Method for controlling a device for extracorporeal blood gas exchange, device for extracorporeal blood gas exchange, as well as control device for controlling a device for extracorporeal blood gas exchange

Abstract

A method controls a device for extracorporeal blood gas exchange. The device has a membrane as a gas-liquid barrier between a bloodstream and a gas stream. The membrane further makes possible a passing over of the carbon dioxide content from the bloodstream into the gas stream. The device has at least one actuator. A change in a value of an operating parameter of the actuator brings about a change in a value of the carbon dioxide content that passes over from the bloodstream into the gas stream. The method further includes providing breathing gas information that indicates a carbon dioxide concentration in breathing gas and providing a control signal, which indicates a request for setting a value of the operating parameter and changing of the value of the operating parameter as a function of the carbon dioxide concentration in the breathing gas.

Claims

1. A method for controlling a device for extracorporeal blood gas exchange, wherein the device comprises a membrane as a gas-liquid barrier between a bloodstream and a gas stream, wherein the membrane makes possible a passing of carbon dioxide content over from the bloodstream into the gas stream, at least one actuator, wherein a change in a value of an operating parameter of the actuator brings about a change in a value of the carbon dioxide content, which passes over from the bloodstream into the gas stream, the method comprising the steps of: providing at least one control device comprising an anesthesia device and a capnometer; providing breathing gas information, which indicates a carbon dioxide concentration in a breathing gas; providing a control signal, which indicates a request for setting a value of the operating parameter; changing the value of the operating parameter as a function of the carbon dioxide concentration in the breathing gas; providing at least one minimal value, wherein in case the value of the at least one operating parameter reaches the minimal value, the value of the at least one operating parameter is retained; and stopping a weaning process when the value of the at least one operating parameter reaches the minimal value.

2. A method in accordance with claim 1, wherein the operating parameter has an effect on a pumping capacity of a pump that is a part of or is associated with the device.

3. A method in accordance with claim 1, wherein the operating parameter has an effect on an oxygen quantity of the gas stream.

4. A method in accordance with claim 1, further comprising the steps of: providing at least one comparison value, which indicates a comparison concentration; and changing of the value of the operating parameter as a function of the carbon dioxide concentration in the breathing gas and of the comparison concentration.

5. A method in accordance with claim 4, wherein in case the carbon dioxide concentration in the breathing gas is higher than the comparison concentration, the value of the at least one operating parameter is changed such that the value of the carbon dioxide content, which passes over from the bloodstream into the gas stream, is reduced.

6. A method in accordance with claim 4, wherein in case the carbon dioxide concentration in the breathing gas is lower than the comparison concentration, the value of the at least one operating parameter is changed such that the value of the carbon dioxide content, which passes over from the bloodstream into the gas stream, is increased.

7. A method in accordance with claim 1, further comprising the steps of: providing at least one piece of information, which indicates an extent of a state of ventilation of a lung; and providing a ventilation threshold value, wherein the retaining of the value of the at least one operating parameter is further made dependent on a comparison of the extent of the state of ventilation with the ventilation threshold value.

8. A method in accordance with claim 1, further comprising the steps of: providing information, which indicates an extent of inspiratory muscle activity; and providing an activity threshold value, wherein the retaining of the value of the at least one operating parameter is further made dependent on a comparison of the extent of the inspiratory muscle activity and on the activity threshold value.

9. A method in accordance with claim 1, further comprising the steps of: providing at least one first blood gas measured value, which corresponds to a first measurement time; providing at least one second blood gas measured value, which corresponds to a second measurement time; and providing an output signal as a function of the first and of the second blood gas measured value.

10. A method in accordance with claim 1, further comprising: providing a control unit, wherein the control unit receives the breathing gas information as input and provides the control signal as output, the at least one actuator receiving the control signal as input.

11. A device for extracorporeal blood gas exchange, the device comprising: a bloodstream guide area for guiding a bloodstream; a gas-guiding area for guiding a gas stream; a membrane forming a gas-liquid barrier between the bloodstream guided in the bloodstream guide area and the gas stream guided in the gas-guiding area for passing over of carbon dioxide content from the bloodstream into the gas stream; a data network interface; at least one actuator operating based on an actuator operating parameter, the actuator operating parameter having a value that determines a value of the carbon dioxide content which passes over from the bloodstream into the gas stream; and at least one control unit comprising a capnometer and an anesthesia device, the at least one control unit being configured: to receive a control signal by means of the data network interface, the control signal indicating a request for setting the value of the actuator operating parameter; to receive at least one minimal value, wherein in case the value of the at least one operating parameter reaches the minimal value, the value of the at least one operating parameter is retained; to provide the control signal to the actuator; and to terminate a weaning process when the value of the at least one operating parameter reaches the minimal value.

12. A device for extracorporeal blood gas exchange, the device comprising: a bloodstream guide area for guiding a bloodstream; a gas-guiding area for guiding a gas stream; a membrane forming a gas-liquid barrier between the bloodstream guided in the bloodstream guide area and the gas stream guided in the gas-guiding area for passing over of carbon dioxide content from the bloodstream into the gas stream; a data network interface; at least one actuator operating based on an actuator operating parameter, which actuator operating parameter has a value that determines a value of the carbon dioxide content which passes over from the bloodstream into the gas stream; and at least one control unit comprising a capnometer and an anesthesia device, the at least one control unit being configured: to receive breathing gas information by means of the data network interface, which breathing gas information indicates a carbon dioxide concentration in a breathing gas; to provide a control signal, which indicates a setting request for setting the value of the operating parameter, to the actuator; to change the value of the operating parameter as a function of the breathing gas information indicative of the carbon dioxide concentration in the breathing gas; to receive at least one minimal value, wherein in case the value of the at least one operating parameter reaches the minimal value, the value of the at least one operating parameter is retained; and to stop a weaning process when the value of the at least one operating parameter reaches the minimal value.

