PROCESS FOR SUPPORTING BLOOD GAS EXCHANGE BY VENTILATION AND EXTRACORPOREAL BLOOD GAS EXCHANGE AND SYSTEM OPERATING ACCORDING TO THE PROCESS

Abstract

A system (10) for supporting the blood gas exchange of a patient (12) by means of a ventilator (14) as well as by means of a CO.sub.2 removal device (16), and a process for operating such a system (10), wherein a measured value concerning an expiratory or end-expiratory CO.sub.2 concentration in the breathing gas of the patient (12) can be detected by means of a sensor system (20), wherein a measured value can be selected as a start value by means of an operating action, wherein a trend parameter can be determined with the start value and with a respective, currently determined measured value and wherein a difference of a set point for the trend parameter and a respective, current value of the trend parameter can be fed to a controller (42), which acts on the CO.sub.2 removal device.

Claims

1. A system for supporting a blood gas exchange of a patient by means of ventilation as well as by means of extracorporeal blood gas exchange by CO.sub.2 removal, the system comprising: a medical device in the form of a ventilator; a medical device in the form of a CO.sub.2 removal device for the extracorporeal blood gas exchange; a controller configured to act on the CO.sub.2 removal device; and a sensor system configured to detect a measured value concerning an expiratory CO.sub.2 concentration in the breathing gas of the patient, wherein a current measured value is selectable as a start value by means of an operating action at the system, wherein: a difference of the start value and a respective current measured value is fed to the controller, which acts on the CO.sub.2 removal device based on the difference; or a difference of a trend parameter formed with the start value and a set point for the trend parameter is fed to the controller, which acts on the CO.sub.2 removal device.

2. A system in accordance with claim 1, wherein the sensor system is further configured to detect an end-expiratory CO.sub.2 concentration in the breathing gas of the patient as the measured value concerning the expiratory CO.sub.2 concentration in the breathing gas of the patient.

3. A system in accordance with claim 1, wherein the trend parameter is determined with the start value and with the measured value which is a currently determined, and wherein a difference of a set point for the trend parameter and the respective current value of the trend parameter is fed to the controller, which acts on the CO.sub.2 removal device.

4. A system in accordance with claim 3, wherein the trend parameter is determined in the form of a standardization of the respective, currently determined measured values in relation to the start value.

5. A system in accordance with claim 1, further comprising a display unit, wherein the measured value currently determined is outputted at the display unit and the displayed measured value is selected as a start value by means of the operating action.

6. A system in accordance with claim 1, wherein a spontaneous respiratory rate of the patient is monitored by means of the sensor system and a signal element is actuated in case a predefined or predefinable threshold value is exceeded.

7. A system in accordance with claim 1, wherein a weaning mode is activated by means of an operating action on the system, and wherein a CO.sub.2 removal target is reduced automatically and in a controlled manner in the weaning mode.

8. A system in accordance with claim 7, wherein an influence of the controller on the CO.sub.2 removal device is deactivated at a beginning of the reduction of the CO.sub.2 removal target, wherein the trend parameter is monitored in relation to a predefined or predefinable tolerance range during the reduction of the CO.sub.2 removal target, and wherein the influence of the controller on the CO.sub.2 removal device is reactivated in case of a moving out of the tolerance range, and the reduction of the CO.sub.2 removal target is deactivated.

9. A process for operating a system for supporting a blood gas exchange of a patient by means of ventilation as well as by means of extracorporeal blood gas exchange by a CO.sub.2 removal wherein the system comprises: a medical device in the form of a ventilator; a medical device in the form of a CO.sub.2 removal device for the extracorporeal blood gas exchange; a controller configured to act on the CO.sub.2 removal device; and a sensor system configured to detect a measured value concerning an expiratory CO.sub.2 concentration in the breathing gas of the patient, wherein a current measured value is selectable as a start value by means of an operating action at the system wherein: a difference of the start value and a respective current measured value is fed to the controller, which acts on the CO.sub.2 removal device based on the difference; or a difference of a trend parameter formed with the start value and a set point for the trend parameter is fed to the controller, which acts on the CO.sub.2 removal device, the process comprising the steps of: detecting a measured value concerning an expiratory CO.sub.2 concentration in the breathing gas of the patient by means of the sensor system; selecting measured value which is current as the start value by means of an operating action at the system; and feeding: a difference of the start value and a respective current measured value to a controller, which acts on the CO.sub.2 removal device; or a difference of a trend parameter formed with the start value and a set point for the trend parameter to the controller, which acts on the CO.sub.2 removal device.

