Abstract:
A method for controlling the end-expiratory pressure at a patient ( 30 ) in a respiratory system ( 50 ) of an anesthesia apparatus or respirator ( 30 ) includes regulating a pressure curve ( 401   a,    401   b,    501   a,    501   b ) during the expiration phase ( 650 ) of the patient such that the pressure curve is described by an at least partially dropping curve ( 105   a,    105   b,    106   a,    106   b,    601, 602, 603, 604 ) from a first upper pressure value ( 613   a,    613   b,    613   c,    613   d ) to a first lower pressure value ( 614   a,    614   b,    614   c,    614   d ) from the end of the inspiration phase ( 660 ) until the beginning of the next, following inspiration phase ( 670 ). An anesthesia apparatus or respirator is provided that includes an operating and actuating unit that regulates a controllable expiratory valve and a respiration drive such that the pressure curve is described by an at least partially dropping curve.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase Application of International Application PCT/EP2012/000495 filed Feb. 3, 2012 and claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2011 106 406.4 filed Jul. 2, 2011, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a method for controlling an end-expiratory pressure at the end of the expiration phase, the so-called expiration phase of a patient in a respiratory system of an anesthesia apparatus or of a respirator. 
       BACKGROUND OF THE INVENTION 
       [0003]    During the mechanical respiration of a patient by means of an anesthesia apparatus or a respirator, the pressure is reduced at the end of expiration to the extent that the patient can breathe out. The pressure level is not lowered now completely to the prevailing ambient pressure, but there remains a residual pressure, the so-called positive end-expiratory pressure (PEEP), in the lung. This pressure is maintained at a constant level by means of the anesthesia apparatus or respirator during expiration until the next inspiration. Any possible leaks in the connection from the anesthesia apparatus or respirator to the patient are compensated by a pressure regulator by the pressure regulator adjusting a volume by means of supplying a rate of flow to the extent that the positive end-expiratory pressure can be maintained in the patient&#39;s lungs. Due to this slight overpressure in the lungs against the ambient pressure, it is ensured by a distension of the lungs that the opened areas in the lungs will not collapse again during expiration during the time until the next inspiration and the exchange area of the lungs will not be reduced hereby. 
         [0004]    A suctioning measuring system is connected in many cases by means of a flexible tube in anesthesia systems directly at the connection piece to the patient, in which the expiratory and inspiratory breathing tubes are brought together, the so-called Y-piece, and gas is sent with a suction volume flow directly from the patient into the measuring system, and the physiological respiration parameters of the patient are analyzed in the measuring system. For example, the oxygen concentration and the carbon dioxide concentration (C CO     2   ) are recorded over time. Especially the carbon dioxide concentration (C CO     2   ) at the end of expiration by the patient, the so-called end-tidal concentration (etCO 2 ), is of diagnostic and therapeutic significance here. This makes it possible to infer how sufficient the patient&#39;s respiration, i.e., the supply with oxygen, is. The physician makes decisions about adjusting the respiration, for example, the respiration rate, the minute volume, the pressure settings, as well as the selected, administered oxygen concentration. 
         [0005]    The adjustment of the positive end-expiratory pressure by a pressure regulator in the respiratory system causes fresh gas to be delivered directly to the patient to the so-called Y-piece. This fresh gas mixes there with the air expired by the patient. This mixed air is suctioned off from the patient, from the Y-piece, to the measuring arrangement. The suctioning takes place typically with a suction line, typically by means of a very thin suction tube with an internal diameter in the range of 0.5 mm to 1.5 mm over a length of 1.5-3.0 m. A suction volume flow of typically about 0.2 L/minute delivers the air through the suction tube from the patient into the measuring arrangement. The gas thus reaches the measuring arrangement with a delay in the range of about 0.8 sec to 3.5 sec due to its path and the type of suctioning. If additional components with an additional volume, for example, a water trap, are arranged in the suction line on the path to the measuring arrangement, and if the volume in the measuring arrangement itself, as well as the necessary measuring time for determining the carbon dioxide concentration in the measuring arrangement are taken into account, the delay between the location of the test sample at the patient and a value of a carbon dioxide concentration, which value is determined by measurement and displayed, increases, on the whole, to a value in the range of about 3 sec to 10 sec. 
         [0006]    Such a delay corresponds approximately to a number ranging from less than one breathing cycle to two breathing cycles for an adult, to 1 to 6 breathing cycles for an infant as well as to 3 to 10 breathing cycles for a newborn. 
