Method and device for the adaptive regulation of a positive end-expiratory pressure (PEEP)

Abstract

A method controls an expiratory gas flow at a user interface (16) of a ventilator (1) wherein the user interface (16) has an exhalation valve (11), which provides a positive end-expiratory pressure (PEEP). The method includes the following steps during a phase of exhalation: changing the positive end-expiratory pressure from a basic PEEP value (31) with the exhalation valve (11); returning the positive end-expiratory pressure to the basic PEEP value (31) with the exhalation valve (11); and determining an exhalation parameter. The method permits an adaptive change in the expiratory flow during the exhalation. Air trapping can be avoided, and it is possible to respond to changed exhalation parameters within one and the same phase of exhalation.

Claims

1. A method for controlling an expiratory gas flow at a user interface of a ventilator, wherein the user interface has an exhalation valve to provide a positive end-expiratory pressure (PEEP), the method comprising the steps of: during a phase of exhalation, changing, with the exhalation valve, the positive end-expiratory pressure (PEEP) from a basic PEEP value to another PEEP value; during said phase of exhalation, returning, with the exhalation valve, the positive end-expiratory pressure (PEEP) to the basic PEEP; during said phase of exhalation, determining total exhalation resistance values at points in time of said phase of exhalation; providing a plurality of patient exhalation resistance values based on an estimate of partial exhalation resistance of components in an exhalation path of the ventilator and each of the determined total exhalation resistance values; and during said phase of exhalation, determining the expiratory gas flow, wherein the step of changing the positive end-expiratory pressure (PEEP) from the basic PEEP value to another PEEP value comprises reducing the PEEP from the basic PEEP value by a product of the expiratory gas flow times one of the plurality of provided patient exhalation resistance values corresponding in time to the determined expiratory gas flow.

2. A method in accordance with claim 1, further comprising: during said phase of exhalation determining a first intrinsic pressure at the exhalation valve; subsequent to said step of determining the first intrinsic pressure increasing the PEEP from an instantaneous value by means of the exhalation valve at a predefined time during said phase of exhalation; subsequent to said step of increasing the PEEP from the instantaneous value determining a second intrinsic pressure at the exhalation valve; and comparing the first intrinsic pressure and the second intrinsic pressure to determine one or more lung parameters.

3. A method in accordance with claim 2, wherein lung the one or more lung parameters determined by comparing the first intrinsic pressure and the second intrinsic pressure is lung compliance, wherein wherein the determination of the lung compliance comprises calculating a change in gas volume relative to a change in pressure.

4. A control device for controlling an exhalation valve at a user interface of a ventilator, wherein the control device is configured to carry out a method comprising the steps of: during a phase of exhalation, changing, with the exhalation valve, the positive end-expiratory pressure (PEEP) from a basic PEEP value to another PEEP value; during said phase of exhalation, returning, with the exhalation valve, the positive end-expiratory pressure (PEEP) to the basic PEEP; during said phase of exhalation, determining total exhalation resistance values at points in time of said phase of exhalation; providing a plurality of patient exhalation resistance values based on an estimate of partial exhalation resistance of components in an exhalation path of the ventilator and each of the determined total exhalation resistance values; and during said phase of exhalation determining an expiratory gas flow, wherein the step of changing the positive end-expiratory pressure (PEEP) from the basic PEEP value to another PEEP value comprises reducing the PEEP from the basic PEEP value by a product of the expiratory gas flow times one of the plurality of provided patient exhalation resistance values corresponding in time to the determined expiratory gas flow.