10. A process in accordance with claim 9, wherein the trend parameter is determined with the start value and the measured value which is currently determined, and wherein a difference of a set point for the trend parameter and the trend parameter currently determined is fed to the controller, which acts on the CO.sub.2 removal device.

11. A process in accordance with claim 10, wherein the trend parameter is determined in the form of a standardization of the measured value currently determined in relation to the start value.

12. A process in accordance with claim 9, wherein the respective current measured value is outputted on a display unit and the displayed measured value is selected as the start value by means of the operating action.

13. A process in accordance with claim 9, wherein a spontaneous respiratory rate of the patient is monitored by means of the sensor system and a signal element is actuated in case a predefined or predefinable threshold value is exceeded.

14. A process in accordance with claim 9, wherein a weaning mode is activated by means of an operating action on the system, and wherein a CO.sub.2 removal target is reduced automatically and in a controlled manner in the weaning mode.

15. A process in accordance with claim 14, wherein an influence of the controller on the CO.sub.2 removal device is deactivated at a beginning of the reduction of the CO.sub.2 removal target, wherein the trend parameter is monitored in reference to a predefined or predefinable tolerance range during the reduction of the CO.sub.2 removal target and wherein the influence of the controller on the CO.sub.2 removal device is reactivated and the reduction of the CO.sub.2 removal target is deactivated, on the other hand, in case of a moving out of the tolerance range.

16. A process according to claim 9, further comprising confirming a presence of an acceptable CO.sub.2 concentration in the breathing gas by an operator of the system by an operating action; regulating operation of the CO.sub.2 removal device to or toward a CO.sub.2 concentration characterized as being acceptable upon such an operating action and wherein removal of carbon dioxide from the blood of the patient is carried out during the regulated operation of the CO.sub.2 removal device.

17. A process according to claim 9, wherein a computer program with program code is provided to carry one or more of the steps with the control program run by a processing unit one or more of the medical devices.

18. A system in accordance with claim 1, wherein one or both of the medical devices provide a processing means detecting a measured value concerning an expiratory CO.sub.2 concentration in the breathing gas of the patient by means of the sensor system; selecting the measured value which is current as the start value by means of an operating action at the system; and feeding: a difference of the start value and a respective current measured value to a controller, which acts on the CO2 removal device; or a difference of a trend parameter formed with the start value and a set point for the trend parameter to the controller, which acts on the CO.sub.2 removal device.

19. A process in accordance with claim 9, wherein the sensor system is further configured to detect the measured value concerning the expiratory CO.sub.2 concentration in the breathing gas of the patient comprises an end-expiratory CO.sub.2 concentration in the breathing gas of the patient.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In the drawings:

[0059] FIG. 1 is a schematic view of a system for ventilating a patient, which comprises at least one medical device acting as a ventilator;

[0060] FIG. 2 is a schematic view of a device acting as a control unit in the system according to FIG. 1;

[0061] FIG. 3 is a schematic view of a control circuit for regulating the extracorporeal blood gas exchange of a patient;

[0062] FIG. 4 is a schematic view of a curve describing the weaning of a patient from an extracorporeal blood gas exchange; and

[0063] FIG. 5 is a flow chart for illustrating a process taking place during the weaning according to FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0064] Referring to the drawings, the view in FIG. 1 shows, in a highly simplified, schematic form, a system 10 for supporting a gas exchange in a patient 12. The system 10 comprises at least two medical devices 14, 16, namely, a first medical device 14 in the form of a ventilator for the mechanical ventilation of the lungs of the patient 12 and a second medical device 16 for extracorporeal blood gas exchange. At least a removal of carbon dioxide (CO.sub.2) from the blood of the patient 12 and possibly an enrichment of the blood with oxygen (02) are carried out by means of the second medical device 16. The first medical device 14 acting as a ventilator will hereinafter be called, for short, but without abandoning a further general validity, a ventilator 14. The second medical device 16 intended at least for the removal of carbon dioxide from the blood of the patient 12 will correspondingly be called for short, likewise without abandoning a further general validity, a CO.sub.2 removal device 16. Devices 14, 16 of the above-mentioned type are known per se. A CO.sub.2 removal device 16 is also called at times ECCO.sub.2R for short in the technical literature.