13. A control device for controlling a device for extracorporeal blood gas exchange, wherein the device for extracorporeal blood gas exchange comprises a membrane forming a gas-liquid barrier between a bloodstream and a gas stream, providing a passing over of the carbon dioxide content from the bloodstream into the gas stream and the device for extracorporeal blood gas exchange further comprises at least one actuator operating based on an actuator operating parameter, which actuator operating parameter has a value that determines a value of the carbon dioxide content which passes over from the bloodstream into the gas stream, the control device comprising: an anesthesia device; a capnometer; a fluid inlet for receiving a breathing gas; a measuring unit for determining breathing gas information, which breathing gas information indicates a carbon dioxide concentration in the breathing gas; and at least one control unit configured to: provide a control signal, which indicates a request for setting the value of the actuator operating parameter, as a function of the carbon dioxide concentration in the breathing gas; receive at least one minimal value, wherein in case the value of the at least one operating parameter reaches the minimal value, the value of the at least one operating parameter is retained; and stop a weaning process when the value of the at least one operating parameter reaches the minimal value.

14. A control device in accordance with claim 13, further comprising a data network interface, wherein the control unit is further configured to provide the control signal in the form of a data signal to the data network interface.

15. A control device for controlling a device for extracorporeal blood gas exchange, wherein the device for extracorporeal blood gas exchange comprises a membrane forming a gas-liquid barrier between a bloodstream and a gas stream, providing a passing over of the carbon dioxide content from the bloodstream into the gas stream and the device for extracorporeal blood gas exchange further comprises at least one actuator operating based on an actuator operating parameter, which actuator operating parameter has a value that determines a value of the carbon dioxide content which passes over from the bloodstream into the gas stream, the control device comprising: an anesthesia device; a capnometer; a data network interface configured to receive a data signal, which data signal has breathing gas information, which indicates a carbon dioxide concentration in a breathing gas; and at least one control unit configured to provide a control signal, which indicates a request for setting the value of the actuator operating parameter, as a function of the carbon dioxide concentration in the breathing gas, wherein the at least one control unit receives at least one minimal value as input, wherein in case the value of the at least one operating parameter reaches the minimal value, the value of the at least one operating parameter is retained, wherein the control signal is provided in the form of a data signal to the data network interface, wherein the at least one control unit is further configured to stop a weaning process when the value of the at least one operating parameter reaches the minimal value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic view of a preferred embodiment of a device for extracorporeal blood gas exchange;

(3) FIG. 2 is a flow chart of steps of the method according to the present invention;

(4) FIG. 3 is a flow chart of a preferred embodiment of the method according to the present invention;

(5) FIG. 4 is a flow chart of possible additional steps for carrying out the method according to the present invention in a preferred embodiment;

(6) FIG. 5a is a schematic view showing an interaction of the device for extracorporeal blood gas exchange according to the present invention with an embodiment of a control device for controlling the device for extracorporeal blood gas exchange;

(7) FIG. 5b is a schematic view showing an interaction of the device for extracorporeal blood gas exchange according to the present invention with another embodiment of a control device for controlling the device for extracorporeal blood gas exchange; and

(8) FIG. 6 is a schematic view showing a preferred embodiment of a control device for controlling a device for extracorporeal blood gas exchange over a data network.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) Referring to the drawings, the present invention being described herein takes up the following considerations: a standard range for an end-tidal carbon dioxide concentration (etCO.sub.2) in a breathing gas of a healthy patient is about 5 vol. % (4.5-6 vol. %). Converted into units of pressure at 1,013 hPa, this results in ˜35-45 mmHG as CO.sub.2 partial pressure. The ambient air pressure (1 vol. %=7 mmHG; 1 mmHG=0.15 vol. %; 1 mmHG=1.333 hPa) is included in such a conversion. The carbon dioxide partial pressure in the end-tidal exhaled gas (etCO.sub.2) is about 3-5 mmHG lower than the arterial CO.sub.2 partial pressure of ˜45 mmHG in the blood (paCO.sub.2). The alveolar CO.sub.2 partial pressure (pACO.sub.2) is between the paCO.sub.2 and etCO.sub.2. In case of rebreathing of exhaled breathing gas or due to “shallow breathing” (hypoventilation), the etCO.sub.2 concentration in the breathing gas increases. When less CO.sub.2 can be exhaled due to hyperventilation or lung diseases, e.g., obstruction or COPD, the etCO.sub.2 concentration in the breathing gas drops.

(10) This means that after a reduction in removal of carbon dioxide from the blood by means of a device for extracorporeal blood gas exchange from a previously stable overall situation, the carbon dioxide concentration in the breathing gas drops, if the lung or the lung capacity of the patient has not yet recovered sufficiently. If this is the case, the removal of carbon dioxide from the blood by the device for extracorporeal blood gas exchange must be increased again.