5. A device for controlling an expiratory gas flow in an exhalation path of a ventilator, the device comprising: a user interface; an exhalation valve at the user interface, the exhalation valve providing a positive end-expiratory pressure (PEEP); a gas flow-measuring unit at the user interface; and a control device configured to control the exhalation valve, wherein the control device comprises: a determination module configured to: determine the expiratory flow based on measured data of the gas-flow measuring unit, and determine total exhalation resistance values at points in time of said phase of exhalation and provide a plurality of patient exhalation resistance values by subtracting an estimate of partial exhalation resistance of components in an exhalation path of the ventilator from each of the determined total exhalation resistance values; a change module configured to change the positive end-expiratory pressure (PEEP) during said phase of exhalation with the exhalation valve, wherein the change to the positive end-expiratory pressure comprises reducing the PEEP from the basic PEEP value by a value corresponding to a product of the determined expiratory gas flow times and one of the plurality of provided patient exhalation resistance values corresponding in time to the determined expiratory gas flow.

6. A device in accordance with claim 5, wherein the control device is configured to carry out a method comprising the steps of: during said phase of exhalation, changing, with the exhalation valve, the positive end-expiratory pressure (PEEP) from the basic PEEP value to another PEEP value; during said phase of exhalation, returning, with the exhalation valve, the positive end-expiratory pressure (PEEP) to the basic PEEP; during said phase of exhalation, determining an exhalation parameter comprising an exhalation resistance; and during said phase of exhalation determining expiratory gas flow, wherein the step of changing the positive end-expiratory pressure (PEEP) from the basic PEEP value to another PEEP value comprises reducing the PEEP from the basic PEEP value by a product of the expiratory gas flow times and one of the plurality of provided patient exhalation resistance values corresponding in time to the determined expiratory gas flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic view of a ventilator with an exhalation valve at a user interface;

(3) FIG. 2a is a schematic diagram view showing an increase in the expiratory gas flow;

(4) FIG. 2b is a schematic diagram view showing an increase in the expiratory gas flow;

(5) FIG. 3a is a schematic diagram view showing an initial increase in the expiratory gas flow to avoid air trapping;

(6) FIG. 3b is a schematic diagram view showing an initial increase in the expiratory gas flow to avoid air trapping;

(7) FIG. 4a is a schematic diagram view showing a brief reduction of the PEEP;

(8) FIG. 4b is a schematic diagram view showing a brief reduction of the PEEP;

(9) FIG. 5a is a schematic diagram view showing a brief increase in the PEEP; and

(10) FIG. 5b is a schematic diagram view showing a brief increase in the PEEP.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) Referring to the drawings, a ventilator is designated in its entirety by the reference number 1 in FIG. 1. It has a blower unit 10 with a fan 17, which blower unit 10 is connected to a patient 2 via a user interface 16.

(12) The user interface 16 comprises a tube 13, which is connected to a gas flow-measuring unit 14, a Y-piece 15, which is connected with one end to the gas flow-measuring unit 14, and an exhalation valve 11, which is connected to a second end of the Y-piece 15. The last end of the Y-piece 15 is fluid-communicatingly connected to a fan 17 of the blower unit 10 via a tube 12.

(13) As an alternative, the user interface 16 may be configured as a mask, as a nasal mask or also in another form, the user interface 16 always comprising an exhalation valve 11.

(14) The ventilator 1 further comprises a control device 18, which transmits control signals to the exhalation valve 11 and to the fan 17, as well as received measured signals from the gas flow-measuring unit 14. The control device 18 determines the expiratory gas flow on the basis of the measured data of the gas flow-measuring unit 14. The control device 18 controls the exhalation valve 11 during the phase of exhalation on the basis of the data of the gas flow-measuring unit 14. Further, the control device 18 can actuate the exhalation valve 11 during a phase of exhalation with predefined maneuvers and then detect the change in the expiratory gas flow in the same phase of exhalation by means of the gas flow-measuring unit 14.

(15) The control device 18 comprises for this a change module 182, which transmits change signals to the exhalation valve 11. The change signals cause the exhalation valve 11 to set a PEEP deviating from a basic PEEP value 31.

(16) To detect the measured signals of the gas flow-measuring unit 14, the control device 18 has a determination module 180. The determination module 180 is further configured to receive pressure signals from pressure sensor 19. The determination module 180 can determine additional parameters, e.g., the exhalation resistance, from the transmitted signals.

