to the transmural pressure impacting the alveoli. As a consequence, the p-v loops need to be interpreted by a caregiver and, typically, static maneuvers by the caregiver (e.g., manually increasing pressure and observing the resulting tidal volume) are necessary to characterize the p-v relationship of the lung itself. Manually performed recruitment maneuvers require the presence of skilled personnel. As a consequence, such maneuvers are performed infrequently. The lack of continuous monitoring of PEEP further exacerbates the problem of infrequent recruitment maneuvers.

Advantageously, system10is configured to determine a target PEEP level based on a p-v curve with lung volume plotted against the transpulmonary pressure (i.e., the difference in pressure across the elastic compartment of the respiratory system (lung and chest wall)). Performing a recruitment maneuver typically involves high pressures in the lungs. System10is configured to monitor the alveolar (and, in turn, transpulmonary) pressure, rather than mouth pressure, and ensure it is maintained within safe limits.

System10is configured to determine the p-v curve (lung volume vs. transpulmonary pressure) in real-time and/or near real-time to facilitate automatic lung recruitment with a target PEEP level set and maintained throughout mechanical ventilation. System10is configured to help caregivers in their daily management of subjects by eliminating the need for performing manual recruitment maneuvers, among other advantages. System10is also useful during, for example, catastrophic events where a large number of people may need ventilation in the absence of skilled caregivers.

In some embodiments, system10comprises one or more of a pressure generator14, a subject interface16, one or more sensors18, one or more processors20, a user interface22, electronic storage24, and/or other components.

Pressure generator14is configured to generate a pressurized flow of breathable gas for delivery to the airway of subject12. Pressure generator14may control one or more ventilation parameters of the flow of gas (e.g., rates, pressures, volumes, temperatures, compositions, etc.) for therapeutic purposes, and/or for other purposes. Pressure generator14is configured to control one or more ventilation parameters of the pressurized flow of breathable gas according to a prescribed mechanical ventilation therapy regime and/or other therapy regimes. By way of a non-limiting example, pressure generator14may be configured to control a breath rate, a flow rate, a mouth pressure waveform, a positive end expiratory pressure (PEEP), a tidal volume, a minute volume, an inspiratory to expiratory breath phase ratio (e.g., an I:E ratio), and/or other ventilation parameters of the flow of gas.

Pressure generator14receives a flow of gas from a gas source, such as the ambient atmosphere, and elevates and/or reduces the pressure of that gas for delivery to the airway of subject12. Pressure generator14is and/or includes any device, such as, for example, a pump, blower, piston, or bellows, that is capable of elevating and/or reducing the pressure of the received gas for delivery to a patient. Pressure generator14may comprise servo controlled valves and/or motors, one or more other valves and/or motors for controlling the pressure and/or flow of gas, and/or other components. The present disclosure also contemplates controlling the operating speed of the blower, either alone or in combination with such valves, to control the pressure and/or flow of gas provided to subject12.

Subject interface16is configured to deliver the pressurized flow of breathable gas to the airway of subject12. As such, subject interface16comprises conduit30, interface appliance32, and/or other components. Conduit30is configured to convey the pressurized flow of gas to interface appliance32. Conduit30may be a flexible length of hose, or other conduit that places interface appliance32in fluid communication with pressure generator14. Interface appliance32is configured to deliver the flow of gas to the airway of subject12. In some embodiments, interface appliance32is non-invasive. As such, interface appliance32non-invasively engages subject12. Non-invasive engagement comprises removably engaging an area (or areas) surrounding one or more external orifices of the airway of subject12(e.g., nostrils and/or mouth) to communicate gas between the airway of subject12and interface appliance32. Some examples of non-invasive interface appliance32may comprise, for example, a nasal cannula, a nasal mask, a nasal/oral mask, a full face mask, a total face mask, or other interface appliances that communicate a flow of gas with an airway of a subject. The present disclosure is not limited to these examples, and contemplates delivery of the flow of gas to the subject using any interface appliance, including an invasive interface appliance such as an endotracheal tube and/or other appliances.