[0065] The ventilator 14 is connected in the manner known per se non-invasively to the lungs of the patient 12, for example, by means of a breathing mask 18. The CO.sub.2 removal device 16 is likewise connected in the manner known per se to the blood circulation of the patient 12.

[0066] A measured value concerning an expiratory or end-expiratory CO.sub.2 concentration in the breathing gas of the patient can be detected by means of a sensor system 20 comprising at least a CO.sub.2 sensor, for example, a sensor system 20 located in the breathing mask 18 in the manner known per se, during the operation of the ventilator 14 and, on the whole, during the operation of the system 10. This measured value will hereinafter be called at times etCO.sub.2mess for short.

[0067] One of the at least two medical devices 14, 16, for example, the ventilator 14, acts within the system 10 as a higher-level device or the system 10 comprises a dedicated higher-level device or an additional medical device 22 acting as a higher-level device and as a control unit. The following description will be continued on the basis of a system 10 with such an additional medical device 22 and this is called a control device 22. It is just as well considered, in principle, that the system 10 does not comprise any such additional medical device 22 and that the ventilator 14 or even the CO.sub.2 removal device 16 acts instead as a control unit. This shall always be implied in the following whenever a higher-level device or a control unit is mentioned. In case of a separate control unit 22, this is connected communicatively in the manner known, in principle, per se to the other devices 14, 16 of the system 10 at least for the exchange of data, especially in the form of measured values and/or control signals. In the case of a system 10 without such a separate control unit, the device 14, 16 acting as a control unit is connected to the other devices 14, 16 of the system in the manner outlined above.

[0068] The device acting as a control unit 22 comprises in the embodiment shown a display unit 24 as well as an input device 26 or is connected to a device or devices with a display unit 24 and/or with an input device 26 in the manner known, in principle, per se. The measured value (etCO.sub.2mess) that can be regularly recorded by means of the sensor system 20 and is regularly recorded during the operation of the system 10 is outputted to the system 10 and is processed within the system 10. A display unit 24 is optional. The output of the measured value is carried out directly or indirectly to the device acting as a control unit 22 and the processing of the measured value comprises, in case of an existing display unit 24, at least a display of the measured value by means of the display unit 24. The display of the measured value by means of the display unit 24 makes it possible for an operator of the system 10, usually a physician, to monitor the measured value. Without such a display of the measured value, the operator evaluates the patient 12 himself, i.e., for example, his breathing behavior. When the operator finds a satisfactory breathing behavior of the patient 12 and/or a measured value in an acceptable range or a measured value that remains stable over a sufficiently long time period in an acceptable range, which measured value is outputted by means of the display unit 24, he carries out an operating action on the system 10. It is expressed by means of the operating action that a satisfactory breathing behavior and/or an acceptable displayed measured value are present. In case of a satisfactory breathing behavior as the only criterion for performing the operating action, it can be assumed that the measured value (etCO.sub.2mess) recorded by means of the sensor system 20—independently from a possible display by means of the display unit 24—is likewise an acceptable measured value or a measured value in an acceptable range. The recorded, current and optionally displayed measured value can be selected as a start value for a reproducible extracorporeal CO.sub.2 removal by means of the CO.sub.2 removal device 16, which takes place according to the principle being proposed here by means of the operating action, for example, an operating action in the form of an actuation of the input device 26.

[0069] The view in FIG. 2 shows likewise in a schematically highly simplified manner the device acting as a control unit 22 in the system 10 (FIG. 1), i.e., for example, the additional medical device 22, where the additional medical device 22 may be, for example, a medical device in the form of a therapy device or the like, which is associated with or is hierarchically at a higher level than the ventilator 14 and the CO.sub.2 removal device 16. The control unit 22 comprises the (optional) display unit 24 and the input device 26. These may be each elements of a user interface represented by means of a monitor of the control unit 22 in a manner known basically per se. The control unit 22 comprises, furthermore, a processing unit 30 in the form of or in the manner of a microprocessor as well as a memory 32, into which a control program 34 is loaded, which is executed by means of the processing unit 30 during the operation of the control unit 22. For example, the display of the user interface and the analysis of operating actions, which pertain to the user interface, if the control unit 22 uses such a user interface, also take place under the control of the control program 34. At any rate, the actuation of the display unit 24 and hence the display of the measured values and the analysis of the input device 26 for detecting possible operating actions also take place under the control of the control program 34.

