PROCESS AND DEVICE FOR DETECTION OF A LEAK IN A VENTILATION CIRCUIT

Abstract

A process for monitoring a measuring system (110) for mechanical ventilation of a patient (20) is carried out while a fluid connection (40) is established between the patient (20) and a medical device (100). A gas sample is suctioned from the fluid connection (40) and is sent through a gas sensor fluid-guiding unit (52) to a gas sensor array (50). A time curve of the CO2 concentration and O2 concentration in the suctioned gas sample are determined. A concentration change curve of the change over time of the CO2 concentration and the O2 concentration are calculated. A search is made for a time period in which the two concentration change curves continuously have the same sign. Upon detecting such a time period it is checked whether a predefined first leak criterion is met. When this is the case, an indication of a leak (L) is detected.

Claims

1. A process for monitoring a measuring system for mechanical ventilation of a patient, the process comprising the steps of: providing the measuring system, wherein the measuring system comprises: a gas sensor array and a gas sensor fluid-guiding unit, and wherein the process is performed while a fluid connection, between the patient and a medical device is established, using a patient-side fluid-guiding unit; suctioning a gas sample from the patient fluid-guiding unit and guiding the gas sample through the gas sensor fluid-guiding unit to the gas sensor array, with the fluid connection being established; calculating an indicator of progress over time of a concentration of carbon dioxide, as a carbon dioxide concentration time curve, in the suctioned gas sample and an indicator of progress over time of a concentration of another gas, different from carbon dioxide, with respect to time, as another gas concentration time curve, in the suctioned gas sample using measured values of the gas sensor array; calculating an indicator of progress over time of temporal change of the carbon dioxide concentration, as a carbon dioxide concentration change curve, and an indicator of progress over time of temporal change of the concentration of the other gas, as another concentration change curve, using the carbon dioxide concentration time curve and the other gas concentration time curve; searching for time periods with a same sign, wherein during a same sign time period the two concentration change curves have a same sign throughout the same sign time period, with both greater than zero or both less than zero; checking, upon at least one same sign time period being detected, whether the two concentration change curves meet a predefined first leak criterion in the detected at least one same sign time period; and determining a leak has occurred, between the patient fluid-guiding unit and the gas sensor array or determining there is an indication of such a leak, when the first leak criterion is met.

2. A process in accordance with claim 1, wherein the first leak criterion depends on at least one of the following parameters: a duration of the same sign time period; an entire duration of all same sign time periods detected since a predefined reference time; an arithmetic product of the two values that the two concentration change curves assume at at least one sample time in the same sign time period; an arithmetic sum of a plurality of such arithmetic products of values with the same sign within the same sign time period; and a sum of all such arithmetic products for all sample times within at least one same sign time period.

3. A process in accordance with claim 1, wherein a calculated phase shift of the carbon dioxide concentration change curve in relation to the other concentration change curve is carried out such that after the calculated phase shift a maximum of the carbon dioxide concentration change curve falls on the same time as a maximum or minimum of the other concentration change curve.

4. A process in accordance with claim 1, wherein: each exhalation time period, corresponding to a time period in which the patient exhales air, is detected, and the search for time periods with the same sign is carried out only in the detected exhalation time periods.

5. A process in accordance with claim 1, further comprising carrying the steps of: measuring progress over time of a pressure at a measuring point in or at the gas sensor array or in or at the gas sensor fluid-guiding unit; and calculating an indicator of progress over time of a change of the measured pressure; calculating an indicator of a phase shift between the two concentration curves; calculating an indicator of progress over time of a change of the calculated phase shift indicator; and checking whether a predefined second leak criterion is met, wherein: the second leak criterion depends on the change of the phase shift indicator progress over time and the pressure change progress over time indicator; upon detecting that at least one of the two leak criteria is met, determining that a leak has occurred between the patient fluid-guiding unit and the gas sensor array or determining that there is an indication of such a leak.

6. A process in accordance with claim 5, wherein the second leak criterion depends on: the phase shift change progress over time indicator at a first sample time; and the pressure change progress over time at a second sample time, wherein the time interval between the two sample times depends on the interval between the measuring point, at which the pressure is measured, and a measuring point, at which the two concentrations are being measured.

7. A process in accordance with claim 6, wherein the second leak criterion is met when: the phase shift indicator change progress over time at the first sample time is above a first predefined threshold; and the pressure change progress over time at the second sample time is above a second predefined threshold.

8. A process in accordance with claim 1, wherein: upon detecting that at least one of the first leak criterion and the second leak criterion is met carrying out a check; the check comprises: interrupting the step of suctioning a gas sample from the patient fluid-guiding unit; measuring a pressure in the patient fluid-guiding unit and measuring a pressure at a measuring point in or at the measuring system while the suctioning of the gas sample is interrupted; comparing the two measured pressures; and upon the comparison of the two pressures meeting a predefined third leak criterion determining that a leak has occurred.

9. A measuring system for a mechanical ventilation of a patient, the measuring system comprising: a gas sensor array; a gas sensor fluid-guiding unit connected to or connectable to a patient fluid-guiding unit, wherein a fluid connection is establishable by means of the patient fluid-guiding unit between the patient and a medical device, wherein the measuring system is configured to deliver gas from the patient fluid-guiding unit through the gas sensor fluid-guiding unit to the gas sensor array; and a signal processing unit configured to: calculate an indicator of a concentration of carbon dioxide with respect to time, as a carbon dioxide concentration time curve, in the suctioned gas sample using measured values of the gas sensor array; calculate an indicator of a concentration of another gas, different from carbon dioxide, with respect to time, as another gas concentration time curve, in the suctioned gas sample using measured values of the gas sensor array; calculate an indicator of change over time of temporal change of the carbon dioxide concentration, as a carbon dioxide concentration change curve, using the carbon dioxide concentration time curve; calculate an indicator of a change over time of temporal change of the concentration of the other gas, as another concentration change curve, using the other gas concentration time curve; search for time periods with a same sign, wherein during a same sign time period the two concentration change curves have a same sign throughout the same sign time period, with both greater than zero or both less than zero; upon detecting at least one same sign time period, check whether the two concentration change curves meet a predefined first leak criterion in the detected at least one same sign time period; and upon the first leak criterion being met, determining that a leak has occurred between the patient fluid-guiding unit and the gas sensor array or that there is an indication of such a leak.