Sensors18are configured to generate output signals conveying information related to breathing of subject12and/or other gas and/or breathing parameters. In some embodiments, the information related to breathing of subject12includes the flow rate (and/or information related to the flow rate) of the pressurized flow of breathable gas, pressure of the pressurized flow of breathable gas at the mouth of subject12and/or other locations, and/or other information. In some embodiments, the information related to breathing of subject12may comprise information related to volumes (e.g., tidal volume, minute volume, etc.), pressures (e.g., inhalation pressure, exhalation pressure, etc.), compositions (e.g., concentration(s)) of one or more constituent gasses, a gas temperature, a gas humidity, acceleration, velocity, acoustics, changes in a parameter indicative of respiratory effort by subject12, and/or other parameters. In some embodiments, sensors18may generate output signals substantially continuously, at predetermined intervals, responsive to occurrence of a predetermined event, and/or at other times. In some embodiments, the predetermined intervals, events, and/or other information may be determined at manufacture, based on user input via user interface22, and/or based on other information.

Sensors18may comprise one or more sensors that measure such parameters directly (e.g., through fluid communication with the flow of gas in subject interface16). Sensors18may comprise one or more sensors that generate output signals related to one or more parameters of the flow of gas indirectly. For example, one or more of sensors18may generate an output based on an operating parameter of pressure generator14(e.g., a valve driver or motor current, voltage, rotational velocity, and/or other operating parameters).

Although sensors18are illustrated at a single location within (or in communication with) conduit30between interface appliance32and pressure generator14, this is not intended to be limiting. Sensors18may include sensors disposed in a plurality of locations, such as for example, within pressure generator14, within (or in communication with) interface appliance32, in communication with subject12, and/or in other locations. For example, sensors18may include a flow rate sensor, a pressure sensor conveying information related a pressure of breathable gas at the mouth of subject12and/or other locations, a volume sensor, a temperature sensor, an acoustic sensor, a gas composition (e.g., an SpO2sensor) sensor, and/or other sensors located at various locations in system10.

Processor20is configured to provide information processing capabilities in system10. As such, processor20may comprise one or more of a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information. Although processor20is shown inFIG. 1as a single entity, this is for illustrative purposes only. In some implementations, processor20may comprise a plurality of processing units. These processing units may be physically located within the same device (e.g., pressure generator14), or processor20may represent processing functionality of a plurality of devices operating in coordination.

As shown inFIG. 1, processor20is configured to execute one or more computer program components. The one or more computer program components may comprise one or more of a parameter component40, a PEEP component42, a control component44, and/or other components. Processor20may be configured to execute components40,42, and/or44by software; hardware; firmware; some combination of software, hardware, and/or firmware; and/or other mechanisms for configuring processing capabilities on processor20. In some embodiments, processor20may execute one or more of the operations described below and/or other operations substantially continuously (e.g., in real-time and/or near real-time), at predetermined intervals, responsive to occurrence of a predetermined event, and/or at other times. In some embodiments, the predetermined intervals, events, and/or other information may be determined at manufacture, based on user input via user interface22, and/or based on other information.

It should be appreciated that although components40,42, and44are illustrated inFIG. 1as being co-located within a single processing unit, in implementations in which processor20comprises multiple processing units, one or more of components40,42, and/or44may be located remotely from the other components. The description of the functionality provided by the different components40,42, and/or44described below is for illustrative purposes, and is not intended to be limiting, as any of components40,42, and/or44may provide more or less functionality than is described. For example, one or more of components40,42, and/or44may be eliminated, and some or all of its functionality may be provided by other components40,42, and/or44. As another example, processor20may be configured to execute one or more additional components that may perform some or all of the functionality attributed below to one of components40,42, and/or44.