(17) A plurality of exhalation parameters are plotted over time in FIG. 2a. The rectangular curve drawn in solid line presents the exhalation valve pressure 3 over time. A high exhalation valve pressure 3 shows a phase of inhalation, while a low exhalation valve pressure 3 indicates a phase of exhalation. The exhalation valve pressure 3 is not 0 mbar during the phase of exhalation, but it amounts to a few mbar, which corresponds to the PEEP. The difference between the maximum and the minimum of the exhalation valve pressure 3 is the first pressure difference 30. The minimum of the exhalation valve pressure 3 in FIG. 2a corresponds to the basic PEEP value 31.

(18) The airway pressure 4, which becomes established in the lungs of the patient 2, is represented by the broken line. The airway pressure 4 drops markedly more slowly than the exhalation valve pressure 3 from a maximum during the phase of exhalation to the PEEP.

(19) Further, a first expiratory gas flow 5, which designates the gas flow during the phase of exhalation, is shown by the dash-dot line. The first expiratory gas flow 5 drops to 0 L/sec at the end of the phase of exhalation from a maximum at the beginning of the phase of exhalation. The exhalation valve pressure 3 is controlled by the control unit 18. The first expiratory gas flow 5 is determined by the gas flow-measuring unit 14.

(20) FIG. 2b shows the first expiratory gas flow 5 as a reference in order to illustrate the differences from the second expiratory gas flow 50 described below. Furthermore, the basic PEEP value 31 is drawn as a double dash-dot line to illustrate the differences. The exhalation valve pressure 3 is reduced by a PEEP pressure reduction 6 at the beginning of the phase of exhalation. As a result, the expiratory gas flow is increased, as is indicated by the broken line, which shows the second expiratory gas flow 50. The airway pressure 4 now drops more rapidly than in FIG. 2b. As soon as the control device 18 determines that the airway pressure 4 threatens to drop below the basic PEEP value 31, the exhalation valve pressure 3 is raised again to the basic PEEP valve 31. The drop of the airway pressure 4 takes place more slowly than before beginning from the rise, because the expiratory gas flow is reduced by the rise in the exhalation valve pressure 3.

(21) It is possible in this manner to achieve an increase in the expiratory gas flow 50 at the beginning of the phase of exhalation without the airway pressure 4 of the patient 2 dropping below the PEEP that is meaningful from a physiological point of view.

(22) Knowing the time curve of the airway pressure 4, the airway resistance of the system comprising the ventilator 1 and the patient 2 can be calculated. Further, the compliance of the system can be calculated. The PEEP can be set at the exhalation valve 11 accurately by means of the calculated values by the control device 18 during the same phase of exhalation. The pressure at the exhalation valve 11 may be lower in this case than the desired PEEP, because the PEEP is calculated from the pressure at the exhalation valve 11 in combination with the pressure that is calculated from the expiratory gas flow multiplied by the exhalation resistance.

(23) The averaged exhalation resistance of the system from a plurality of breaths can be used as a basis for the calculation of the optimal pressure at the exhalation valve 11 in order to suppress dynamic changes between different breaths.

(24) In an alternative embodiment, the exhalation resistance can also be estimated with sufficient accuracy in case of known components. The exhalation resistance should be estimated rather as too low than as too high in order not to risk a PEEP that is too low for the patient 2.

(25) FIG. 3a shows a situation in which the expiatory gas flow is not sufficient during the phase of exhalation to allow the entire breath volume to flow out of the lungs during the phase of exhalation. The phase of inhalation thus starts too early. The expiratory gas flow is designated here as the third expiratory gas flow 51, which is relatively low and has a flat course compared to the first expiratory gas flow 5 shown in FIG. 2a. An air trapping indication 52 can be seen at the end of the phase of exhalation. The air trapping indication 52 arises from the fact that the expiratory gas flow 51 does not drop to 0 L/sec at the end of the phase of exhalation but remains at a value greater than 0 L/sec. This indicates that the PEEP was estimated to be too high or the exhalation resistance is higher than assumed.