(11) In case the carbon dioxide concentration in the breathing gas does not change considerably after a reduction in the removal of carbon dioxide from the blood by the device for extracorporeal blood gas exchange from a previously stable overall situation, then it can be inferred that the lung or the lung capacity of the patient has recovered to a certain extent, so that the reduction in the removal of carbon dioxide from the blood by the device for extracorporeal blood gas exchange can be retained.

(12) FIG. 1 shows a device V for extracorporeal blood gas exchange. A bloodstream BS is guided via a blood inlet EB along a membrane M and then removed again via a blood outlet AB. The device V preferably has an actuator AK in the form of a pump P, which influences the flow rate of the bloodstream BS along the membrane M.

(13) The bloodstream is thus guided in a bloodstream area BB along the membrane M.

(14) The membrane M separates the bloodstream BS or the bloodstream area BB from a gas stream GS or a gas-guiding area GB.

(15) The gas stream GS is guided from a gas inlet EG along the membrane M to a gas outlet GA.

(16) A quantity of oxygen which is fed to the gas stream GS is controlled via an oxygen source SQ. The oxygen source SQ can preferably be regarded as an actuator AK. The oxygen source SQ has a device component as actuator AK in the form of a valve VT in order to influence the quantity of oxygen of the gas stream GS.

(17) A control unit SE preferably provides a control signal ST1 to the pump P as actuator AK in order to influence the pumping capacity of the pump P.

(18) The control unit SE preferably provides a control signal ST2 to the oxygen source SQ or to the valve VT in order to influence the quantity of oxygen to the gas stream GS.

(19) A certain carbon dioxide content K passes over from the bloodstream BS into the gas stream GS at the membrane. Likewise, oxygen S passes over from the gas stream GS into the bloodstream BS to a certain extent.

(20) If the flow rate of the bloodstream BS is increased by a change in the pumping capacity of the pump P, then the extent at which the carbon dioxide content K passes over from the bloodstream BS into the gas stream GS per unit of time is also increased.

(21) If the oxygen quantity of the gas stream GS is increased, then the extent at which oxygen S passes over from the gas stream GS into the bloodstream BS per unit of time is also increased, wherein the extent at which carbon dioxide K passes over from the bloodstream through the membrane into the gas stream GS is then also increased because of the equilibrium states of the oxygen and carbon dioxide partial pressures at the membrane.

(22) Thus, it is possible to influence at what extent carbon dioxide K passes over from the bloodstream BS into the gas stream GS on the one hand, due to an action of the control unit SE on the oxygen source SQ or on the valve VT by means of the control signal ST2 as well as, on the other hand, due to an action of the control unit SE on the pump P by means of the control signal ST1.

(23) The device V further has a data interface D, via which the data interface D can receive one or more data signals DS.

(24) In a first preferred embodiment, a control signal ST is received by means of the data signal DS at the data network interface D, wherein the control signal ST indicates a request to set a value of an operating parameter of an actuator AK. A change in a value of such an operating parameter brings about a change in the value of the carbon dioxide content K which passes over from the bloodstream BS into the gas stream GS.

(25) In a first preferred embodiment, the control unit SE is configured to provide the control signal ST at one or more of the actuators AK, SQ, VT, P. In case the device V thus preferably has a pump P as actuator AK, the control unit SE selects the control signal ST1 on the basis of the control signal ST received via the data network interface D. Likewise, the control unit SE preferably selects the control signal ST2 to control the valve VT or the oxygen source SQ on the basis of the control signal ST.

(26) As a result, it is thus made possible that the device V for extracorporeal blood gas exchange can be checked or controlled via the data network interface D with respect to the extent at which carbon dioxide passes over from the bloodstream BS into the gas stream GS.

(27) According to a preferred embodiment, the device V receives breathing gas information AI in the form of the data signal DS via the data network interface D, wherein the breathing gas information AI indicates a carbon dioxide concentration in a breathing gas. The control unit SE then provides a control signal ST1 and/or ST2 to at least one actuator AK, wherein the control unit SE selects the value of the operating parameter, which is requested in the control signal, as a function of the carbon dioxide concentration, which is indicated in the breathing gas information AI.

(28) It is consequently possible, on the one hand, that the device V is controlled via the data network interface D by means of receiving the signal ST in the form of the data signal DS by a different unit in the data network. As an alternative, it is possible that the device V receives the breathing gas information AI, which indicates the carbon dioxide concentration in the breathing gas, and then itself selects the corresponding control signals ST1, ST2 as a function of this indicated carbon dioxide concentration in the breathing gas.

(29) For this, preferred interactions or preferred forms of interaction of a device for extracorporeal blood gas exchange with corresponding control devices are shown in FIGS. 5a and 5b.

(30) According to FIG. 5a, the patient PT is ventilated by a ventilator or anesthesia device BG via a ventilation tube, which leads to the patient PT by means of a Y-piece Y via an inspiratory port IP and an expiratory port EP. A sample gas line PG, which picks up a sample gas quantity at the Y-piece Y, leads to a fluid inlet FE of the ventilator or anesthesia device BG.

(31) The patient is further connected to the device V for extracorporeal blood gas exchange via bloodstream lines BSL as explained above by means of venous and/or arterial accesses.

(32) A measuring unit ME is configured to determine a carbon dioxide concentration in the breathing gas by analyzing the gas sample from the sample gas line PG. The device BG further has a control unit SEB as well as preferably a data network interface D for the exchange of data signals DS. The measuring unit ME, the control unit SEB as well as the data network interface D are preferably connected to one another via an internal data bus ID.