Parameter component40is configured to determine tidal volume, lung volume, transpulmonary pressure, PEEP, and/or other parameters related to the pressurized flow of breathable gas and/or the breathing of subject12. In some embodiments, the tidal volume, lung volume, the transpulmonary pressure, PEEP, and/or other parameters are determined based on the information in the output signals, determinations of one or more other parameters, and/or other information. For example, lung volume may be determined based on tidal volume by stitching together several measurements of tidal volume. In some embodiments, the information related to the breathing of subject12(e.g., the information in the output signals) includes a flow rate of the pressurized flow of breathable gas (Q), a pressure of breathable gas at a mouth of the subject (Pao), and/or other information. In some embodiments, determining the tidal volume for subject12based on the information in the output signals comprises multiplying the flow rate by a period of time that corresponds to a given breath. In some embodiments, determining the transpulmonary pressure of subject12based on the information in the output signals comprises determining an airway resistance (R) and elasticity (E) based on Q and Pao, determining alveolar pressure (Pal) and muscular pressure (Pmus) in subject12based on R and E, and determining the transpulmonary pressure based on Paland Pmus.

FIG. 2schematically illustrates how the above parameters are dynamically related to each other. The patient's respiratory system is modeled as a single compartment, represented inFIG. 2as an electrical analogue200. The lungs and chest wall are modeled as an elastic compartment served by a single resistive pathway (airways). The pressure at the entrance of the resistive pathway corresponds to the airway opening pressure (Pao202), whereas the pressure inside the elastic compartment is representative of the alveolar pressure (Pal208). The system is subject to an external pressure (Pmus212) that represents an equivalent pressure of the force exerted by the respiratory muscles. The dynamics of the airflow Q through the different components of the respiratory system is driven by the pressure difference Pao-Pmus. The elastic properties of the elastic compartment are described by the elastance parameter E210and the resistive properties of the resistive component are described by the resistance parameter R204.

Using the model shown inFIG. 2, the transpulmonary pressure, or the pressure across the elastic compartment of the respiratory system, can be determined by subtracting Pmusfrom Pal, where the elastic element E210includes both the lungs and the chest wall. Determining a resistance (R) and elasticity (E) based on Q and Pao(e.g., determined based on the information in the output signals from sensors18) may be performed according to the equation(s) shown below and/or other equations. For example:
τ=median(−(V(t)−V(t0))/(Q(t)−Q(t0))),
over the time samples t during exhalation at which the ventilator is providing the set PEEP. Also:
E=(Pao(tEOI)−Pao(t0))/(τ(Q(tEOI)−Q(t0))+(V(tEOI)−V(t0))); and
R=τE,
where t0is the time at which the patient initiates the breath (or the ventilator does, if the patient is passive) and tEOIis the time at which the ventilator cycles off. τ is the respiratory system time constant, which can be estimated as a median (like above) or, for instance, by the ordinary least-squares method. Determining alveolar pressure (Pal) and muscular pressure (Pmus) in subject12based on R and E may be performed according to the equation(s) shown below and/or other equations. For example:
Pal(t)=Pao(t)−RQ(t); and
Pmus(t)=Pao(t)−RQ(t)−E(V(t)−(V(t0))−Pal(t0).

As described above, determining the transpulmonary pressure Ptranspulmonarybased on Paland Pmusmay be performed according to the equation shown below and/or other equations.
Ptranspulmonary(t)=Pal(t)−Pmus(t)

By way of a non-limiting example,FIG. 3is an input-output diagram300showing determination302(e.g., using the equations described above) of parameters R204, Pal208, E210, and Pmus212based on Pao202and Q206. As shown inFIG. 3, system10(FIG. 1) is configured such that only air flow (Q206) and pressure (Pao202) measurements made based on information in output signals from sensors18located in communication with subject interface16at the mouth of subject12are needed to make breath by breath estimates of R204, E210, Pat208, Pmus212, and/or other parameters. In some embodiments (e.g., during non-invasive ventilation), flow and pressure at the mouth of the subject are estimated based on flow and pressure measurements obtained with sensors located in the ventilator.