10. A connection device for the mechanical ventilation of a patient, the connection device comprising: a patient fluid-guiding unit; and a measuring system comprising: a gas sensor array; a gas sensor fluid-guiding unit connected to or connectable to a patient fluid-guiding unit, wherein a fluid connection is establishable by means of the patient fluid-guiding unit between the patient and a medical device, wherein the measuring system is configured to deliver gas from the patient fluid-guiding unit through the gas sensor fluid-guiding unit to the gas sensor array; and a signal processing unit configured to: calculate an indicator of a concentration of carbon dioxide with respect to time, as a carbon dioxide concentration time curve, in the suctioned gas sample using measured values of the gas sensor array; calculate an indicator of a concentration of another gas, different from carbon dioxide, with respect to time, as another gas concentration time curve, in the suctioned gas sample using measured values of the gas sensor array; calculate an indicator of change over time of temporal change of the carbon dioxide concentration, as a carbon dioxide concentration change curve, using the carbon dioxide concentration time curve; calculate an indicator of a change over time of temporal change of the concentration of the other gas, as another concentration change curve, using the other gas concentration time curve; search for time periods with a same sign, wherein during a same sign time period the two concentration change curves have a same sign throughout the same sign time period, with both greater than zero or both less than zero; upon detecting at least one same sign time period, check whether the two concentration change curves meet a predefined first leak criterion in the detected at least one same sign time period; and upon the first leak criterion being met, determine that a leak has occurred between the patient fluid-guiding unit and the gas sensor array or that there is an indication of such a leak.

11. A medical system comprising: a medical device; and a connection device comprising: a patient fluid-guiding unit; and a measuring system comprising: a gas sensor array; a gas sensor fluid-guiding unit connected to or connectable to a patient fluid-guiding unit, wherein a fluid connection is establishable by means of the patient fluid-guiding unit between the patient and a medical device, wherein the measuring system is configured to deliver gas from the patient fluid-guiding unit through the gas sensor fluid-guiding unit to the gas sensor array; and a signal processing unit configured to: calculate an indicator of a concentration of carbon dioxide with respect to time, as a carbon dioxide concentration time curve, in the suctioned gas sample using measured values of the gas sensor array; calculate an indicator of a concentration of another gas, different from carbon dioxide, with respect to time, as another gas concentration time curve, in the suctioned gas sample using measured values of the gas sensor array; calculate an indicator of change over time of temporal change of the carbon dioxide concentration, as a carbon dioxide concentration change curve, using the carbon dioxide concentration time curve; calculate an indicator of a change over time of temporal change of the concentration of the other gas, as another concentration change curve, using the other gas concentration time curve; search for time periods with a same sign, wherein during a same sign time period the two concentration change curves have a same sign throughout the same sign time period, with both greater than zero or both less than zero; upon detecting at least one same sign time period, check whether the two concentration change curves meet a predefined first leak criterion in the detected at least one same sign time period; and upon the first leak criterion being met, determine that a leak has occurred between the patient fluid-guiding unit and the gas sensor array or that there is an indication of such a leak, wherein the medical device is configured: to receive measured time curves of the carbon dioxide concentration and of the concentration of the other gas from the measuring system of the connection device; and to at least one of process the received time curves and to output the received time curves in a form perceptible by a person.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In the drawings:

[0058] FIG. 1 is a schematic view showing a ventilation circuit for the mechanical ventilation of a patient;

[0059] FIG. 2 is a graph showing the change in CO2 concentration with respect to time (CO2 concentration progress over time—the CO2 concentration time curve) and the change in O2 concentration with respect to time (O2 concentration progress with respect to time—the O2 concentration time curve) during a single breath in the absence of a leak;

[0060] FIG. 3 is a graph showing the time curves of FIG. 2 in the presence of a leak;

[0061] FIG. 4 is a graph showing the scaled time curves of CO2, O2, N2O and anesthetic in the absence and in the presence of a leak;

[0062] FIG. 5a is a graph showing the CO2 concentration progress over time (CO2 concentration time curve) and O2 concentration progress over time (O2 concentration time curve) of FIG. 2 standardized to a range of −1000 to +1000;

[0063] FIG. 5b is a graph showing the CO2 concentration progress over time and O2 concentration progress over time of FIG. 3 standardized to a range of −1000 to +1000;

[0064] FIG. 6a is a graph showing the progress over time of temporal changes of standardized CO2 and O2 concentration (the changes over time of the standardized CO2 and O2 concentration time curves—concentration change curves) of FIG. 5a as well as the progress over time (time curve) of the product values;

[0065] FIG. 6b is a graph showing the progress over time of temporal changes of standardized CO2 and O2 concentration (the changes over time of the standardized CO2 and O2 concentration time curves—concentration change curves) of FIG. 5b as well as the progress over time (time curve) of the product values;

[0066] FIG. 7 is a graph showing consequences of leaks which were generated in a test multiple times and again eliminated, and the detection thereof;

[0067] FIG. 8 is a graph showing the progress over time (time curve) of the CO2 concentration and the progress over time (time curve) of the covariance between CO2 and O2;

[0068] FIG. 9 is a graph showing the progress over time (time curve) of the pressure P.sub.Cell as well as of the signal DiPhaC in case of a ventilation with high rate and low ventilation pressure;

[0069] FIG. 10 is a graph showing, as an example, the progress over time (time curve) of ΔCov[CO2,O2] and progress over time (time curve) ΔP.sub.cell; and

[0070] FIG. 11 is a graph showing the progress over time (time curve) of the signal DPC in the situation of FIG. 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0071] Referring to the drawings, FIG. 1 schematically shows a ventilation circuit 40 to mechanically ventilate a patient 20. It is possible that the ventilation circuit 40 feeds an anesthetic to the patient 20, so that the patient 20 is partly or fully sedated. The present invention can also be used in a ventilation circuit 40, in which the patient 20 is mechanically ventilated, but no anesthetic is fed to the patient 20. It is possible that the mechanical ventilation and the spontaneous breathing of the patient 20 overlap.

[0072] A patient-side coupling unit 21, for example, a mouthpiece or breathing mask, connects the patient 20 to the ventilation circuit 40. The mouthpiece 21 is connected to a Y-piece 22. The Y-piece 22 is connected to a breathing gas line 32 for inhalation (inspiration) and to a breathing gas line 33 for exhalation (expiration).

[0073] The ventilation circuit 40 connects the patient-side coupling unit 21 to the ventilator 100, which is configured as an anesthesia apparatus in one configuration of the exemplary embodiment. The ventilation circuit 40 is passed through the ventilator 100.

[0074] FIG. 1 schematically shows which components described below belong to the ventilator 100 of the exemplary embodiment.