(33) The ventilator or anesthesia device BG may in this case be configured as a control device to control a device V for extracorporeal blood gas exchange. The control unit SEB of the ventilator BG may hereby provide a corresponding control signal ST in the form of a data signal DS to the device V.

(34) The device V may then use the data signal DS or control signal ST received via the data interface D by means of its control unit SE in order to actuate an actuator AK correspondingly. The data interface D, the control unit SE as well as the actuator AK are preferably connected to one another by an internal data bus ID.

(35) In case the ventilator BG itself is the control device for controlling the device V for extracorporeal blood gas exchange, the control unit SEB provides the control signal ST as a function of the carbon dioxide concentration in the breathing gas measured by the measuring unit ME. In case the device for extracorporeal blood gas exchange V itself performs the control, the measuring unit ME measures a carbon dioxide concentration in the breathing gas and the device BG transmits breathing gas information AI in the form of a data signal DS to the device V. These two cases correspond to the explanations in reference to FIG. 1 with respect to the control signal ST and the breathing gas information AI.

(36) FIG. 5b shows an alternative embodiment of a control device for controlling a device V for extracorporeal blood gas exchange in the form of a so-called patient monitor PM. The patient monitor PM may, as an alternative, be a so-called capnometer. In this case, the patient monitor PM differs from the ventilator or anesthesia device BG from FIG. 5a in that the patient monitor PM itself does not perform the ventilation of the patient PT from FIG. 5a. However, the patient monitor PM has a fluid inlet FE for connection to a sample gas line PG. By means of a measuring unit ME, the patient monitor PM then measures the carbon dioxide concentration in the breathing gas, which is brought to the fluid inlet via the sample gas line.

(37) The patient monitor PM as a control device for controlling a device V for extracorporeal blood gas exchange may then select a control signal ST and provide it in the form of a data signal DS, as explained above in reference to FIG. 5a with respect to the ventilator or anesthesia device BG. In case the device for extracorporeal blood gas exchange V itself performs the control, the measuring unit ME measures a carbon dioxide concentration in the breathing gas and the patient monitor PM transmits breathing gas information AI in the form of a data signal DS to the device V. These two cases correspond to the explanations in reference to FIG. 1 with respect to the control signal ST and the breathing gas information AI.

(38) FIG. 6 shows another preferred embodiment of a control device DNV for controlling the device V for extracorporeal blood gas exchange.

(39) The control device DNV has a data network interface D, via which the control device DNV exchanges data signals DS via a data network DN with the device V for extracorporeal blood gas exchange as well as a device BG, PM for providing breathing gas information, which indicates a carbon dioxide concentration in a breathing gas.

(40) The control device DNV may thus receive via the data network interface D a data signal DS, which indicates a carbon dioxide concentration in a breathing gas. Such a data signal DS or such breathing gas information may be provided, for example, by a ventilator or anesthesia device BG or by a patient monitor PM, which were described above in reference to FIGS. 5a and 5b, and may be transmitted in the form of data signals DS to the control device DNV.

(41) The control device DNV has a control unit SED, which provides a control signal ST in the form of a data signal DS to the data network interface. Such a data signal DS may then contain or indicate a corresponding control signal ST.

(42) The control unit SED then selects the control signal ST as a function of the indicated carbon dioxide concentration in the breathing gas.

(43) FIG. 2 shows the steps of the method according to the present invention. The method according to the present invention may preferably be carried out on the device V according to the present invention of FIG. 1. The method according to the present invention of FIG. 2 may preferably be implemented by a control device BG, PM, DNV of FIGS. 5a, 5b or FIG. 6 carrying out the method according to the present invention.

(44) The method according to the present invention begins in a start situation of a step 1. Breathing gas information AI, which indicates a carbon dioxide concentration in a breathing gas, is provided in a step 2. In the example of the device V of FIG. 1, this takes place via a corresponding data signal DS. This takes place as an internal providing of a measured value of the corresponding measuring unit ME to the corresponding control unit SEB in the example of the devices BG, PM as control device of FIGS. 5a as well as 5b. In the example of the device DNV as control device, this takes place via a corresponding data signal DS.

(45) A value for an operating parameter is determined in a step 3, wherein this takes place as a function of the carbon dioxide concentration in the breathing gas.

(46) A control signal ST is outputted in a step 4. In the example of the device V of FIG. 1, this is an output of a control signal ST1 and/or ST2 to one or more actuators AK. In the example of the control devices BG, PM of FIG. 5a as well as 5b, this may take place in the form of data signals DS, which have or indicate the corresponding control signal ST. In the example of FIG. 6, the control device DNV may provide the control signal ST as a data signal DS to the device V.

(47) FIG. 3 shows a preferred embodiment of the method according to the present invention.

(48) After the starting step 1, a provided minimal value MF is preferably received in a next step 1A. A plurality of minimal values MF, MOK, which refer to corresponding operating parameters, are preferably provided.

(49) Further, a provided comparison concentration or a comparison value VK is provided or received.

(50) The provided breathing gas information AI is then received in step 2.

(51) A comparison of the carbon dioxide concentration with the comparison value VK is carried out in step 3A. A change in values of the operating parameter is then carried out as a function of a result of this comparison.