In some embodiments, transmural pressure (Pat—pleural pressure (Ppl)) is determined instead of and/or in addition to transpulmonary pressure, and the target PEEP level is determined (e.g., as described herein) based on the lung volume, the transmural pressure, and/or other information. In such embodiments, subject interface16(FIG. 1) and/or sensors18(FIG. 1) may include one or more invasive components configured to facilitate measurement of pleural pressure (e.g., via an esophageal catheter and/or other components).

Returning toFIG. 1, PEEP component42is configured to determine a target PEEP level. The target PEEP level is determined based on the information in the output signals from sensors18, the parameters determined by parameter component40(e.g., including the lung volume, the transpulmonary pressure, and/or other parameters), and/or other information. In some embodiments, PEEP component42is configured to determine a target PEEP level by controlling pressure generator14to generate the pressurized flow of breathable gas to achieve a series of increasing PEEP levels in subject12over a series of breaths by subject12and determining airway compliance C (e.g., I/E described above) for the individual PEEP levels. In some embodiments, PEEP component42is configured such that the breaths with increasing PEEP levels are tidal volume controlled and/or alveolar pressure limited during breathing to ensure safety of subject12(e.g., wherein the necessary safety determinations are made based on the information in the output signals from sensors18, based on limitations and/or other entries and/or selections made via user interface22, and/or based on other information). A tidal volume controlled and alveolar pressure limited breath is a breath delivered with pressure support or ramping pressure until the inhaled volume reaches the volume threshold given by a prescription, for example.

FIG. 4illustrates airway compliance C400as a function if increasing PEEP401levels402,404,406, and408. In such embodiments, based on the compliance versus PEEP information (e.g., the information inFIG. 4), PEEP component42(FIG. 1) is configured to set the target PEEP level at or near PEEP levels that generate maximum or near-maximum lung compliance in subject12(FIG. 1). UsingFIG. 4as an example, maximum lung compliance (or minimum elastance)410is achieved at or near PEEP levels404and406so PEEP component42would set the target PEEP level412to a level at or near PEEP levels404and/or406.

In some embodiments, determining the target PEEP level based on the lung volume and the transpulmonary pressure comprises determining a lung volume (e.g., by stitching together several measurements of tidal volume) versus transpulmonary pressure (e.g., determined as described above) curve based on the information in the output signals, parameters determined by parameter component40(FIG. 1), and/or other information. In some embodiments, the lung volume portion of the curve is generated by stitching together many measurements of tidal volume and offsetting them by the start volume at the beginning of the breath, and/or by other methods.FIG. 5illustrates an example of a lung volume (V)500versus transpulmonary pressure (Ptranspulmonary)502curve504for subject12(FIG. 1). In some embodiments, PEEP component42(FIG. 1) is configured to determine curve504by controlling pressure generator14(FIG. 1) to generate the pressurized flow of breathable gas to achieve a series of increasing PEEP levels506,508,510, and512in subject12over a series of breaths514,516,518, and520by subject12and plotting the resulting lung volume versus transpulmonary pressure (e.g., determined as described above) for the individual breaths514-520. As shown inFIG. 5, information generated for the individual breaths514-520is used to determine corresponding portions522-528of curve504.

A transpulmonary pressure p-v curve of the lungs of subject12(FIG. 1) features three main regions. At low pressure, the curve is generally flat (e.g., large changes in pressure are needed to achieve relatively small changes in volume). This corresponds to low lung compliance. A central region of the curve is characterized by higher lung compliance and corresponds to a pressure range within which the lungs operate at their best, without alveolar collapse or overstretching. At higher pressures, the p-v curve becomes flat as again large changes in pressure are needed to achieve relatively small changes in volume.