(26) Air remains in the lungs of the patient 2 after each phase of exhalation due to the air trapping. In ventilation modes in which the respiratory minute volume is maintained at a constant value during the inhalation, the same volume is introduced into the lungs of the patient 2 during each phase of inhalation. Due to the air trapping, there remains an offset, which increases with each breath, after each phase of exhalation, so that the residual volume in the lungs increases with each phase of inhalation.

(27) FIG. 3b shows a maneuver that corresponds to the maneuver in FIG. 2b, and air trapping is avoided according to FIG. 3b. The exhalation valve pressure 3 is reduced for this to far below the desired PEEP at the beginning of the phase of exhalation. This is represented by the PEEP pressure drop 6. There is a fourth expiratory gas flow 53 during this time, which rapidly transports the breath volume from the lungs. The third expiratory gas flow 51, which is markedly lower at the beginning of the phase of exhalation than the fourth expiratory gas flow 53, is additionally shown for comparison. Further, the fourth expiratory gas flow 53 drops markedly below the first expiratory gas flow 51 at the end of the phase of exhalation. As soon as the airway pressure 4, which is not shown in FIG. 3b, threatens to drop below the PEEP, the exhalation valve pressure 3 is again raised to the basic PEEP value 31. As can be seen in FIG. 3b, the fourth expiratory gas flow 53 drops to 0 L/sec at the end of the phase of exhalation, so that the lungs were completely freed of the breath volume. Air trapping is avoided hereby.

(28) Like FIG. 2a, FIG. 4a shows a reference curve, which is used to illustrate the differences of the curves shown in FIG. 4b.

(29) FIG. 4b shows an embodiment of the method with which the differential value can be calculated for the exhalation resistance and the compliance at the tidal volume or state of distension of the lungs that are present at this time. The exhalation valve pressure 3 is briefly reduced for this within a pressure reduction period 35. The pressure reduction period 35 is very short relative to the entire phase of exhalation. It may be in the range of 10-30 msec.

(30) Due to the brief reduction of the exhalation valve pressure 3, the first expiratory gas flow 5 is briefly increased with an expiratory gas flow increase 57. Due to the drop of the PEEP during the pressure reduction period 35, the pressure at the exhalation valve 11 corresponds to the product of the expiratory gas flow times the exhalation resistance at this point of the tidal volume. The particular exhalation resistance can therefore be determined in this manner at different points of the tidal volume, i.e., for different states of distension of the lungs. Further, the compliance can thus be determined as a function of the tidal volume of the lungs.

(31) Like FIGS. 2a and 4a, FIG. 5a shows a reference diagram.

(32) FIG. 5b shows an arbitrary brief interruption of the first expiratory gas flow 5, which is due to the exhalation valve pressure 3 being briefly raised to the inhalation pressure within a pressure increase period 34. An airway pressure increase 40 now becomes established based on the briefly reduced expiratory gas flow 56. The compliance of the lungs can be calculated based on the rise (in airway pressure 40) during the measurement period 42 and by means of the airway pressure difference 41.

(33) This method is suitable above all for a measurement of the compliance during spontaneous breathing or assisted ventilation. It was impossible or difficult to determine the compliance during spontaneous breathing or assisted ventilation before.

(34) The shorter the pressure increase period 34, the more accurately can the compliance be determined for a defined tidal volume, because the respiratory parameters differ only slightly before and after the pressure increase period 34 based on the only brief change in the exhalation valve pressure 3.

(35) If a major airway pressure difference 41 develops, there may an indication of a high intrinsic overpressure in the lungs or of a high active work of exhalation on the part of the patient 2. Both represent important information in relation to the ventilation situation and a possible exhaustion and hence an unsuccessful weaning from the ventilator (weaning).

(36) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.