(52) If the carbon dioxide concentration is above the comparison value VK, then the process is branched off to a step 3C, in which a value of the operating parameter is changed such that the value of the carbon dioxide content, which passes over from the bloodstream into the gas stream, is reduced. A flow rate F, which can be performed by a pump P of FIG. 1, is preferably reduced by a predefined threshold value F. In addition or as an alternative, an oxygen quantity OK, which is guided to the gas stream GS of FIG. 1, is reduced by the threshold value OK.

(53) The above-mentioned control signal, which may be one of the control signals ST, ST1, ST2, is then outputted in a step 4B.

(54) It is then checked in a step 5A whether the value F of the operating parameter has reached the minimal value MF. If this is not the case, then the process is branched off back to step 2.

(55) If this is the case, then step 5B can preferably be carried out, which, however, is not mandatory.

(56) The process could, in principle, be branched off from step 5A directly to step 6, which ends the method, so that the value of the operating parameter F is then retained.

(57) The value OK of the operating parameter is preferably checked in step 5B to the effect whether this value has reached a corresponding minimal value MOK.

(58) Only if this is the case, the process is actually branched off to step 6, in which the operating parameter is then also left unchanged or the operating parameters are left unchanged.

(59) If it should be determined in step 5B that the corresponding operating parameter OK has not yet reached the corresponding minimal value MOK, then the process is branched off back to step 2.

(60) An embodiment of the method outlined here may be that only the operating parameter F as an influence of the pumping capacity of the pump P of FIG. 1 is changed. In this case, the operating parameter may preferably be left unchanged in relation to the oxygen content of the gas stream. This may then be the case if the device V has a pump P.

(61) In case of a so-called pECLA device, only the quantity of oxygen OK is preferably changed as an operating parameter, because then no pump P of the device V of FIG. 1 is present as actuator AK.

(62) If it was determined in step 3A that the carbon dioxide concentration is above the comparison value VK, then the process can be branched off to a step 3B, in which one or both of the operating parameters F, OK as pumping capacity of the pump or as oxygen quantity of the gas stream are changed such that the extent at which carbon dioxide passes over from the bloodstream into the gas stream, is increased. This preferably takes place only if the carbon dioxide concentration is below another comparison value VK2.

(63) A step 4A, in which a corresponding control signal ST, ST1, ST2 is outputted, takes place in turn in step 3B.

(64) The process is then branched off back to step 2 of the method.

(65) It is possible that in step 2 the breathing gas information AI is a so-called end-tidal carbon dioxide concentration. Such a carbon dioxide concentration is then preferably averaged over time in step 2, so that step 2 lasts a certain period of time.

(66) The breathing gas information AI is preferably already a carbon dioxide concentration measured value averaged over time.

(67) It is not necessary that the carbon dioxide concentration be absolutely an end-tidal concentration. Other carbon dioxide concentrations of a breathing gas are also conceivable.

(68) FIG. 4 shows other steps preferably to be carried out according to a preferred embodiment of the method according to the present invention.

(69) From the steps of the embodiment of the method of FIG. 3, first step 2 is once again shown here, in which the breathing gas information AI is received.

(70) Other steps, which replace step 6 of FIG. 3, then follow the later following step 5A as well as step 5B, which preferably takes place.

(71) A ventilation threshold value BESW as well as at least one piece of information BZ, which indicates an extent for a ventilating state of a lung, are provided and received in a step 7. Such information, which indicates an extent for a ventilating state, may be provided by an electrical impedance tomography (EIT) device. A comparison of the extent for the ventilating state and the ventilation threshold value is then carried out. Whether the value of the at least one operating parameter is retained is made dependent on this. If it appears by this comparison that the ventilating state of the lung is fine, then the process is branched off further downwards, so that the method for changing the value of the operating parameter as a function of the carbon dioxide concentration is finally ended in step 9.

(72) If the comparison of the result is that the ventilating state of the lung is not fine, then the process is branched off back to step 2.

(73) An indicator of a ventilating state of a lung may be the so-called index value RVD as an indicator of a ventilation of the lung. The RVD index is an indicator of regional ventilation delays, as is also known from the documents DE 10 2015 006 902 B3 (corresponding U.S. publication US 2016/0354007 is hereby incorporated by reference in its entirety), or ‘Thomas Muders et al. “Tidal recruitment assessed by electrical impedance tomography and computed tomography in a porcine model of lung injury”.’

(74) According to the Muders study, the RVD index quantifies a delay time of individual lung regions during inhalation, which delay time is standardized to a global inflow period. An impedance value of 40% of the maximum amplitude in the respective—global or regional—course of the impedance curve over the entire duration of inhalation is always selected here as amplitude criterion. RVD values, which can be represented as an RVD map, are then obtained for a plurality of lung regions. An inhomogeneity of the ventilation of lung regions can then be assessed by means of averaging and standard deviation of the RVD values over all individual lung regions. A high regional RVD index is characteristic of pronounced disturbances in the ventilation of the regions of the lung, i.e., a high averaged RVD index characterizes a nonuniform lung ventilation.

(75) Since EIT does not detect absolute impedance changes but rather relative impedance changes and makes an assessment for representing the ventilation situation, there is no uniform standard range for the RVD index. In addition, a 10% threshold value is used instead of the above-mentioned 40% threshold value of the impedance curve in other studies. The following relative RVD criterion, for example, may be applied as an indicator of “recovery” of the lung during the weaning: The RVD index has increased by less than 5-10% after the weaning step has been carried out since the last EIT data collection.