FIG. 6illustrates another example p (transpulmonary)-v (lung) curve600of the lungs of subject12(e.g., for simplicity hysteresis and/or interaction of the alveoli to maintain themselves once opened is not shown inFIG. 6).FIG. 6illustrates a lower region602where, at low pressure, curve600is generally flat (e.g., large changes in pressure are needed to achieve relatively small changes in volume).FIG. 6illustrates a central region604of curve600characterized by higher lung compliance, and a higher region606where, at higher pressures, p-v curve600becomes flat as again large changes in transpulmonary pressure are needed to achieve relatively small changes in volume. As shown inFIG. 6, region602transitions to region604at a concave up inflection point608in curve600, and region604transitions to region606at a concave down inflection point610in curve600. Also inFIG. 6, the Ptranspulmonaryaxis shows the pressure across the elastic compartment of the respiratory system (e.g., Pal-Pmus, where the elastic element includes both the lungs and the chest wall).

Returning toFIG. 1, in some embodiments, PEEP component42is configured such that determining the target PEEP level based on the lung volume and the transpulmonary pressure comprises identifying one or more inflection points (e.g.,608and/or610shown inFIG. 6) in the p (transpulmonary)-v (lung) curve, determining the target PEEP level based on the one or more inflection points, and/or performing other operations. In some embodiments, PEEP component42determines inflection points in the p (transpulmonary)-v (lung) curve by, for instance, detecting changes in the value of the derivative of curve600. In some embodiments, PEEP component42is configured such that the derivative can be computed locally (i.e., point by point, along curve600) using a Savitzky-Golay smoothening filter, and/or other techniques.

In some embodiments, determining the target PEEP level based on the lung volume and the transpulmonary pressure further comprises identifying a concave up inflection point in the curve and/or causing pressure generator14to adjust the pressurized flow of breathable gas to increase therapy PEEP levels in subject12for individual breaths in a series of subsequent breaths until a concave up inflection point is no longer identified in a portion of the curve that corresponds to a most recent breath. In some embodiments, determining the target PEEP level based on the lung volume and the transpulmonary pressure further comprises identifying a concave down inflection point in the curve, causing pressure generator14to adjust the pressurized flow of breathable gas to decrease therapy PEEP levels in subject12for individual breaths in a series of subsequent breaths until a concave up inflection point is identified, causing pressure generator14to adjust the pressurized flow of breathable gas to increase therapy PEEP levels for at least one further breath to a level between the concave down inflection point and the concave up inflection point, and setting the target PEEP level to a level between a pressure that corresponds to the concave up inflection point and the therapy PEEP level for the at least one further breath to maintain an open airway in subject12.

For example,FIG. 7illustrates one possible set of operations700performed by PEEP component42(FIG. 1) to determine a target PEEP level. As described above, PEEP component42may cause pressure generator14(FIG. 1) to generate the pressurized flow of breathable gas to achieve a series of PEEP levels (e.g., PEEP1-PEEP7) in subject12(FIG. 1) over a series of breaths (e.g.,1-7) by subject12.FIG. 7illustrates identifying a concave down inflection point in the curve702, causing pressure generator14to adjust the pressurized flow of breathable gas to decrease therapy PEEP levels (e.g., PEEP2-PEEP5) in subject12for individual breaths (e.g., breaths2-5) in a series of subsequent breaths until a concave up inflection point704is identified, causing pressure generator14to adjust the pressurized flow of breathable gas to increase therapy PEEP levels (e.g., PEEP6) for at least one further breath (e.g., breath6) to a level between concave down inflection point702and concave up inflection point704, closer to702, and eventually setting the target PEEP level to a level (e.g., PEEP7) between concave down inflection point702and concave up inflection point704, closer to704, to maintain an open airway in subject12.