         [0007]    Depending on the type of pressure regulation and the situation prevailing at the patient, at the respiratory system, the respiration parameters selected and the leaks present in the system, the regulated adjustment of the positive end-expiratory pressure causes the carbon dioxide concentration (C CO     2   ) at the measuring arrangement not to correspond to the concentration that is present in the pharyngeal space and the bronchial space of the patient during expiration. A respiratory system with a regulator for setting a positive end-expiratory pressure is known from the document U.S. Pat. No. 4,082,093. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to provide a method that makes it possible to set the positive end-expiratory pressure in a respiratory system of a respirator or anesthesia apparatus such that the measured values of the carbon dioxide concentration (C CO     2   ) in the CO 2  measuring arrangement are not affected by the pressure regulation. 
         [0009]    According to the invention, a method is provided for controlling the end-expiratory pressure at a patient in a respiratory system of an anesthesia apparatus or respirator. A pressure curve is regulated during the expiration phase of the patient such that the pressure curve is described by an at least partially dropping curve from a first upper pressure value to a first lower pressure value from the end of the inspiration phase until the beginning of the next, following inspiration phase. 
         [0010]    According to another aspect of the invention, an anesthesia apparatus or respirator is provided comprising a patient connection, a gas pressure regulating arrangement for regulating gas pressure at the patient connection and an operating and actuating unit. The operating and actuating unit is connected to the gas pressure regulating arrangement for regulating pressure to the patient during an inspiration phase and during an expiration phase such. The expiration phase, from the end of the inspiration phase to the beginning of the following inspiration phase, is described by an at least partially dropping curve from an upper pressure value to a lower pressure value. 
         [0011]    Provisions are made in the manner according to the present invention for the control circuit for the positive end-expiratory pressure in the respiratory system of an anesthesia apparatus or respiratory system to be controlled in such a manner that the mixing at the Y-piece does not affect the measured values of the suctioning gas concentration measurement, especially of the CO 2  measurement. The pressure regulator is controlled such that the positive end-expiratory pressure for the breathing-out phase—the so-called expiration phase—of the patient is not maintained at an absolutely constant pressure level, but the pressure level of the positive end-expiratory pressure (PEEP) at the end of the expiration phase is selected to be lower than the pressure level of the positive end-expiratory pressure (PEEP) at the beginning of the expiration phase and is stabilized. Instead of a constant pressure level, a dropping pressure ramp is used to this end according to the present invention for the regulation as a set value for the pressure regulator of the positive end-expiratory pressure (PEEP) in the course of the expiration phase. The pressure levels at the end and at the beginning of the expiration phase are preferably determined in this case from a predetermined mean value of the positive end-expiratory pressure (PEEP). The pressure regulation is not affected according to the present invention during the breathing-in phase, the so-called inspiration phase. 
         [0012]    In a first embodiment of the present invention, the dropping pressure ramp is described by a first upper pressure value and a first lower pressure value. The mean value between the first upper pressure value and the first lower pressure value represents the desired positive end-expiratory pressure, so that there is no change for the patient in the pressure ratio present relative to the ambient pressure as an average compared to a constant positive end-expiratory pressure stabilized at a constant pressure level over the duration of the expiration phase. 
         [0013]    The duration of the expiration phase and of the inspiration phase is defined by the respiration parameters selected, such as the respiration rate combined with the so-called I/E ratio, i.e., the ratio of the inspiration phase to the expiration phase. The first upper pressure value and the first lower pressure value are determined from this duration of the expiration phase and the desired positive end-expiratory pressure value set by the user. In a preferred embodiment, the determination of the first upper pressure value and of the first lower pressure value is described by a linearly dropping pressure curve or by a nonlinearly dropping pressure curve during the expiration phase. 
         [0014]    A linear curve also includes, in the sense of the present invention, any curve that obeys a linear equation of a straight line. A nonlinear curve also includes, in the sense of the present invention, any curve that obeys a square or cubic function or a higher-order polynomial. Also included are, furthermore, logarithmic or exponential curves as well as generally progressively or degressively dropping functions, which are suitable for determining a first upper pressure value and a first lower pressure value from the duration of the expiration phase and the mean, desired value for the positive end-expiratory pressure. 