(76) The information BZ is thus preferably information, which indicates measured values RVD1 or RVD2 of different times. In case a percentage change in the measured values falls below the ventilation threshold value BESW, it can be inferred that the ventilating state of the lung is fine
|RVD1−RVD2|/RVD2<BESW
with preferably BESW from a value range of 5% to 10%.

(77) Another indicator of a ventilating state of a lung—or other measured values—may be an indicator of a ratio of ventilation and perfusion V/Q. Such an indicator is known from the documents DE 102014009439 A1 (corresponding U.S. Pat. No. 9,384,549 is hereby incorporated by reference) or EP 1292224 (corresponding U.S. Pat. No. 7,435,226 is hereby incorporated by reference).

(78) A blood exchange in the lung of 5 L/min and a breathing gas exchange of 4 L/min, i.e., a V/Q value of 0.8, are obtained for an average healthy person.

(79) Assuming that the ventilation remains unchanged at the ventilator, a relative V/Q criterion may be applied as an indicator of “recovery” of the lung during the weaning Both an improvement in the perfusion and an improvement in the ventilation are expected as the effects of recovery.

(80) Depending on the clinical picture, a patient with reduced perfusion or with reduced ventilation may be present, which can be detected, e.g., on the basis of the V/Q index.

(81) When the V/Q index has changed by less than +5% for consecutive measurement times, it can then be inferred that the comparison of the information BZ with the weaning step at least does not cause any negative change.

(82) The information BZ is thus preferably information, which indicates measured values VQ1 and VQ2 of different times. In case a percentage change in the measured values falls below the ventilation threshold value BESW, it can be inferred that the ventilating state of the lung is fine
|VQ1−VQ2|/VQ2<BESW
with preferably BESW=5%.

(83) Another indicator of a ventilating state in the lung may be an indicator of a lung outer contour. This is also known from the document DE 10 2014 018 107 A1 (corresponding U.S. Publication 2016/0163062 A1 is incorporated herein by reference in its entirety).

(84) An enlargement of the active, maximum lung area in the dorsal view that can be ventilated with the mechanical ventilation of the lung can be used as an indicator of “recovery” of the lung during the weaning. The lung area available for the gas exchange along a horizontal sectional plane is, in this case, to be viewed synonymously for an overall surface of all alveoli. For example, an enlargement of the lung outer contour, especially of the circumference of the lung, can be used as an indicator of the enlargement of the lung area available for the ventilation.

(85) Since the thoracic circumferences of different people and thus the maximum space that the lung can occupy therein are highly individual and different depending on height, age, gender, body weight, there are no standard ranges for thoracic circumferences or maximum lung outer contours.

(86) Thus, the relative change in circumference, for example, as a relative criterion may be used as an indicator of “recovery” of the lung during the weaning:

(87) The circumference of the determined maximum lung outer contour has increased by more than 5-10% after the weaning step has been carried out since the last EIT data collection or the determined circumference has been changed/reduced at least not considerably (e.g., +5%).

(88) The information BZ is thus preferably information which indicates measured values for a lung outer contour LA1 or LA2 at different times. In case a percentage change in the measured values may fall below the ventilation threshold value BESW, it can be inferred that the ventilating state of the lung is fine
|LA1−LA2|/LA2<BESW
with preferably BESW=5% . . . 10%.

(89) The information BZ as well as the threshold value BESW may be received via a data interface D, for example, the data interface D of the device V of FIG. 1, the data interface D of the device BG of FIG. 5a, the data interface D of the device PM of FIG. 5b or the data interface D of the device DNV of FIG. 6. Such information BZ is usually provided by an EIT device in the form of a data signal. In case the threshold value BESW is not provided via a data signal DS, the threshold value BESW may also be provided on an internal memory of one of the devices V of FIG. 1, BG of FIG. 6a, PM of FIG. 5b or DNV of FIG. 6. Such a memory unit is not shown explicitly in the figures here.

(90) Information IMA, which indicates an indicator of an inspiratory muscle activity, is provided and received in a step 8. This is preferably carried out via a data signal, wherein this data signal can be received in a similar manner at various devices, as explained above in reference to the information BZ.

(91) Furthermore, an activity threshold value ASW is provided and received, wherein this provision or receiving may take place in a manner similar to the threshold value BESW.

(92) The retaining of the value of the operating parameter is further made dependent on a comparison of the indicator of the inspiratory muscle activity and the activity threshold ASW to the effect that in case the inspiratory muscle activity is sufficiently high, the process is then branched off to step 9, in which the value of the operating parameter is then retained or left unchanged.

(93) If the comparison of the indicator of the inspiratory muscle activity with the activity threshold value is not satisfactory, the process is then branched off back to step 2 of the method.

(94) An indicator of an inspiratory muscle activity may be provided by an external device, for example, a device for determining muscle activity signals on the basis of sensor signals of electromyographic sensors. Methods for determining signals of inspiratory muscle activity are known from German Patent Application No. 102015015296.3. An indicator of an inspiratory muscle activity may in this case be an energy of such a processed sensor signal, which can then be compared with a minimal value for a signal energy as the activity threshold value. As a result, it can be detected whether the possibility for spontaneous breathing by the patient is already present such that he can sufficiently breathe independently.

(95) Finally, as explained above in reference to FIG. 3 with respect to step 6, the at least one operating parameter is then left unchanged in step 9. In this connection, an output signal ASG1 is preferably outputted as information about the fact that the operating parameter, for example, the pumping capacity of the pump or else the oxygen quantity of the oxygen source, has reached a corresponding minimal value.