Returning toFIG. 1, in some embodiments, PEEP component42is configured to perform one or more of the operations described above to determine a target PEEP level one or more times per breath of subject12such that target PEEP levels are determined in real-time and/or near real-time (e.g., such that a plot like the plot illustrated inFIG. 6may be generated and/or updated for individual breaths of subject12). In some embodiments, PEEP component42is configured to perform one or more of the operations described above responsive to detection of a concave up inflection point in a p (transpulmonary)-v (lung) curve. In some embodiments, PEEP component42is configured to perform one or more of the operations described above responsive to one or more parameters determined by parameter component40breaching a threshold level. For example, PEEP component42may be configured to perform one or more of the operations described above to determine a target PEEP level responsive to parameters indicating a low ventilation alarm condition (e.g., one or more parameters breaching a low ventilation alarm threshold), a SpO2 level breaching an SpO2 alarm threshold level, and/or responsive to other parameters breaching other thresholds. In some embodiments, PEEP component42is configured to perform one or more of the operations described above to determine a target PEEP level at predetermined intervals that may or may not correspond to the breathing of subject12. In some embodiments, PEEP component42is configured to perform one or more of the operations described above to determine a target PEEP level responsive to manual instructions received from a user (e.g., via user entry and/or selection of such instructions via user interface22and/or other components of system10). In some embodiments, the timing of the target PEEP level determinations (e.g., real-time, near real-time, responsive to threshold breach, at predetermined intervals, responsive to manual instructions, etc.) is set at manufacture, determined and/or adjusted based on user input via user interface22, and/or determined by other methods.

Control component44is configured to control pressure generator14to generate the pressurized flow of breathable gas. The pressurized flow of gas generated by pressure generator14is controlled to replace and/or compliment the regular breathing of subject12. In some embodiments, control component44is configured to cause pressure generator14to generate the pressurized flow of breathable gas in accordance with a prescribed mechanical ventilation therapy regime. In such embodiments, control component44is configured to cause pressure generator14to control the one or more ventilation parameters of the pressurized flow of breathable gas (e.g., as described above) according to the prescribed mechanical ventilation therapy regime. In some embodiments, control component44may be configured to control pressure generator14to generate the flow of gas in accordance with a ventilation and/or positive airway pressure support therapy regime in addition to and/or instead of a mechanical ventilation therapy regime. By way of non-limiting example, control component44may control pressure generator14such that the pressure support provided to subject12via the flow of gas comprises continuous positive airway pressure support (variable CPAP), variable bi-level positive airway pressure support (BPAP), proportional positive airway pressure support (PPAP), and/or other types of pressure support therapy.

In some embodiments, control component44is configured to cause pressure generator14to adjust the pressurized flow of breathable gas to provide the therapy PEEP levels describe herein (e.g., the adjusted PEEP levels described above used to determine target PEEP levels) and/or maintain a determined target PEEP level. Maintaining the determined target PEEP level may facilitate maintenance of an open airway in subject12so that oxygen and carbon dioxide may be exchanged more easily, requiring little and/or no effort from subject12in order to facilitate gas exchange. Control component44is configured to control pressure generator14based on information related to the output signals from sensors18, information determined by PEEP component42and/or parameter component40, information entered and/or selected by a user via user interface22, and/or other information.

By way of a non-limiting practical example of the operation of components40,42, and/or44of processor20and/or other components of system10described herein, system10may deliver a recruitment maneuver (e.g., autonomously triggered by system10and/or manually triggered by an external user) comprising a series of increasing tidal volume controlled and alveolar pressure limited breaths (pressures) to subject12, beginning at an initial PEEP of 15 cmH2O, for example. As described above, tidal volume controlled and alveolar pressure limited breaths are breaths delivered with pressure support and/or ramping pressure until the inhaled volume reaches the volume threshold given by a prescription (e.g., 6 cc/kg ideal body weight (IBW) entered and/or selected via user interface22and/or other components of system10) and/or until the alveolar pressure reaches 30 cmH2O, as an example, after which the pressure is lowered back to the PEEP setting. System10may cause delivery one or more of these breaths in order to stabilize the parameter estimation algorithms described above, and/or build a robust estimate of a corresponding p (transpulmonary)-v (lung) curve segment (e.g., by averaging determinations from different breaths). If an inflection point with upward concavity is detected in the estimated p-v curve segment, then PEEP may be increased to a level of pressure corresponding to the inflection point plus 2 cmH2O, for example. Further breaths may then be delivered at the new PEEP level while further breathing parameters continue to be determined and the above procedure is repeated until the determined segment of the p-v curve does not feature the lower inflection point (the concave up inflection point).