[0075] A delivery unit 24a in the form of a pump or of a blower suctions breathing gas and generates a permanent stream of breathing gas through the inhalation breathing gas line 32 toward the Y-piece 2 and toward the patient 20. This delivery unit 24a preferably operates as a compressor, which generates an overpressure and rotates with a speed of over 10,000 rpm. A carbon dioxide absorber 25a is capable of absorbing carbon dioxide from the ventilation circuit 40. A nonreturn valve 23a lets a gas flow in the inhalation breathing gas line 32 pass to the Y-piece 22 and blocks a gas flow in the reverse direction.

[0076] A nonreturn valve 23b lets a gas flow in the exhalation breathing gas line 33 pass from the Y-piece 22 and blocks a gas flow in the reverse direction. An actuatable PEEP valve 24b (PEEP=“positive end-expiratory pressure”) lets, depending on the position, the air stream, which the delivery unit 24a has generated, to pass or blocks it and as a result generates the individual ventilation strokes and fixes the amplitudes and frequencies of these ventilation strokes. The PEEP valve 24b ensures, in addition, that a sufficiently high air pressure is also maintained in the lungs of the patient 20 at the end of the exhalation or during a brief opening or interruption of the ventilation circuit 40. An overpressure valve 29 is capable of building up an overpressure in the ventilation circuit 40 by breathing gas being released into the surrounding area. This overpressure valve 29 is preferably configured as an “adjustable pressure limiting valve” and reduces the risk that the lungs of the patient 20 are damaged, especially in case of a manual ventilation by means of a breathing bag 26. The pressure limit at which this overpressure valve 29 opens can be adjusted manually from outside and/or automatically by an actuation of the overpressure valve 29.

[0077] An optional anesthetic vaporizer 31 is capable of feeding a fluid stream 28 with a mixture in vapor form of a carrier gas and at least one anesthetic into the ventilation circuit 40. In addition, a fluid stream 27 of fresh air or of another fresh gas can be fed to the ventilation circuit 40.

[0078] The ventilation circuit 40 is kept running by the delivery unit 24a and optionally by a breathing bag 26, which can be actuated manually.

[0079] The delivery unit 24a, the optional anesthetic vaporizer 31, the carbon dioxide absorber 25a, the nonreturn valves 23a and 23b as well as the valves 24a and 29 belong to the schematically shown ventilator 100, which can be configured as an anesthesia apparatus. It is also possible that the ventilation circuit 40 is kept running exclusively by means of the breathing bag 26, for example, onboard a vehicle or at another location, at which no stationary power supply is available, or the power supply has failed, or the delivery unit 24 has broken down.

[0080] A control device 35 receives measured values from a pressure sensor 58, which measures the air pressure P.sub.amb in the surrounding area of the ventilator 100. In addition, the control device 35 receives measured values from a pressure sensor 36, which measures the current pressure in the ventilation circuit 40, for example, the ventilation pressure (airway pressure, P.sub.aw) present at the patient 20, preferably as pressure in relation to the ambient pressure P.sub.amb. The control device 35 actuates the delivery unit 24a, the anesthetic vaporizer 31 and other components of the ventilator 100, in order to achieve a desired ventilation of the patient 20. The control device 35 comprises one or more processors and memory—non-volatile memory and/or volatile memory.

[0081] For the actuation of the ventilator 100, it is necessary that the actual current concentration of carbon dioxide (CO2), oxygen (O2), nitrous oxide (N2O) and optionally a fed-in anesthetic be measured, especially the concentrations close to the patient-side coupling unit 21 and thus close to the mouth and/or close to the nose of the patient 20.

[0082] For this purpose, a sample containing breathing gas is taken (branched off) via a gas sample fluid-guiding unit in the form of a removal hose 52 from the ventilation circuit 40 and fed again into the ventilation circuit 40 via a feed hose 56. The removal hose 52 begins in a branching-off point 34 between the patient-side coupling unit 21 and the Y-piece 22. Optionally, a valve, not shown, that separates the removal hose 52 from the ventilation circuit 40 in the closed position and that can be actuated by the control device 35 is located at the branching-off point 34. When the valve is open, the removal hose 52 is in an unrestricted fluid connection with the ventilation circuit 40. The discharge hose 56 leads to a feed point upstream of the carbon dioxide absorber 25a.

[0083] The removal hose 52 sends the breathing gas sample to a gas sensor array 50. This gas sensor array 50 is located at a distance in space from the patient-side coupling unit 21 and in one embodiment belongs to the ventilator 100. The gas sensor array 50 comprises a pump 55 that suctions breathing gas through the removal hose 52. The pump 55 preferably continuously generates a vacuum on the side pointing toward the removal hose 52 and continuously an overpressure on the side pointing toward the discharge hose 56. The pump 55 is capable of generating a volume flow of, for example, 200 mL/min.

[0084] A sensor 54 is capable of measuring signals that correlate with the respective concentration of CO2, O2 and anesthetic in the suctioned gas sample. This sensor 54 preferably comprises an infrared measuring head, which utilizes the dipole moment of molecules in the breathing gas sample and quantitatively analyzes the absorption of infrared-active gases in order to determine the respective concentration. A sensor 53 is capable of measuring a signal which correlates with the concentration of O2. It is possible that the gas sensor array 50 comprises additional sensors, especially in order to provide redundancy. In addition, the gas sensor array 50 comprises a pressure sensor 57, which measures the pressure P.sub.cell of the breathing gas sample at the inlet of the gas sensor array 50. This pressure P.sub.cell is variable over time, because the pressure in the ventilation circuit 50 varies and because the removal hose 52 is in a fluid connection with the ventilation circuit 40 when no valve is present at the branching-off point 34 or as long as the optional valve at the branching-off point 34 is open, so that the pressure in the ventilation circuit 40 travels approximately at the speed of sound to the gas sensor array 50.

[0085] In one embodiment, the sensors 53 and 54 measure partial pressures, for example, using optical measuring processes. The pressure sensor 57 measures the entire absolute pressure P.sub.cell,abs of the breathing gas sample. The quotient of a partial pressure and the entire absolute pressure P.sub.cell,abs yields an indicator of the concentration of a gas in the suctioned gas sample.

[0086] The pressure sensor 57 preferably measures an absolute pressure P.sub.cell,abs. The internal pressure in the gas sensor array 50 in relation to the ambient pressure P.sub.amb is used as the pressure P.sub.cell below, i.e., P.sub.cell=P.sub.cell,abs−P.sub.amb. The relative pressure P.sub.cell may therefore also have negative values, namely in case of a vacuum in the gas sensor array 50 in relation to the ambient pressure P.sub.amb. The relative pressure is preferably measured multiple times during a breathing process. A value, which was calculated by suitable averaging of these measured values obtained during a breathing process, is used as the pressure P.sub.cell.