(96) A blood gas measured value BG1, which corresponds to a first measurement time, is then received or provided in another step 10.

(97) One then preferably waits in a step 11 for a predefined time T.

(98) A second blood gas measured value BG2, which corresponds to a second measurement time, is received or provided at a later, second time.

(99) A comparison of the blood gas measured values BG1, BG2 is then carried out in a step 13, taking a provided blood gas threshold value BSW into consideration.

(100) For a patient, in whom the removal of carbon dioxide from the blood via his own lung capacity or lung is sufficient, it can then be inferred from values of a blood gas measurement at different times that the patient is maintaining a sufficiently stable condition or that his own lung capacity is sufficient for the removal of carbon dioxide from the blood.

(101) In case an analysis of the blood gas measured value BG1, BG2 as well as the blood threshold value BSW indicates a sufficient recovery of the breathing organs, the process may then be branched off to a step 20, in which the method is finally ended. An output signal ASG2 may then be outputted in step 20, which output signal informs a clinician about the fact that the analysis of the blood gas measured values BG1, BG2 was satisfactory.

(102) Depending on the type of blood gas threshold value, the analysis of the blood gas measured values BG1, BG2 as well as of the blood threshold value BSW is preferably satisfactory if the blood gas measured values BG1, BG2 both fall below the blood threshold value BSW
BG1,BG2<BSW.

(103) Depending on the type of blood gas measured value, the analysis of the blood gas measured value BG1, BG2 as well as of the blood threshold value BSW may preferably also be satisfactory, however, if the blood gas threshold values BG1, BG2 both exceed the blood threshold value BSW
BG1,BG2>BSW.

(104) The analysis of the blood gas measured values BG1, BG2 as well as of the blood threshold value BSW2 is preferably satisfactory if, as an alternative or in addition, a difference in quantity in the blood gas measured values BG1, BG2 falls below the other blood threshold value BSW2
|BG1−BG2|<BSW2,
because then a change in the blood gas value over time is sufficiently minor.

(105) A type of blood gas value may be, for example: a carbon dioxide partial pressure of the blood pCO.sub.2, an oxygen partial pressure of the blood pO.sub.2, or a pH value of the blood.

(106) A corresponding, individual threshold value BSW and/or BSW2 can then be selected or predefined for a corresponding blood gas value.

(107) The carbon dioxide partial pressure in the blood pCO.sub.2 as a type of blood gas measured value is, for example, within a normal range of 40 mmHG, preferably 36 mmHG to 44 mmHG in healthy adults. The carbon dioxide partial pressure in the blood pCO.sub.2 is increased when the overall removal of carbon dioxide from the blood by means of breathing and extracorporeal blood gas exchange is not sufficient during weaning A sufficiently recovered breathing of a patient lowers the carbon dioxide partial pressure in the blood. The threshold value BSW related to the carbon dioxide partial pressure in the blood is selected to be, e.g., 44 mmHG, wherein the blood gas values BG1, BG2 have to be lower than the threshold value BSW. The threshold value BSW2 related to the difference in quantity of the carbon dioxide partial pressure measured values in the blood is selected to be, e.g., 1 mmHG to 3 mmHG.

(108) A pH value as a type of blood gas measured value is, e.g., in a standard range for values of 7.35 to 7.45 for adults. If values of 0<7.35 are present, then this is called hyperacidification or acidosis. If values of 7.45 to 14 are present, then this is called hypoacidification or alkalosis. The pH value is especially connected to an increase in the carbon dioxide partial pressure in the blood in case of a respiratory disturbance. Carbon dioxide dissolved in the blood is an acid (carbonic acid), i.e., when the carbon dioxide value in the blood is increased, the pH value is, for example, lower than 7.32. The blood gas values BG1, BG2 have to be lower than a threshold value BSW of, e.g., 7.32. The threshold value BSW2 related to the difference in quantity of the pH measured values in the blood is selected to be, e.g., 0.1 to 0.3.

(109) The oxygen partial pressure pO.sub.2 as a type of blood gas measured value is, e.g., in a normal range for values of 75-97 mmHG for adults. The blood gas values BG1, BG2 must be lower than a threshold value BSW of, e.g., 75 mmHG. The threshold value BSW2 related to the difference in quantity of the oxygen partial pressure measured values BG1, BG2 is selected here to be, e.g., 5 mmHG to 7 mmHG.

(110) Further, a base excess (BE) value may be used as a type of blood gas measured value, which base excess value makes it possible to assess the metabolism or the non-breathing-related portions of disturbances of the metabolism in the acid-base balance. It the acid-base balance is assessed in connection with the pCO.sub.2 partial pressure in order to confirm a diagnosis of respiratory acidosis, for example. Since the BE value within the framework of a blood gas analysis is often also determined anyway, the BE value can be used in addition to the pCO.sub.2 partial pressure in certain situations and in a patient-type-specific manner (e.g., clinical pictures with base loss in case of intensified loss of fluid (diarrhea)) in order to suspend the weaning, for example, in such a situation (diarrhea) or the ending of the weaning with disconnection from the device for extracorporeal blood gas exchange until this situation (diarrhea) has improved.

(111) The output signals ASG1, ASG2 may be output signals for actuating an optical and/or acoustic output unit. Further, the output signals ASG1, ASG2 may be such that these output signals are provided in the form of data signals to data network interfaces at other network units in order to then be used there for an actuation of optical and/or acoustic output units.