If a detected inflection point is concave down, then system10is configured such that the PEEP level setting is decreased by as many cmH2O as needed to move down the p-v curve and make the upper inflection point (the concave down inflection point) disappear for a given curve segment (e.g., segments524and526inFIG. 5). Afterwards, successive decreases in PEEP levels are made (while breaths are continually delivered) until the concave up inflection point appears. This level of PEEP corresponds to atelectasis and system10sets the target PEEP level above this pressure. The recruitment procedure (stepped increases in the PEEP level) is repeated, but is subsequently followed with a decrease in PEEP to a level 2 cm H2O, for example, above the learned level of PEEP that caused atelectasis. It should be noted that atelectasis may be detected at any time by system10during the administration of mechanical ventilation via detection of the lower inflection point (the concave up inflection point). As described above, responsive to detection of a concave up inflection point by system10(e.g., PEEP component42) and/or other events, system10(e.g., PEEP component42and/or pressure generator14) is configured to perform a recruitment maneuver according to the procedure described herein.

User interface22is configured to provide an interface between system10and subject12and/or other users through which subject12and/or other users provide information to and receive information from system10. Other users may comprise a caregiver, a doctor, a family member, a decision maker, and/or other users. User interface22enables data, cues, results, and/or instructions and any other communicable items, collectively referred to as “information,” to be communicated between a user (e.g., subject12) and one or more of pressure generator14, sensors18, processor20, electronic storage24, and/or other components of system10. Examples of interface devices suitable for inclusion in user interface22comprise a keypad, buttons, switches, a keyboard, knobs, levers, a display screen, a touch screen, speakers, a microphone, an indicator light, an audible alarm, a printer, a tactile feedback device, and/or other interface devices. In some embodiments, user interface22comprises a plurality of separate interfaces. In some embodiments, user interface22comprises at least one interface that is provided integrally with pressure generator14.

It is to be understood that other communication techniques, either hard-wired or wireless, are also contemplated by the present disclosure as user interface22. For example, the present disclosure contemplates that user interface22may be integrated with a removable storage interface provided by electronic storage24. In this example, information may be loaded into system10from removable storage (e.g., a smart card, a flash drive, a removable disk, etc.) that enables the user(s) to customize the implementation of system10. Other exemplary input devices and techniques adapted for use with system10as user interface22comprise, but are not limited to, an RS-232 port, RF link, an IR link, modem (telephone, cable or other). In short, any technique for communicating information with system10is contemplated by the present disclosure as user interface22.

In some embodiments, electronic storage24comprises electronic storage media that electronically stores information. The electronic storage media of electronic storage24may comprise one or both of system storage that is provided integrally (i.e., substantially non-removable) with system10and/or removable storage that is removably connectable to system10via, for example, a port (e.g., a USB port, a firewire port, etc.) or a drive (e.g., a disk drive, etc.). Electronic storage24may comprise one or more of optically readable storage media (e.g., optical disks, etc.), magnetically readable storage media (e.g., magnetic tape, magnetic hard drive, floppy drive, etc.), electrical charge-based storage media (e.g., EPROM, RAM, etc.), solid-state storage media (e.g., flash drive, etc.), and/or other electronically readable storage media. Electronic storage24may store software algorithms, information determined by processor20, information received via user interface22, and/or other information that enables system10to function as described herein. Electronic storage24may be (in whole or in part) a separate component within system10, or electronic storage24may be provided (in whole or in part) integrally with one or more other components of system10(e.g., user interface22, processor20, etc.).