[0087] A data-processing signal processing unit 30 receives measured values from the sensors of the gas sensor array 50, especially from the CO2, N2O and anesthetic sensor 54, from the O2 sensor 53, from the pressure sensors 57 and 58 and optionally from additional sensors, and then automatically analyzes these measured values. The data-processing signal processing unit 30 comprises one or more processors and memory—non-volatile memory and/or volatile memory. Depending on the measured values received, the signal processing unit 30 generates signals concerning the respective current concentration of O2, CO2, N2O as well as anesthetic and transmits these signals to the control device 35. The control device 35 uses these received signals to actuate actuators of the ventilator 100 and, as a result, to automatically control the ventilation circuit 40.

[0088] The breathing gas sample that is preferably suctioned continuously by the pump 55 flows through a water trap 51, which is arranged upstream of the sensors 53 and 54. This water trap 51 is equipped with at least one gas-permeable diaphragm, this diaphragm being preferably made of a chemically inert material, e.g., polytetrafluoroethylene (PTFE). This water trap 51 may be configured, for example, as described in DE 10 2007 046 533 B3 (and corresponding U.S. Pat. No. 8,291,903 (B2)) or in DE 10 2009 024 040 A1 (and corresponding U.S. Pat. No. 8,221,530 (B2)). U.S. Pat. No. 8,291,903 (B2) and U.S. Pat. No. 8,221,530 (B2) are incorporated herein by reference. In this way, the suctioned breathing gas sample is freed from condensate, particles, suspended matter and germs. Liquid, especially condensed water vapor, is retained by the diaphragm and flows into a tank of the water trap 51.

[0089] The gas sensor array 50, the water trap 51 and the signal processing unit 30 belong to a measuring system 110, which is schematically shown in FIG. 1.

[0090] It is possible that a leak occurs on the path from the branching-off point 34 of the removal hose 52 up to the sensors 54 and 53, for example, because the removal hose 52 is not connected in a fluid-tight manner to the patient-side coupling unit 21, to the Y-piece 22 or to the water trap 51 or because material fatigue or a mechanical action from outside has led to a leak. This leak may occur abruptly, for example, because the mechanical ventilation has begun, even though two parts are incorrectly connected to one another incorrectly in a non-fluid-tight manner, or gradually, for example, because of material fatigue. A leak L in the transition between the removal hose 52 and the water trap 51 is shown as an example in FIG. 1.

[0091] Such a leak L may distort the measured results of the sensors 53 and 54 and of optional additional sensors. Then in the removal hose 52 a vacuum in relation to the ambient pressure P.sub.amb and also in relation to the pressure P.sub.aw occurs in the ventilation circuit 40 at least during the exhalation. This vacuum results from the fact that the measuring system 110 continuously suctions a breathing gas sample, and is, for example, 100 hPa. Therefore, ambient air can be suctioned through this leak L into the removal hose 52 or into the gas sensor array 50. Because the vacuum in the removal hose 52 varies in relation to the ambient pressure P.sub.amb, the quantity of the ambient air suctioned in also varies over time, as a rule.

[0092] The suctioned-in ambient air may simulate an oxygen concentration in the ventilation circuit 40 that is higher than or also lower than the actual oxygen concentration and hence lead to an incorrect measurement. This incorrect measurement may lead to an error during the mechanical ventilation of the patient 20. Hence, a leak L must be detected as quickly as possible, and a corresponding alarm must be outputted in order to be able to rapidly eliminate the leak L. On the other hand, it is desired to generate as few nuisance alarms as possible, ideally no nuisance alarms at all.

[0093] In case no leak occurs, then the progress over time of the O2 concentration (the O2 concentration with respect to time—O2 concentration time curve) in the ventilation circuit 40 and hence also in the branched-off breathing gas sample is approximately inverted to the progress over time of the CO2 concentration (the CO2 concentration with respect to time—concentration time curve), ideally phase-shifted by half the duration of a breath, in case inhalation and exhalation are of equal duration. During the inhalation, the O2 concentration is markedly higher, and the CO2 concentration is markedly higher, as a rule, during the exhalation. FIG. 2 shows, as an example, the progress over time of the O2 concentration (the O2 concentration with respect to time or O2 concentration time curve) and the progress over time of the CO2 concentration (the CO2 concentration with respect to time or CO2 concentration time curve) during a single breath in a situation, in which no leak has occurred. A scale for time is plotted on the x axis. The sample frequency is thus 50 Hz. The numbers designate the consecutive numbers of the measuring points, wherein the interval between two consecutive measuring points is 20 msec. The left-hand side of the y axis shows a scale for the CO2 concentration in volume %, and the right-hand side of the y axis shows a scale for the O2 concentration in volume %. An expiration process of a breath takes place in the time range of 0 sec up to about 1.3 sec, and an inhalation process of the next breath takes place in the range of 1.3 sec to 2.5 sec.

[0094] FIG. 3 shows the two time curves in the situation of FIG. 2, wherein a leak has occurred in the overall time period from the 1.sup.st measuring point up to the 250.sup.th measuring point. It can be seen that the two time curves of CO2 and O2 are no longer opposite, but rather a large overlap occurs in the overlapping area Ü.

[0095] FIG. 4 shows: the progress over time of the CO2 concentration, the progress over time of the O2 concentration, the progress over time of the concentration of an anesthetic (designated by Nm), and the progress over time of the pressure P.sub.cell in a measuring point of the gas sensor array 50.

[0096] In the time period of 0 to 120, which is shown in FIG. 4, the pump 55 is switched on continuously and suctions gas. The four time curves CO2, O2, Nm and P.sub.cell were scaled such that they can be shown on the same scale. The time in sec is plotted on the x axis.

[0097] It can be seen, on the one hand, that the fluctuations in the concentration of CO2, O2 and Nm follow after the fluctuations in the pressure P.sub.cell, because the pressure P.sub.cell travels approximately at the speed of sound and requires a travel of the variable gas concentrations in the removal hose 52 that is markedly longer than the pressure in order to reach the gas sensor array 50, for example, about 2 sec in case of a 3-m-long removal hose 52.

[0098] A leak L has occurred in time period T_L. This leak L leads to a markedly lower O2 concentration and to a somewhat lower CO2 concentration in the time period T_L. In addition, the peaks of the CO2 curve and of the O2 curve change their shapes. The CO2 curve shows in the time period T_L a “peak” per each breath, which occurs in terms of time close to the end of the phase of exhalation. The O2 curve has a rather trapezoidal or rectangular shape.