[0070] If a measured value recorded by means of the sensor system 20 was selected as an acceptable measured value by such an operating action, either based on an observation of the patient 12 or on the basis of an observation of the display unit 24, this measured value is recorded as a start value, for example, in a start value storage location 36 in the memory 32 and is loaded to this end into the start value storage location 36.

[0071] The view in FIG. 3 shows a control circuit 40 for the implementation of the regulation explained in the general part of the description for stabilizing a trend parameter, which is based on a respective, currently determined measured value (preservation regulation). The following description correspondingly applies to a regulation for stabilizing the start value, and a regulation, whose goal is to stabilize the start value instead of a stabilization of the trend parameter, shall always be implied.

[0072] The control circuit 40 comprises, in the manner known, in principle, per se, a controller 42, for example, a P controller, a PI controller or a PID controller, preferably a PI controller. The controller 42 acts on the CO.sub.2 removal device 16 and the control system is formed by the CO.sub.2 removal device 16 and by the patient 12. The CO.sub.2 removal device 16 acts on the patient 12 with a CO.sub.2 removal rate (CO.sub.2Ri). The CO.sub.2 removal device 16 is actuated in the manner known per se with a CO.sub.2 removal target (CO.sub.2Rt) acting as a set point for the CO.sub.2 removal. The CO.sub.2 removal device 16 is actuated within the control circuit 40 by the controller 42. The controller 42 consequently predefines the CO.sub.2 removal target as the manipulated variable.

[0073] The measured value determined in the control circuit 40, namely at the patient 12, is the measured value concerning the expiratory or end-expiratory CO.sub.2 concentration (etCO.sub.2mess), which is determined in the breathing gas exhaled by the patient by means of a sensor system 20 (FIG. 1) known, in principle, per se. The measured value is standardized in the return branch of the control circuit 40 with a measured start value 44 (etCO.sub.2mess(0)) determined prior to the activation of the regulation and polled, for example, from the start value storage location 36 to obtain a trend parameter (etCO.sub.2equal). This is carried out by means of a standardizing unit 46. The standardization by means of the standardizing unit 46 comprises the quotient formation explained in the general part of the description. The trend parameter is determined now with the respective current measured value concerning the expiratory or end-expiratory CO.sub.2 concentration (etCO.sub.2mess(k)) and the start value 44. For example, the value 1.0 or the value 100% acts as a command variable/set point.

[0074] The deviation (AetCO.sub.2equal) is obtained by subtraction in a manner known, in principle, per se with the command variable and with the trend parameter returned in the return branch. If the trend parameter determined on the basis of the respective detected expiratory or end-expiratory CO.sub.2 concentration deviates from the set point, the regulation comes into action by the controller 42 changing the CO.sub.2 removal target. The intervention of the controller 42 takes place now by the set point for the CO.sub.2 removal rate (CO.sub.2 removal target) being increased in case of an increase in the trend parameter. As a result, the CO.sub.2 content drops in the blood. This leads to a reduction of the respiratory drive of the patient 12. An increase in the trend parameter is equivalent (because etCO.sub.2equal=etCO.sub.2mess(k)/etCO.sub.2mess(0)) to an increased expiratory or end-expiratory CO.sub.2 concentration (etCO.sub.2mess(k)) in the breathing gas of the patient 12 compared to the start value (etCO.sub.2mess(0)).

[0075] An optional improvement concerning the detection of an indicator for the expiratory or end-expiratory CO.sub.2 concentration in the breathing gas of the patient 12 may be, for example, that an estimated value is determined for etCO.sub.2mess under ideal measurement conditions, i.e., more or less an ideal measured value is obtained, on the basis of information on inspiratory efforts, which may be indicated, for example, by the spontaneous respiratory rate (f.sub.spontan) and/or by the I:E ratio. This ideal measured value will hereinafter be called etCO.sub.2ideal. The information concerning the spontaneous respiratory rate (f.sub.spontan) and the I:E ratio (I:E) may originate either from an additional sensor system or from a flow sensor integrated into the sensor system 20 (FIG. 1) or directly from the breathing phase detection by the CO.sub.2 sensor. Under the assumption that the ventilation of the patient 12 takes place with a negligibly low inspiratory CO.sub.2 concentration, the following estimated value is obtained for etCO.sub.2ideal under the assumption of constant inspiratory and expiratory CO.sub.2 concentrations:

etCO.sub.2ideal=CO.sub.2(exsp)+CO.sub.2(insp)*(I:E).