FIG. 8illustrates a method800for controlling PEEP in a subject with a mechanical ventilator system. The mechanical ventilator system comprises a pressure generator, one or more sensors, one or more hardware processors, and/or other components. The one or more hardware processors are configured by machine-readable instructions to execute computer program components. The computer program components include a parameter component, a PEEP component, a control component, and/or other components. The operations of method800presented below are intended to be illustrative. In some embodiments, method800may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of method800are illustrated inFIG. 8and described below is not intended to be limiting.

At an operation802, a pressurized flow of breathable gas is generated for delivery to the airway of the subject. In some embodiments, operation802is performed by a pressure generator the same as or similar to pressure generator14(shown inFIG. 1and described herein).

At an operation804, output signals conveying information related to breathing of the subject are generated. In some embodiments, operation804is performed by one or more sensors the same as or similar to sensors18(shown inFIG. 1and described herein). In some embodiments, the one or more sensors comprise a flow rate sensor configured to generate output signals conveying information related to a flow rate of the pressurized flow of breathable gas, a pressure sensor conveying information related a pressure of breathable gas at a mouth of the subject, and/or other sensors.

At an operation806, lung volume and transpulmonary pressure of the subject are determined. The lung volume and the transpulmonary pressure are determined based on the information in the output signals, based on one or more determined parameters (e.g., the lung volume may be determined based on tidal volume, the tidal volume determined based on the output signals; and the transpulmonary pressure may be determined based on the parameters and equations above), and/or other information. In some embodiments, the information related to the breathing of the subject includes a flow rate of the pressurized flow of breathable gas (Q), a pressure of breathable gas at a mouth of the subject (Pao), and/or other information. In some embodiments, determining the transpulmonary pressure of the subject based on the information in the output signals comprises: determining an airway resistance (R) and elasticity (E) based on Q and Pao; determining alveolar pressure (Pat) and muscular pressure (Pmus) in the subject based on R and E; and determining the transpulmonary pressure based on Paland Pmus. In some embodiments, transmural pressure is determined instead of transpulmonary pressure, and the target PEEP level is determined (e.g., as described herein) based on the lung volume, the transmural pressure, and/or other information. In some embodiments, operation806is performed by a processor component the same as or similar to parameter component40(shown inFIG. 1and described herein).

At an operation808, a target PEEP level is determined. The target PEEP level is determined based on the lung volume, the transpulmonary pressure, and/or other information. In some embodiments, determining the target PEEP level based on the lung volume and the transpulmonary pressure comprises: determining a lung volume versus transpulmonary pressure curve based on the information in the output signals, determined parameters, and/or other information; identifying one or more inflection points in the curve; and determining the target PEEP level based on the one or more inflection points. In some embodiments, determining the target PEEP level based on the lung volume and the transpulmonary pressure further comprises: identifying a concave down inflection point in the curve; causing the pressure generator to adjust the pressurized flow of breathable gas to decrease therapy PEEP levels in the subject for individual breaths in a series of subsequent breaths until a concave up inflection point is identified; causing the pressure generator to adjust the pressurized flow of breathable gas to increase therapy PEEP levels for at least one further breath to a level between the concave down inflection point and the concave up inflection point; and setting the target PEEP level to a level between a pressure that corresponds to the concave up inflection point and the therapy PEEP level for the at least one further breath to maintain an open airway in the subject. In some embodiments, determining the target PEEP level based on the lung volume and the transpulmonary pressure further comprises: identifying a concave up inflection point in the curve; and causing the pressure generator to adjust the pressurized flow of breathable gas to increase therapy PEEP levels in the subject for individual breaths in a series of subsequent breaths until the concave up inflection point is no longer identified in a portion of the curve that corresponds to a most recent breath. In some embodiments, operation808is performed by a processor component the same as or similar to PEEP component42(shown inFIG. 1and described herein).

At an operation810, the pressure generator is caused to adjust the pressurized flow of breathable gas to maintain the determined target PEEP level. In some embodiments, operation810is performed by a processor component the same as or similar to control component44(shown inFIG. 1and described herein).

Although the description provided above provides detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the disclosure is not limited to the expressly disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present disclosure contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.