[0099] The signal processing unit 30 determines the respective time curve of the O2 concentration, of the CO2 concentration and optionally also the time curve of the N2O concentration and the time curve of the anesthetic concentration.

[0100] The signal processing unit 30 determines each breathing process and the phase of exhalation of this breathing process during the mechanical ventilation of the patient 20 based on the CO2 concentration with respect to time curve and/or on the O2 concentration with respect to time curve. In one embodiment, each phase of exhalation is such a time period between two zero crossings of the standardized CO2 concentration, in which the standardized CO2 concentration is greater than zero, cf. FIGS. 5a and 5b. A measured value CO2(i) and O2(i) for the CO2 concentration and for the O2 concentration at the time t(i) each is present at each sample time t(i) during an expiration process. The respective number of the measuring point is, in turn, plotted on the x axis. The sample frequency is 50 Hz in the example shown.

[0101] The signal processing unit 30 standardizes the measured values, which have been measured during an expiration process, to a range between −A and +A, wherein A is a predefined value. For the measured values of the O2 concentration, this standardization is preferably carried out according to the calculation rule

[00001]${O2}_{sk}\left(i\right)=A*\frac{2*O2\left(i\right)-\left[O{2}_{\max }+O{2}_{\min }\right]}{{O2}_{\max }-{O2}_{\min }}$

and by means of a corresponding calculation rule for the measured values of the CO2 concentration. Due to this standardization, a constant offset is also eliminated by calculation. In this calculation rule, O2.sub.max and O2.sub.min designate the largest value and the smallest value, respectively, for the O2 concentration during an expiration process. FIG. 5a shows the standardized curve of the example of FIG. 2. FIG. 5b shows the standardized curve of the example of FIG. 3. A=1000 in this case. Of course, a different value for A and a different calculation rule for the standardization are also possible.

[0102] The signal processing unit 30 calculates changes over time in the O2 curve and in the CO2 curve, for example, according to the calculation rule

ΔO2.sub.sk(i)=O2.sub.sk(i)−O2.sub.sk(i−s.sub.O2) as well as

ΔCO2.sub.sk(i)=CO2.sub.sk(i)−CO2.sub.sk(i−s.sub.CO2),

wherein s.sub.O2 and s.sub.CO2>=1 are two predefined or even calculated numbers (increments). As a result, two difference curves ΔO2.sub.sk and ΔCO2.sub.sk are calculated. The increments (sample size) s.sub.O2 and scot are preferably between 5 and 50. The sample frequency is, for example, 50 Hz. There is preferably a time period between 5*20 msec=100 msec and 50*20 msec=1 sec between the two sample times i and i-s.sub.CO2. The changes over time ΔO2.sub.sk and ΔCO2.sub.sk correlate with the derivatives of the concentration curves with respect to time.

[0103] The synchronization of the two time curves described below is preferably carried out. It is possible to use different increments s.sub.O2 and s.sub.CO2 for O2 and for CO2.

[0104] The sample increments s.sub.O2 and s.sub.CO2 have an effect on how reliably a leak L is detected and with sufficient certainty can be distinguished from a leak-free state. In one embodiment, experimentally different possible increments s.sub.O2 and s.sub.CO2 are tested for the sampled curve of the O2 concentration and for the sampled curve of the CO2 concentration. Which increments s.sub.O2 and s.sub.CO2 lead to good detection results may depend on the ventilation rate. It is possible to determine and store in advance one set each of readily suitable increments s.sub.O2 and s.sub.CO2 for different values of parameters of the mechanical ventilation. The parameters include especially the rate and the amplitudes of the ventilation strokes as well as ratio of inspiration to expiration over time. When the process shall be carried out, the values of the parameters currently used during the mechanical ventilation are determined, and the associated, stored set of increments s.sub.O2 and s.sub.CO2 is used.

[0105] In case the two determined and actually used increments are different from one another, a phase shift is brought about, which is preferably offset by calculation. For the offset by calculation, for example, the two difference curves ΔO2.sub.sk and ΔCO2.sub.sk are shifted over time in relation to each other until the minimum of the curve ΔCO2.sub.sk and the maximum of the curve ΔO2.sub.sk are at the same time after the shift.

[0106] Such an increment s.sub.O2 for O2 and such an increment s.sub.CO2 for O2 are determined and used for the following process, in which the maximum of ΔO2.sub.sk, i.e., the maximum of the changes of the standardized O2 values, and the minimum of ΔCO2.sub.sk, i.e., the minimum of the changes in the standardized CO2 values, are at the same time, optionally after the just described time shift. The maximum is designated by ΔO2.sub.sk,max and the minimum by ΔCO2.sub.sk,min in FIG. 6.

[0107] Subsequently, the signal processing unit 30 calculates for a sequence of sample times during an expiration process a sequence of arithmetic product values according to the calculation rule

Prod(i)=ΔO2.sub.sk(i)*ΔCO2.sub.sk(i).

[0108] If no leak L occurs, then, as a result, ΔCO2.sub.sk(i)>0 (CO2 concentration increases) and ΔO2.sub.sk(i)<0 (O2 concentration decreases) apply to each sample time t(i) during an expiration process. As a rule, conversely, ΔCO2.sub.sk(i)<0 and ΔO2.sub.sk(i) >0 apply during an inspiration process. Therefore, Prod(i)<0, as a result, during a full breath, because ΔCO2.sub.sk(i) and ΔO2.sub.sk(i) have different signs, provided no leak L has occurred. By contrast, in case a leak L has occurred, Prod(i) >0, i.e., with the same sign, applies to individual sample times t(i).

[0109] FIG. 6a shows the temporal change of ΔCO2.sub.sk, ΔO2.sub.sk and Prod (product value) resulting after the just described synchronization, which result from the example of FIG. 2 (no leak L has occurred). FIG. 6b shows the temporal change of ΔCO2.sub.sk, ΔO2.sub.sk and Prod, which result from the example of FIG. 3 (leak L occurred). Furthermore, an area identified by >0, in which Prod(i) >0, is shown in FIG. 6b.

[0110] The signal processing unit 30 preferably calculates the product values Prod(i) for each expiration process only, but not for an inspiration process. A leak L has a markedly stronger effect during an expiration process than during an inspiration process, which can be readily seen in FIG. 3. A leak L is also detected rapidly enough in this embodiment, and calculation time is saved. In the example of FIG. 6 an expiration process takes place in the time period between the 1.sup.st measuring point and the 120.sup.th measuring point.