[0076] The following formula, in which the entire CO.sub.2 concentration measured during a breath (T) is added to the exhalation phase (Te), can be used in the general case of CO.sub.2 concentrations variable over time, CO.sub.2(t):

[00001]${\mathrm{et}.Math.\mathrm{CO}}_2.Math.\mathrm{ideal}=\frac{1}{\mathrm{Te}}.Math.{\int }_0^T.Math.{\mathrm{CO}}_2\left(t\right).Math.\mathrm{dt}$

Here, Te is the duration of the exhalation and T is the duration of the breath, i.e., T=Ti+Te and T=1/f.

[0077] In the limit case of a disappearing inspiratory CO.sub.2 concentration, this leads, as expected, to:

[00002]$\mathrm{et}.Math..Math.{\mathrm{CO}}_2=\frac{1}{\mathrm{Te}}.Math.{\int }_0^{\mathrm{Te}}.Math.{\mathrm{CO}}_2\left(t\right).Math.\mathrm{dt}={\mathrm{CO}}_2\left(\mathrm{exsp}\right)$

In the limit case of equal inspiratory and expiratory concentrations (greatly smoothed measured values), we obtain:

[00003]${\mathrm{et}.Math.\mathrm{CO}}_2=\frac{1}{\mathrm{Te}}.Math.{\int }_0^T.Math.{\mathrm{CO}}_2.Math..Math.\mathrm{dt}=\frac{T}{\mathrm{Te}}.Math.{\mathrm{CO}}_2=\left(1+l:E\right).Math..Math.{\mathrm{CO}}_2$

It is assumed in each case that the non-disappearing CO.sub.2 concentration during the inhalation represents a measurement artifact, so that a correction of etCOmess to etCO.sub.2ideal is favorable.

[0078] The calculation of etCO.sub.2equal is carried out, analogously to the above-described calculation, by standardization to the start value of etCO.sub.2ideal, which is categorized as being medically acceptable:

[00004]${\mathrm{et}.Math.\mathrm{CO}}_2.Math.\mathrm{equal}.Math..Math.\left(k\right)=\frac{{\mathrm{et}.Math.\mathrm{CO}}_2.Math.\mathrm{ideal}\left(k\right)}{{\mathrm{et}.Math.\mathrm{CO}}_2.Math.\mathrm{ideal}\left(k=0\right)}$

[0079] Independently from the use of etCO.sub.2mess or etCO.sub.2ideal, the time k=0 is the “initial time” at which the patient 12 is evaluated by the physician as “o.k.” More complicated forms of the calculation of etCO.sub.2equal with the inclusion of the spontaneous respiratory rate as a weighting factor or for case differentiation are likewise possible and useful. The controller 42, the processing of the measured values, the return in the control circuit 40 and the determination of the deviation at the input of the controller 42 are preferably implemented in software. The corresponding details of the view in FIG. 3 thus show a part of the functionality of the control program 34 of the control unit 22. The spontaneous respiratory rate (f.sub.spontan) of the patient 12 can optionally be monitored by means of a corresponding sensor system (not shown), which is known, in principle, per se. A significant change, i.e., a change in the spontaneous respiratory rate exceeding a predefined or predefinable threshold value (for example, a value exceeding a spontaneous respiratory rate of 30 per minute), during the above-described preservation regulation, may suggest an impairment of the quality of the measurement of the expiratory or end-expiratory CO.sub.2 concentration (etCO.sub.2mess(k)). The respective measured value is directly included in the determination of the trend parameter and the quality of the measured value thus determines the quality of the preservation regulation. It is therefore optionally proposed that in case of a sensory monitoring of the spontaneous respiratory rate in case of a change in the spontaneous respiratory rate exceeding a predefined or predefinable threshold value, an alarm be automatically triggered, for example, by means of an optical and/or acoustic signal element. Based on such an alarm, the operating staff can check, for example, the fitting of a ventilation mask or the like and correct it if necessary.