         [0015]    The function is discontinuous in another preferred embodiment. This means that a linearly dropping function or a nonlinearly dropping function does not have a continuous curve with dropping slope, but the curve is stepped. The positive end-expiratory pressure is lowered in this variant from a first upper pressure level in steps to a first lower pressure level, and the mean level of the positive end-expiratory pressure, which was selected by the user for the patient in question, will again become established as the mean value between the first upper pressure level and the first lower pressure level. 
         [0016]    In another preferred embodiment of the present invention, the dropping curve from a first upper pressure level to a first lower pressure level does not take place over the entire duration of the expiration phase. The curve of the positive end-expiratory pressure is partially constant and partially dropping in this further preferred embodiment. The positive end-expiratory pressure is maintained at an upper pressure level at the beginning of the expiration phase for a certain duration at the end of the inspiration phase in this further preferred embodiment. Beginning from a certain time during the expiration phase, the pressure is lowered from the upper pressure level to a lower pressure level according to a dropping curve. This leads to a combination of an upper, constant pressure level for a time delay of a predetermined duration at the beginning of the expiration phase with a subsequent drop in pressure, so that a stronger gradient is obtained from the upper pressure level to the lower pressure level for the remaining duration of the expiration phase. In this further preferred embodiment according to the present invention, this increased pressure gradient causes the phase during which the CO 2 -containing air is delivered from the patient&#39;s lungs into his oral cavity to the Y-piece to be prolonged for the patient. This variant is especially advantageous if the expiration times are comparatively long, i.e., such a control according to a dropping pressure curve with a constant component preceding the time delay is especially advantageous in case of low respiration rates of 6-10 breaths per minute. 
         [0017]    The settings on the anesthesia apparatus and respirator, which the user has made for controlling the respiration of the patient, namely, the preset PEEP settings themselves, preferably in the form of a preset mean PEEP value (  PEEP ), as well as the ratio of the inspiration time to the expiration time, the so-called I/E ratio, and the respiration rate RR, are also taken into account for designing the pressure curve during the expiration phase in another preferred embodiment. 
         [0018]    In another preferred embodiment, the properties of the measuring device are taken into account as well. Both the length of the tube, the diameter of the tube and the suction volume flow are taken into account as well. The volume of gas that reaches the measuring means as a quantity of gas from the patient, namely, from the Y-piece, in the tube to the measuring device, is obtained from the length of the tube and the diameter of the tube. The time delay that occurs from the Y-piece and the pressure and concentration values present there until this quantity of air arrives at the measuring arrangement for the analysis is obtained from the suction volume flow and the volume. This suction time delay is taken into account in this preferred embodiment by coordinating the selection of the time delay at the beginning of the expiration time and also the selection of the upper pressure value and of the lower pressure value with the measuring time delay for the CO 2  measurement. 
         [0019]    The measuring time needed in the measuring arrangement for the determination and selection of the time delay at the beginning of the expiration time and of the upper as well as lower pressure values is also taken into account in another preferred embodiment. 
         [0020]    Typical values for an upper pressure value and a lower pressure value for a linearly dropping pressure curve during the expiration phase, which are typical parameter settings for the respiration rate, positive end-expiratory pressure and I/E ratio for three different types of patients, are shown below. A typical value for the three selected patient types is set as the mean positive end-expiratory pressure. The three patient types differ essentially in that the respiration must be performed according to different criteria and with different parameter settings, because the lungs of the patients are different in terms of their pneumatic properties. These include the volume, compliance and pneumatic resistance. The pneumatic properties of patients can be assigned to different patient types in a simplified manner based on the body weight. 
         [0021]    These three patient types include as a first example an adult with a typical body weight of about 70 kg, and a child with a typical body weight of about 10 kg is selected as a second example, and a newborn baby with a typical body weight about 2 kg is selected as a third example. 
         [0022]    Different values are obtained for the lung volume and different respiration rates are obtained for these three patient types, and they result in different conditions for the respiration. 
         [0023]    Table 1 below shows typical mean values for body weight, lung volume V, minute volume MV, respiration rate RR, I/E ratio, inspiration time T i , expiration time T e  and inspiration pressure P insp  as well as expiration pressure (PEEP). 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Body 
                 V 
                 MV 
                 RR 
                 I/E 
                 P insp   
                 PEEP 
                 T i   
                 T e   
               