[0111] A leak L shall be able to be distinguished from other disturbing effects. Such a disturbing effect may result, for example, from the fact that drops of liquid or condensate clog the diaphragm of the water trap 51 until condensed liquid drips into a tank of the water trap 51 or is transported into same and then the diaphragm abruptly has a higher permeability. This abrupt higher permeability could simulate a leak, which is not, in fact, present.

[0112] In one embodiment, the signal processing unit 30 calculates the sum DiPhaC of all product values Prod(i) during an expiration process that are greater than 0. DiPhaC means “Differential in Phase Covariance.” Except for numerical deviations, this sum DiPhaC is proportional to the surface of the area identified by >0 in FIG. 6b. In case this sum DiPhaC is above a predefined threshold, then the signal processing unit 30 has detected a leak L or at least an indication that a leak L has occurred. In one embodiment, the signal processing unit 30 then generates a message that a leak L has been detected.

[0113] The just described process with the sum DiPhaC has a plurality of advantages compared with other processes in order to detect a leak L. As long as a leak L occurs, Prod(i) is >0. As soon as the leak L is plugged or is otherwise eliminated, Prod(i) is again <=0. The process with DiPhaC is therefore capable not only of detecting an abruptly occurring leak L, but also a gradually increasing leak L, which may result, for example, from material fatigue. The advantageous effect that different types of leaks can be detected results especially from the fact that the process with DiPhaC does not require comparing a current measured value or a derived value with a reference value, which refers to an earlier sample time.

[0114] The process with DiPhaC has, in addition, the following advantage in comparison to the possible procedure of calculating a statistical indicator of the phase shift between the CO2 concentration and the O2 concentration and of comparing this statistical indicator with a limit: The limit, with which the statistical indicator is compared, must be adapted to at least one parameter of the ventilation, for example, to the pressure or to the rate of the mechanical ventilation or to a physiological state of the patient 20. This limit is frequently automatically set as a function of measured values, and these measured values are measured during a leak-free state. The process with DiPhaC does not require such prior knowledge or background knowledge to set a limit and also does not require a leak-free state. Therefore, no initialization phase is needed.

[0115] FIG. 7 shows the result of a test, in which a leak was generated in a targeted manner. In order to generate a leak L in a targeted manner, an actuatable solenoid valve with a ruby perforated stone was installed in an area at the or close to the inlet of the gas sensor array 50, namely at the point L of FIG. 1. In the fully open position of the solenoid valve, a leak L is created that is so large that the volume flow of the ambient air suctioned through the leak L is about 20% of the entire volume flow of the gas mixture (breathing gas sample and ambient air), which gas mixture flows through the gas sensor array 50. In case such a leak L is not eliminated, the measurement results of the gas sensor array 50 will be considerably distorted.

[0116] A leak L was generated in each of the time periods T_Ll, . . . , T_L4. A scale for the position of the valve from 0 (fully closed) to 1 (fully open) is shown on the right-hand side of the y axis. A scale for DiPhaC is shown on the left-hand side of the y axis. The diagram of FIG. 7 shows the time curve (time profile) of the pressure P.sub.cell at the gas sensor array 50 and the time curve of DiPhaC. The pressure P.sub.cell was averaged over a respective breathing phase of the patient 20, so that each measured value refers to precisely one breathing phase. The consecutive numbers of breathing phases are plotted on the x axis. The duration of a breathing phase may vary over time. s.sub.CO2=26 and s.sub.O2=25 were used as exemplary increments for CO2 and O2. It can be seen that a leak L always leads to a value greater than 1000 for DiPhaC, while other effects always lead to a smaller value, namely less than half. Hence, in this case any occurrence of a leak L is detected, and a nuisance alarm is avoided.

[0117] The process, which is based on the signal DiPhaC, is preferably complemented by an additional process. Thus, two leak criteria are used, namely DiPhaC as the first leak criterion and a second leak criterion with the designation DPC (“Delta Pressure Covariance”). This additional process is capable with greater certainty of reliably detecting an abruptly occurring leak, especially even with a low or only relatively slightly varying ventilation pressure and/or with a high ventilation rate. A low ventilation pressure or a low amplitude of the ventilation pressure in conjunction with a high ventilation rate are especially used when a child is mechanically ventilated.

[0118] The signal processing unit 30 calculates values for the covariance Cov[CO2,O2] between the time curve of the CO2 concentration and the time curve of the O2 concentration multiple times in each case during each phase of exhalation. This covariance Cov[CO2,O2] varies over time. For a plurality of consecutive sample times, the signal processing unit 30 calculates a value for the covariance Cov[CO2,O2] using n respective values for the CO2 concentration and the O2 concentration.

[0119] The signal processing unit 30 applies, for example, the following calculation rule:

[00002]$\mathrm{Cov}\left[\mathrm{CO}2,O2\right]\left(m\right)=\frac{2}{n}\underset{i=1}{\stackrel{n}{.Math.}}\frac{\begin{array}{c}\mathrm{CO}2\left(m+i\right)-\\ \mathrm{CO}{2}_{avg}\end{array}}{\begin{array}{c}{\mathrm{CO}2}_{\max }-\\ \mathrm{CO}{2}_{\min }\end{array}}\star \frac{O2\left(m+i\right)-O{2}_{avg}}{{O2}_{\max }-{O2}_{\min }}$

In this calculation rule, O2.sub.max and O2.sub.min designate the largest and the smallest value, . . . , respectively, for the O2 concentration under the n values for the n sample times t(m+1), t(m+n). O2.sub.avg designates the arithmetic mean value of these n values. This covariance Cov[CO2,O2] is an indicator of the phase shift between the CO2 concentration, which is variable over time, and the O2 concentration, which is variable over time, in this measuring time period. If no leak has occurred, then the covariance is ideally −1; it is between −0.6 and −0.8 for all practical purposes.

[0120] FIG. 8 shows, as an example, the time curve of the CO2 concentration and the time curve of the covariance Cov[CO2,O2] between CO2 and O2. A scale for the CO2 concentration is plotted on the left-hand side of the y axis, and a scale for the covariance is plotted on the right-hand side of the y axis. The consecutive number of breathing phases is, in turn, plotted on the x axis.

[0121] The covariance Cov[CO2,O2]—or another indicator of the phase shift between the two time curves CO2 and O2—is greater in the time period, in which a leak occurs, than in a leak-free time period. However, the value of the covariance Cov[CO2,O2] is not only influenced by the occurrence and the size of the leak L, but also by a variety of other factors, especially by the ventilation pressure, by the ventilation rate and whether the ventilation is carried in a volume-controlled manner or in a pressure-controlled manner.