[0080] In such an optional embodiment, the analysis of a measured value coding the spontaneous respiratory rate and the monitoring of the measured value in reference to the threshold value is preferably likewise implemented as a part of the functionality of the control program 34 of the control unit 22. Taken by itself, the comparison of a measured value with a threshold value and the actuation of a signal element in case a threshold value is exceeded are trivial and corresponding functional elements or program code instructions are not shown here accordingly.

[0081] In addition or as an alternative, an automatically supported “weaning” of the patient 12 from the support by the CO.sub.2 removal device 16 may be optionally provided. The beginning of such a weaning is activated by the operator of the system 10 (FIG. 1), for example, in the form of an operating action, for example, of an actuation of an input device 26, especially of an additional input device (key, switch, element of a user interface or the like). The system 10 then switches into a weaning mode. The preservation regulation (FIG. 3) is at first deactivated in the weaning mode. The weaning mode is characterized in that the CO.sub.2 removal target (CO.sub.2Rt) is reduced by a predefined or predefinable value, for example, by 3 mL/minute per hour. The current values of the trend parameter etCO.sub.2equal continue to be determined and monitored continuously in the weaning mode. When the respective current value of the trend parameter moves out of a predefined or predefinable tolerance range, for example, 100%±10%, the preservation regulation is reactivated (and the CO.sub.2 removal target is possibly increased again at the same time).

[0082] The preservation regulation reactivated on the basis of a moving out of the tolerance range remains active until the trend parameter etCO.sub.2equal, which continues to be determined currently, has once reached the set point, i.e., for example, 100%, or until currently determined trend parameters etCO.sub.2equal remain within the tolerance range or within an preservation regulation tolerance range that is “narrower” than the tolerance range, for example, 100%±2%, 100%±3%, 100%±5%, etc., during a predefined or predefinable time period. The preservation regulation is then deactivated again automatically, and the reduction of the removal target for the CO.sub.2 removal (CO.sub.2Rt) by the above-mentioned predefined or predefinable value and starting from the value for the CO.sub.2 removal target valid during the deactivation of the preservation regulation starts again.

[0083] A multiple switching may take place between the reduction of the CO.sub.2 removal target (CO.sub.2Rt) and the automatic reactivation of the preservation regulation during the operation of the system 10 in the weaning mode.

[0084] The view in FIG. 4 shows as a function of the time t plotted in hours a possible curve of weaning, namely, a curve of the trend parameter (etCO.sub.2equal) in the upper area and a curve of the CO.sub.2 removal target (CO.sub.2Rt) in the lower area. The value range of the curve of the trend parameter is plotted on the ordinate in percentage values (50%, 100%, 150%). The value range of the curve of the CO.sub.2 removal target (CO.sub.2Rt) is not shown additionally on the ordinate. The graph of the CO.sub.2 removal target starts in the example shown at 80 mL/minute and ends at 20 mL/minute.

[0085] According to the situation shown as an example in FIG. 4, the weaning mode is activated at the time t=0. The CO.sub.2 removal target drops at first (time period I) correspondingly. The trend parameter etCO.sub.2equal, which continues to be determined, does, however, rise and increase so much that it moves beyond an upper limit of a tolerance range, which is shown by two horizontal broken lines and is marked here as an example at 100%±25%. The width of the tolerance range is predefined or predefinable and optionally adjustable. The tolerance range does not necessarily have to extend symmetrically around 100%. In case of a moving out of the tolerance range, the preservation regulation is reactivated. This brings about in the example shown a rise in the CO.sub.2 removal target (time period II). The reactivation of the preservation regulation ends in the example shown with the return of the trend parameter etCO.sub.2equal into the tolerance range.

[0086] Other criteria for the ending of the reactivated preservation regulation are likewise possible alternatively (see above). After the preservation regulation has been again deactivated, the reduction of the CO.sub.2 removal target (CO.sub.2Rt) begins again. The reduction lasts during the time period III and ends when the CO.sub.2 removal target (CO.sub.2Rt) reaches a predefined or predefinable lower limit value. The CO.sub.2 removal device 16 subsequently continues to operate with the CO.sub.2 removal target reached last until the CO.sub.2 removal device 16 is deactivated and removed by the operator of the system 10.

[0087] The view in FIG. 5 illustrates the weaning mode as was described above on the basis of a schematically simplified flow chart.