               
                 weight 
                 [mL] 
                 [L] 
                 [1/minute] 
                 ratio 
                 [hPa] 
                 [hPa] 
                 [sec] 
                 [sec] 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 ~70 kg 
                 600 
                 4.8 
                 8 
                 1:2 
                 15 
                 5 
                 2.5 
                 5 
               
               
                 ~10 kg 
                 200 
                 3.0 
                 15 
                 1:2 
                 15 
                 5 
                 1.33 
                 2.66 
               
               
                  ~2 kg 
                 30 
                 1.5 
                 50 
                 1:1 
                 15 
                 5 
                 0.6 
                 0.6 
               
               
                   
               
             
          
         
       
     
         [0024]    Assuming a linear curve in this calculation example, a first upper pressure value and a first lower pressure value can then be determined from the values in this table. 
         [0025]    Table 2 below shows typical mean values for an upper pressure value (PEEP High ) and a lower pressure value (PEEP Low ) for the three patient types, namely, adult, child and newborn baby. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 PEEP 
                 PEEP High   
                 PEEP Low   
               
               
                   
                 Body weight 
                 [hPa] 
                 [hPa] 
                 [hPa] 
               
               
                   
                   
               
             
             
               
                   
                 ~70 kg 
                 5 
                 5.2 
                 4.8 
               
               
                   
                 ~10 kg 
                 5 
                 5.2 
                 4.8 
               
               
                   
                  ~2 kg 
                 5 
                 3.2 
                 2.8 
               
               
                   
                   
               
             
          
         
       