[0122] The procedure described below is in many cases capable of eliminating this drawback, without the consequences of the other factors on the covariance Cov[CO2,O2] having to be known. A basic concept is the procedure of calculating and analyzing the change over time of the covariance. This change in the covariance Cov[CO2,O2] indicates a suddenly occurring leak L.

[0123] Furthermore, the signal processing unit 30 calculates a change

ΔCov[CO2,O2](m)=Cov[CO2,O2](m)−Cov[CO2,O2](m−s.sub.Cov)

of the covariance Cov[CO2,O2] with a predefined increment s.sub.Cov, for example, s.sub.Cov=1. Moreover, the signal processing unit 30 calculates a change

ΔP.sub.Cell(j)=P.sub.Cell(j)—P.sub.cell(j−s.sub.Cell)

of the pressure P.sub.Cell. In the example shown, each used value for this pressure Pull is averaged over a respective breathing phase. The sample time t(j) for the pressure P.sub.Cell is positioned in respect to time in a suitable manner in relation to the covariance Cov[CO2,O2], for example, j=m+n. This positioning in respect to time may depend on the interval between the gas sensor array 50, which measures the concentrations, and a measuring point, at which the pressure sensor 57 measures the pressure, as well as on the flow rate of the suctioned breathing gas sample through the removal hose 52.

[0124] The pressure P.sub.Cell may, for example, change rapidly when a larger quantity of fluid, and especially of condensed water, with the stream of the suctioned breathing gas sample reaches the measuring system 110 and is collected in front of the diaphragm of the water trap 51. When this quantity of fluid flows or is fed abruptly into the tank of the water trap 51, then the diaphragm is released abruptly.

[0125] FIG. 10 shows, as an example, the time curves of ΔCov[CO2,O2] and ΔP.sub.Cell. The consecutive numbers of the breathing phases of the patient 20 are, in turn, plotted on the x axis. The scale for the dimensionless variable ΔCov[CO2,O2] is plotted on the left-hand side of the y axis, and the scale for the variable ΔP.sub.Cell in hPa is plotted on the right-hand side of the y axis. A leak L has occurred in the two time periods T_L.1 and T_L.2. The first occurrence of the leak L leads to the peak Sp_P.1 of the curve of ΔP.sub.Cell and the peak Sp_Cov.1 of the curve of ΔCov, and the second occurrence leads to the peaks Sp_P.1 and Sp_Cov.1, i.e., to abruptly increasing values. The closing of the leaks L leads to two respective peaks in the opposite direction, i.e., to abruptly decreasing values.

[0126] The signal processing unit detects a leak L as a function of the values for ΔCov[CO2,O2] and ΔP.sub.Cell. In case, for example, both ΔCov[CO2,O2](j) and ΔP.sub.Cell(j) are each above a predefined threshold at a sample time t(j), then a leak L has occurred at this sample time t(j). This process yields a signal, which is designated below as “Delta Pressure Covariance” (DPC). It is also possible to calculate the covariance between ΔCov[CO2,O2] and ΔP.sub.Cell. In case this covariance is above a predefined threshold, for example, is greater than 0, then a leak L is detected.

[0127] The process with the signal DPC frequently also detects, even in case of low ventilation pressures, i.e., low amplitudes of the CO2 curve and of the O2 curve, as well as at high respiration rates a suddenly occurring leak L in a reliable manner. Only relatively few nuisance alarms are generated, often no nuisance alarms at all.

[0128] Both processes DiPhaC and DPC are preferably used in order to detect a leak. A leak L is detected when either DiPhaC or DPC or both criteria generate a signal for the occurrence of a leak L. It is, however, also possible to apply only one of the two criteria.

[0129] FIG. 9 and FIG. 11 show the two processes DiPhaC and DPC for detecting a leak L, wherein a patient 20 is mechanically ventilated with a ventilation pressure having a relative high rate and a relatively low amplitude and wherein a suddenly occurring leak L was generated by tests by means of the above-descried solenoid valve 15 times one after the other. FIG. 9 and FIG. 11 show each the curve of the pressure P.sub.cell at the inlet of the gas sensor array 50, wherein, in turn, each measured value shown indicates the pressure P.sub.Cell averaged over a breathing phase of the patient and the consecutive numbers of the breathing phases of the patient 20 are plotted on the x axis. A respective value of the pressure P.sub.Cell is shown per breathing phase. This shown value is generated, for example, by averaging over a plurality of measured values. The right-hand side of the y axis in both figures indicates the values from −68 to −52 of the pressure P.sub.cell hPa. FIG. 9 shows, furthermore, the time curve of the signal DiPhaC, FIG. 11 shows the signal DPC. The left-hand side of the y axis in both figures shows a scale for this signal. The signal DPC has only the values 0 and 1. In this situation, the process DiPhaC is not capable of detecting the first and the second suddenly occurring leak L, while the process DPC automatically detects all 15 occurring leaks L.

[0130] When a leak L has been detected by means of at least one of the processes DiPhaC or DPC, then the gas sensor array 50 transmits a corresponding message to the control device 35. After reception of such a message, the control device 35, in one embodiment, immediately triggers an alarm in a manner perceptible by a person.

[0131] In another embodiment, the control device 35, after reception of such a message, first triggers a check whether a leak L has actually occurred that must be eliminated immediately, or else another event that simulates a leak L but does not make any intervention necessary. This check reduces the number of nuisance alarms, without an actually occurring leak L being overlooked. The mechanical ventilation of the patient 20 is continued during this check and is not impaired by the check. In the exemplary embodiment, this check is carried out when the ventilator 100 reaches a positive ventilation pressure above a predefined threshold, i.e., emits breathing gas.

[0132] The check whether a leak L has actually occurred comprises in one embodiment the following steps: The pump 55 of the gas sensor array 50 is switched off for the duration of the check. The pressure sensor 58 continues to measure the ambient pressure P.sub.amb. The pressure sensor 57 of the gas sensor array 50 continues to measure the pressure P.sub.cell,abs, which is present at the end of the removal hose 52. The pressure sensor 36 in the ventilation circuit 40 continues to measure the pressure in the ventilation circuit 40, for example, the pressure P.sub.aw.