(112) If a comparison of the blood gas measured value of the threshold value BSW is not satisfactory, then the process is branched off back to a step 14, in which an output signal ASG3 is outputted, which indicates a warning. This output signal ASG3 may also be provided in a different form, as already explained above in reference to the output signals ASG1, ASG2.

(113) The blood gas values BG1, BG2 are thus taken into consideration such that after completion of the method for changing the value of the operating parameter, it is possible to verify whether a capacity of the lung for gas exchange is present to a sufficient extent, and thus ending of the extracorporeal lung assistance may now be carried out. In this connection, blood gas values may emerge from a blood gas analysis.

(114) A step 15 then follows, in which one waits for an input of an input signal EGS by an input unit. As a result, a clinician is enabled to let the method for changing the value of the operating parameter restart due to the input of the input signal EGS, so that the process is then branched off back to step 2.

(115) According to the proposed method, an operating parameter, for example, a pumping capacity F or oxygen quantity OK, is reduced according to a predefined increment F or OK in an embodiment from FIG. 3. These increments may be selected depending on the patient. This may take place, for example, by a receiving of corresponding increment values via the data interface D in the form of data signals DS, see FIG. 1. Likewise, in case the devices BG of FIG. 5a, PM of FIG. 5b or DNV of FIG. 6 are the devices carrying out the method, the increment values F, OK may be received as data signals DS. Such values in the form of data signals DS may be predefined, for example, by a central IT system of a clinical setting. As an alternative, it is possible that the device V of FIG. 1, the device BG of FIG. 5a, the device PM of FIG. 5b or the device DNV of FIG. 6 receive data, for example, age, height, body weight or past medical history as well as current clinical picture as additional information in the form of data signals DS from a patient data management system and then correspondingly selects the increment values F, OK on the basis of these data signals or the content thereof.

(116) The statements made above for the increment values F, OK may also apply to one or more of the following values: comparison values VK, VK2 minimal values MF, MOK, ventilation threshold value BESW, activity threshold value ASW, blood gas threshold values BSW, BSW2.

(117) Even though some aspects were described in connection with a device or a plurality of devices, it is understood that these aspects also represent a description of the corresponding method, so that a block or a component of a device is also defined as a corresponding method step or as a feature of a method step. Similarly, aspects, which were described in connection with a method step or as a method step, also represent a description of a corresponding block or detail or feature of a corresponding device.

(118) Depending on certain implementation requirements, exemplary embodiments of the present invention may be implemented in hardware and/or in software. A control unit may likewise be implemented in hardware or in software. The implementation may be carried out with the use of a digital storage medium, for example, a floppy disk, a DVD, a Blu-Ray disk, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, a hard drive or another magnetic or optical memory, on which electronically readable control signals, which can interact or do interact with a programmable hardware component such that the respective method is carried out, are stored.

(119) A programmable hardware component may be formed by a processor, a computer processor (CPU=Central Processing Unit), a graphics processor (GPU=Graphics Processing Unit), a computer, computer system, an application-specific integrated circuit (ASIC=Application-Specific Integrated Circuit), a single-chip system (SOC=System on Chip), a programmable logic element field-programmable gate array with a microprocessor (FPGA=Field Programmable Gate Array).

(120) The digital storage medium may therefore be machine- or computer-readable. Some exemplary embodiments consequently comprise a data storage medium, which has electronically readable control signals, which are capable of interacting with a programmable computer system or with a programmable hardware component such that one of the methods being described here is executed. An exemplary embodiment is thus a data storage medium (or a digital storage medium or a computer-readable medium), on which the program is recorded for executing a method being described here.

(121) Exemplary embodiments of the present invention may generally be implemented as a program, firmware, computer program or computer program product with a program code or as data, wherein the program code or the data acts/act such as to execute one of the methods when the program is running on a processor or on a programmable hardware component. The program code or the data may also be stored on a machine-readable storage medium or data storage medium. The program code or the data may be present, among other things, as a source code, machine code or byte code as well as another intermediate code.

(122) Further, another exemplary embodiment is a data stream, a signal sequence or a sequence of signals, which represents/represent the program for executing one of the methods being described here. The data stream, the signal sequence or the sequence of signals may be configured, for example, such as to be transferred via data communication connection, for example, via the internet or another network. Exemplary embodiments are thus also signal sequences, which represent data and which are suitable for transmission via a network or a data communication connection, wherein the data represent the program.

(123) A program according to one exemplary embodiment may implement one of the methods during its execution, for example, by reading storage locations or writing a datum or a plurality of data into these, as a result of which switching operations or other procedures are brought about in transistor structures, in amplifier structures or in other electrical, optical, magnetic components or components operating according to another principle of operation. Data, values, sensor values or other information may correspondingly be detected, determined or measured by a program by reading a storage location. A program may therefore detect, determine or measure variables, values, measured variables and other information by reading one or more storage locations as well as bring about, prompt or execute an action by writing to one or more storage locations as well as actuate other devices, machines and components.

(124) The above-described exemplary embodiments represent only an illustration of the principles of the present invention. It is obvious that modifications and variations of the arrangements and details being described here will be seen by other persons skilled in the art. The present invention is therefore intended to be limited only by the scope of protection of the following patent claims rather than by the specific details that were presented here on the basis of the description and the explanation of the exemplary embodiments. 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.