     
         [0026]    An exemplary calculation was performed here for the special embodiment with a time delay at the beginning of the expiration phase, before the dropping pressure ramp starts, for the first example with an adult of 70 kg according to Tables 1 and 2. 
         [0027]    With the data as boundary conditions according to Tables 1 and 2 and with the selected time delay corresponding to half the expiration time of 5 sec, i.e., a time delay of 2.5 sec, a first upper pressure value of 5.2 hPa and a first lower pressure value of 4.8 hPa are obtained for an adult with a body weight of 70 kg for the regulation of the positive end-expiratory pressure during the expiration phase of a patient. 
         [0028]    Due to the use of the time delay at the beginning of the expiration phase, the pressure gradient becomes steeper towards the end of the expiration phase compared to the embodiment with a pressure ramp that already drops at the beginning of the expiration phase. The steeper pressure gradient causes the patient to be able to expire nearly until the end of the expiration, so that the measurement of the carbon dioxide concentration can also take place towards the end of the expiration without mixing with the inspiration gas. 
         [0029]    The setting of the upper pressure value and of the lower pressure value can be performed for the special embodiment with a time delay at the beginning of the expiration phase before the start of the dropping pressure ramp in the same manner as in case of the use of the dropping pressure ramp without a time delay, so that the time delay leads, as was described above, merely to a steeper pressure gradient. 
         [0030]    However, it is also possible in one technical embodiment, and this possibility is also covered by the present invention, to lower the lower pressure value towards the end of the expiration phase, so that a greater pressure difference is additionally obtained besides the steeper pressure gradient. With a selected time delay corresponding to half of the expiration time of 5 sec, namely, a time delay of 2.5 sec, a first upper pressure value of 5.2 hPa to 5.3 hPa and a first lower pressure value of about 4.6 hPa to 4.7 hPa are obtained in such a variant, for example, according to the above example for a patient with a body weight of 70 kg. 
         [0031]    It can be postulated as a criterion for setting the upper pressure value and the lower pressure value that the positive end-expiratory pressure does not differ, on average, over the expiration phase for the patient from the positive end-expiratory pressure in case of constant stabilization. 
         [0032]    The present invention will be explained in more detail now on the basis of a number of figures and the corresponding description of the figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    In the drawings: 
           [0034]      FIG. 1  is a schematic view of a respiratory system according to the invention 
           [0035]      FIG. 2  is a first curve of the pressure, flow and carbon dioxide concentration (C CO     2   ) over two breathing cycles of a patient without adjustment of the positive end-expiratory pressure; 
           [0036]      FIG. 3  is a second curve of the pressure, flow and carbon dioxide concentration (C CO     2   ) over two breathing cycles of a patient with constant adjustment of the positive end-expiratory pressure; 
           [0037]      FIG. 4  is a third curve of the pressure, flow and carbon dioxide concentration (C CO     2   ) over two breathing cycles of a patient with adjustment of the positive end-expiratory pressure according to a dropping pressure curve; 
           [0038]      FIG. 5  is a variant of the curve according to  FIG. 4 ; 
           [0039]      FIG. 6   a  is a detail views according to  FIG. 5 ; 
           [0040]      FIG. 6   b  is a detail views according to  FIG. 4 ; 
           [0041]      FIG. 6   c  is a detail views according to a modification of  FIG. 5 ; and 
           [0042]      FIG. 6   d  is a detail views according to a modification of  FIG. 4 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0043]    Referring to the drawings in particular,  FIG. 1  schematically shows an arrangement  10  comprising a respiratory system  50  with a patient  30  and with an anesthesia apparatus  90  as well as with a measuring arrangement  70 . Measuring arrangement  70  comprises in its interior a measuring unit  75 , an analyzing and operating unit  71  as well as a corresponding display element  73 . Furthermore, a pump  77 , which suctions a quantity of air from the patient  30  via the Y-piece  51  and from the suction port  53  by means of a suction line  59  into the measuring arrangement  70  and passes same on to the ambient area  80  or into a discharge means provided for that purpose, is arranged in measuring arrangement  70 . The respiratory system  50  is connected to the patient  30  via port elements  56  and a flexible tube system. The flexible tube system comprises a Y-piece  51  with a suction port  53 , with an inspiratory tube section  57  and with an expiratory tube section  55 . The measuring arrangement  70  is connected via the suction line  59  to the patient  30  by means of the Y-piece  51 . Suction line  49  suctions off the air, namely, preferably the expired air, near the patient  30 , and this air is then analyzed in measuring arrangement  70 . Among other things, the carbon dioxide content is determined during this analysis and displayed on a display unit  73 . An optical measuring means  75 , which is designed, in conjunction with an operating and analyzing electronic unit  75 , to determine the carbon dioxide gas concentration in the test gas collected, is present in the measuring arrangement  70 . A plurality of elements are present in the respirator  90  to perform anesthesia and respiration of the patient  30  associated therewith. A gas dispensing means  97 , into which gases, such as subsequently oxygen and nitrous oxide, as well as anesthetic gases can be fed from the outside via an access port  11 , is provided. A manual breathing bag  64  with a feed line  62  is provided. The manual breathing bag  64  makes it possible for the anesthesiologist to perform manual respiration and anesthesia of the patient  30 . An anesthetic evaporator  99 , by means of which volatile anesthetics, for example, halothane, can be dispensed into the inspiratory air stream and fed to the patient  30  via the inspiratory tube section  57 , is arranged in the gas path leading to the respiration drive  98 . 