[0133] As is known, the pressure travels at the speed of sound. Except for unavoidable measurement errors and the process noises, the time curve of the pressure P.sub.cell in the removal hose 52 coincides with the time curve of the pressure P.sub.aw in the ventilation circuit 40, provided no leak has occurred. Because the pump 55 is switched off, a possible clog or other impairment of the diaphragm at the water trap 51 has no effect on the measurement. A reference value, which has been measured before checking for the leak, is not needed

[0134] In one embodiment, the decision whether or not a leak L has actually occurred is made as follows: The pump 55 is switched off. The pressures P.sub.Cell in the removal hose 52 and P.sub.aw in the ventilation circuit 40 are subsequently compared with one another. For this comparison, the pressure in the ventilation circuit 40, for example, the ventilation pressure P.sub.aw present at the patient 20, the pressure P.sub.cell,abs, which is present at the gas sensor array 50, as well as the ambient pressure P.sub.amb are measured at n consecutive sample times t(1), t(n). The ambient pressure P.sub.amb is measured by the pressure sensor 58 and is especially therefore measured and used, because it may vary over time and this variation over time shall not distort the comparison of relative pressures.

[0135] The variable

ΔP.sub.max=Max{P.sub.aw[t(1)], . . . , P.sub.aw[t(n)]}−Max{P.sub.cel,absl[t(1)]−P.sub.amb[t(1)], . . . , P.sub.cell,abs[t(n)]−P.sub.amb[t(n)]}

is calculated. This variable ΔP.sub.max is ideally equal to the maximum loss of pressure which occurs between the ventilation circuit 40 and the gas sensor array 50 and changes in case of the occurrence of a leak L. A pressure limit P.sub.limit is calculated as a function of the ventilation pressure P.sub.Insp, which the delivery unit 24a generates in the ventilation circuit 40 during the inspiration process, as well as a function of the ventilation rate RR. A leak L is detected when

ΔP.sub.max>P.sub.limit.

[0136] In case no leak has occurred, then the ambient pressure P.sub.amb ideally has no effect on the calculated variable, and

ΔP.sub.max=0.

[0137] The just described procedure takes into account the ambient pressure P.sub.amb, which has a significant effect on the calculated variable ΔP.sub.max only in case of a leak L, and hence is able to distinguish a leak L from a disturbance variable better than other processes.

[0138] 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 CHARACTERS

[0139]

TABLE-US-00001 20 Patient, who is mechanically ventilated, connected to the coupling unit 21 on the patient side 21 Patient-side coupling unit in the form of a mouthpiece or a breathing mask, connected to the Y-piece 22 22 Y-piece, which connects the patient-side coupling unit 21 to a feed line for the feed of gas (inhalation, inspiration) and a discharge line for the discharge of gas (exhalation, expiration)  23a Nonreturn valve, which lets through a gas flow in the direction of the patient 20 in the inhalation line 32 and blocks same in the opposite direction  23b Nonreturn valve, which lets through a gas flow away from the patient 20 in the exhalation line 33 and blocks same in the direction toward the patient 20  24a Delivery unit, which generates a volume flow in the direction of the patient 20  24b PEEP valve, which maintains a pressure in the lungs of the patient 20  25a Carbon dioxide absorber, absorbs carbon dioxide from the ventilation circuit 40 26 Manual ventilation bag, via which the ventilation circuit 40 can be driven 27 Fluid stream of fresh air or other fresh gas to the ventilation circuit 40 28 Fluid stream of anesthetic in vapor form to the ventilation circuit 40 29 Adjustable overpressure valve, which is capable of releasing gas from the ventilation circuit 40 30 Data-processing signal processing unit for the gas sensor array 50, analyzes signals from the sensors 53, 54, 57 and 58, is capable of detecting a leak L and of transmitting a message to the control device 35 31 Anesthetic vaporizer, generates the anesthesia stream 28 32 Breathing gas line for inhalation, connected to the Y-piece 22, has the nonreturn valve 23a 33 Breathing gas line for exhalation, connected to the Y-piece 22, has the nonreturn valve 23b 34 Branching-off point of the removal hose 52 35 Control device, actuates the delivery unit 24a and the anesthetic vaporizer 31, receives signals about the respective gas concentration and messages from the signal processing unit 30, generates an alarm about a leak L that has occurred, as needed 36 Pressure sensor in the ventilation circuit 40, preferably measures the pressure P.sub.aw present at the patient 20 40 Ventilation circuit, through which the patient 20 is mechanically ventilated and sedated, connects the patient 20 to the ventilator 100, comprises the patient-side coupling unit 21, the Y-piece 22, the inhalation line 32 and the exhalation line 33 50 Gas sensor array, which measures the concentration of O2, CO2, N2O and anesthetic, comprises the gas sensors 53 and 54, the pump 55 as well as the pressure sensor 57 51 Water trap upstream of the gas sensor array 50, comprises at least one diaphragm, which is preferably made of PTFE, and a tank 52 Removal hose, through which a breathing gas sample is taken from the ventilation circuit 40, begins in a branching-off point 34 between the patient-side coupling unit 21 and the Y-piece 22 and leads to the water trap 51 53 Sensor for the O2 concentration in the breathing gas sample 54 Sensor for the concentration of CO2, H2O and anesthetic in the breathing gas sample 55 Pump, which suctions a breathing gas sample into the removal hose 52 56 Discharge hose, through which a breathing gas sample is fed again into the ventilation circuit 40, leads to a feed point upstream of the carbon dioxide absorber 25a 57 Pressure sensor of the gas sensor array 50, measures the pressure P.sub.Cell 58 Sensor for the ambient pressure P.sub.amb 100  Ventilator, configured as an anesthesia apparatus, comprises the optional anesthetic vaporizer 31, the delivery unit 24a, the carbon dioxide absorber 25a, the pressure sensor 36, the nonreturn valves 23a and 23b, the PEEP valve 24b and the manual ventilation bag 26 110  Measuring system, comprises the gas sensor array 50, the water trap 51 and the signal processing unit 30 Cov[CO2, O2] Covariance between the time curves of the CO2 concentration and of the O2 concentration DiPhaC “Differential in Phase Covariance,” first leak criterion based on time periods with the same sign DPC “Delta Pressure Covariance,” second leak criterion based on the changes in covariance and pressure L Exemplary leak in the transition between the removal hose 52 and the water trap 51 P.sub.aw Breathing and ventilation pressure present at the patient 20, measured by the sensor 36 P.sub.amb Ambient pressure, measured by the sensor 58 P.sub.Cell Pressure at the inlet of the gas sensor array 50, preferably the pressure in relation to the ambient pressure P.sub.amb P.sub.cell, abs Absolute pressure at the inlet of the gas sensor array 50, measured by the sensor 57 P.sub.limit Lower limit for the check whether a leak has actually occurred T_L, T_L.1, Time period, in which a leak L has occurred between the branching-off T_L.2 point 34 and the gas sensor array 50