[0088] The weaning mode is activated by an operating action of a user (block 50). The preservation regulation is deactivated at first (block 52) in the weaning mode. It is then checked (block 54) whether a CO.sub.2 removal target (CO.sub.2Rt) to be reduced in the weaning mode has already reached a predefined or predefinable lower limit value. This cannot normally be the case immediately after the activation of the weaning mode. The condition is not consequently met normally and carrying out of the “minus” branch will correspondingly follow and the CO.sub.2 removal target is subsequently reduced (block 56). It is then checked (block 58) whether the trend parameter is still within the tolerance range. As long as this is the case (“plus” branch), the process is branched off before block 54. It is checked there whether the lower limit value for the CO.sub.2 removal target has already been reached (block 54), and as long as it is not the case, the removal target is reduced (block 56) and the trend parameter is then checked relative to the tolerance range (block 58). As long as the trend parameter remains in the tolerance range and the limit value for the CO.sub.2 removal target is not yet reached, the CO.sub.2 removal target is reduced by means of this partial functionality, and the view in the schematically simplified flow chart does not take into consideration the circumstance that the reduction preferably takes place at a predefined rate of reduction per unit of time, for example, 3 mL/minute per hour. When it is determined during the reduction of the CO.sub.2 removal target (block 54) that the limit value for the CO.sub.2 removal target is reached, the weaning mode ends (block 60) and the CO.sub.2 removal target is not reduced further. It may, however, happen during the reduction of the CO.sub.2 removal target (blocks 54, 56, 58) that a checking of the trend parameter in relation to the tolerance range (block 58) reveals that the trend parameter has left the tolerance range. The preservation regulation is then activated (block 62) (“minus” branch) and the preservation regulation is subsequently carried out (block 64). It is checked during the action of the preservation regulation (block 66) whether the trend parameter meets a predefined or predefinable quality criterion. The quality criterion may be defined, for example, such that the trend parameter must have returned again into the tolerance range, it must have reached a predefined or predefinable value, for example, 100%, at least once, or the like (see above). When this happens (“plus” branch), the process is branched off for the renewed deactivation of the preservation regulation (block 52), and the reduction of the CO.sub.2 removal target will then begin again. As long as the trend parameter does not meet the quality criterion (“minus” branch), the preservation regulation (block 64) is carried out.

[0089] Whenever predefined or predefinable values are mentioned above, these are preferably basically variable data, which are stored in the memory 32 of the control unit 22 and the frameworks of the execution of the process or of individual embodiments of the process are automatically accessed. Predefined values are selected, for example, at the time of delivery or during the first use of the control unit 22 and loaded into the memory 32. Predefinable values are values that can also be changed, for example, during the operation of the control unit 22 or between consecutive uses of the control unit 22 by an operator of the control unit 22 or by an operator of the system 10, especially a physician, in terms of a parameterization.

[0090] Individual prominent aspects of the description being submitted here can thus be briefly summarized as follows: Proposed are a system 10 for supporting the blood gas exchange of a patient 12 by means of a ventilator 14 as well as by means of a CO.sub.2 removal device 16, and a process for operating such a system 10, wherein a measured value concerning an expiratory or end-expiratory CO.sub.2 concentration in the breathing gas of the patient 12 can be detected by means of a sensor system 20, wherein the respective current measured value can be optionally outputted to a display unit 24, wherein a measured value can be selected as a start value by means of an operating action, for example, in the course of an observation of the display of the display unit 24, wherein, for example, a trend parameter can be determined with the start value and with a respective, currently determined measured value, and wherein a difference of a set point for the trend parameter and a respective current value of the trend parameter can be fed to a controller 42, which acts on the CO.sub.2 removal device 16.

[0091] 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.

LIST OF REFERENCE NUMBERS

[0092] 10 System [0093] 12 Patient [0094] 14 Medical device, ventilator [0095] 16 Medical device, CO.sub.2 removal device [0096] 18 Breathing mask [0097] 20 Sensor system [0098] 22 Medical device, control unit [0099] 24 Display unit [0100] 26 Input device [0101] 30 Processing unit [0102] 32 Memory [0103] 34 Control program [0104] 36 Start value storage location [0105] 40 Control circuit [0106] 42 Controller [0107] 44 Start value [0108] 46 Standardizing unit [0109] 50-66 Block (in flow chart)