         [0044]    A module  94  is provided, which performs the removal of carbon dioxide by means of a lime absorber, not shown in detail in  FIG. 1 , and which contains an anesthetic gas discharge line, not shown in detail in this  FIG. 1 , and a port  61  for discharging the anesthetic gas into the ambient area or to a gas collection means provided to this end in the hospital infrastructure. 
         [0045]    Furthermore, the respiration drive  98  is designed in this embodiment as a radial compressor with the functionality of a pressure source. An anesthetic evaporator  99 , by means of which volatile anesthetics, for example, halothane, are dispensed into the inspiratory air stream and to the patient  30  via the inspiratory tube section  57 , is arranged in the gas path following the respiration drive  98 . An inspiratory flow sensor  93 , an expiratory flow sensor  95 , a controlled expiratory valve  96  and a pressure sensor  91  arranged on the expiration side are provided as the sensor system and actuator system. 
         [0046]    Furthermore, an operating and actuating unit  900  is provided, which actuates the actuator system  96  and the respiration drive  98  and detects and further processes the signals of the sensor system  91 ,  92 ,  93 ,  95 . The data connections necessary for the detection of the sensor system  91 ,  92 ,  93 ,  95  are not shown in this schematic view according to  FIG. 1 . 
         [0047]      FIGS. 2 through 5  show a time curve of breathing cycles of a patient. The respiration pressure, volume flow and carbon dioxide concentration C CO     2   ) measured by suction by the measuring arrangement are shown in a time synchronicity. 
         [0048]      FIG. 2  shows an embodiment in which no stabilization of the PEEP pressure takes place.  FIG. 3  shows an embodiment in which regulating to the PEEP pressure takes place, wherein the PEEP level is maintained at a constant value during the expiration phase.  FIG. 4  shows an embodiment in which the PEEP pressure is stabilized, wherein the stabilization is actuated according to a dropping desired pressure ramp.  FIG. 5  shows a first variant according to  FIG. 4 , in which the PEEP pressure is stabilized, wherein the stabilization takes place at a constant level, and stabilization takes place according to a dropping desired pressure ramp in a second time period, subsequently to the first time period. 
         [0049]      FIGS. 2 through 5  will be described in more detail now in a general, introductory description of the figures. Furthermore, the features in common and differences in  FIGS. 2 ,  3 ,  4 ,  5  are explained. A time curve of the respiration pressure (P) of the inspiratory volume flow ({dot over (V)} I ), of the expiratory volume flow           e ) and of the carbon dioxide concentration (C CO     2   ) are shown in an arrangement  200 ,  300 ,  400 ,  500  of six diagrams. The three diagrams arranged one under another on the left side show the schematic curve of the respiration pressure (P), of the inspiratory volume flow ({dot over (V)} I ), of the expiratory volume flow           e ) and of the carbon dioxide concentration (C CO     2   ), measured by the measuring arrangement  70  ( FIG. 1 ), with the volume flow suction through the suction line  59  ( FIG. 1 ) by means of pump  77  ( FIG. 1 ) into the measuring arrangement  70  ( FIG. 1 ) not activated. The three diagrams arranged one under the other on the right show the schematic curve of the respiration pressure (P), of the volume flows ({dot over (V)} I ) and           e ) as well as the curve of the carbon dioxide concentration (C CO     2   ), measured in measuring arrangement  70  ( FIG. 1 ) with the volume flow suction through the suction line  59  ( FIG. 1 ) by means of pump  77  ( FIG. 1 ) into the measuring arrangement  70  ( FIG. 1 ) activated. 
         [0050]    The diagrams (P, {dot over (V)}           e , C CO     2   ) arranged on the left side are marked by the use of reference numbers provided with suffix a. The diagrams arranged on the right side are marked by the use of reference numbers provided with suffix b. The reference numbers for the diagrams are selected in this common description of the figures such that assignment to the corresponding figure is indicated by the reference numbers of the diagrams. Elements identical in  FIGS. 2 through 5  are provided with the same reference numbers in all  FIGS. 2 ,  3 ,  4 ,  5 . 
         [0051]    Thus, the reference numbers of the diagrams (P, {dot over (V)}           e , C CO     2   ) begin with  200  for  FIG. 2 , with  300  for  FIG. 3 , with  400  for  FIG. 4  and with  500  for  FIG. 5 . Expiratory pressure curves (P)  201   a  are without activated volume flow suction  59  ( FIG. 1 ) and expiratory pressure curves  201   b  are with activated volume flow suction  59  ( FIG. 1 ) by the measuring arrangement  70  ( FIG. 1 ) in the diagram synopses  200 ,  300 ,  400 ,  500  in the figures. 
         [0052]    Further, the diagram synopses  200 ,  300 ,  400 ,  500  show inspiratory volume flow curves ({dot over (V)} I )  202   a,    302   a,    402   a,    502   a  and expiratory volume flow curves           e )  203   a,    303   a,    403   a,    503   a  without activated volume flow suction  59  ( FIG. 1 ) as well as inspiratory volume flow curves ({dot over (V)} I )  202   b,    302   b,    402   b,    502   b  and expiratory volume flow curves           e )  203   b,    303   b,    403   b,    503   b  with activated volume flow suction  59  ( FIG. 1 ) corresponding in time with the pressure curves (P)  201   a,    201   b,    301   a,    301   b,    401   a,    401   b,    501   a,    501   b.    
         [0053]    Corresponding to the pressure and volume flow curves, but with a time delay due to the volume flow suction, the carbon dioxide concentrations (C CO     2   )  204   a,    304   a,    404   a,    504   a  are shown without activated volume flow suction and the carbon dioxide concentrations (C CO     2   )  204   b,    304   b,    404   b,    504   b  with activated volume flow suction. 
         [0054]    Without activated volume flow suction or without the measuring arrangement  70  ( FIG. 1 ) being connected to the respiratory system  50  ( FIG. 1 ) at the patient  30  ( FIG. 1 ), no carbon dioxide measured signals are present. No curves of the carbon dioxide concentrations (C CO     2   )  204   a,    304   a,    404   a,    504   a  are therefore visible in the diagrams that are shown on the left side in  FIGS. 2 through 5 , marked with suffix a. The diagrams  204   a,    304   a,    404   a,    504   a  are correspondingly shown for the sake of clarity and completeness only. 
         [0055]    The curves  201   a,    201   b,    202   a,    202   b,    203   a,    203   b,    204   a,    204   b  of a technical embodiment of an anesthesia apparatus  90  ( FIG. 1 ) are shown in  FIG. 2  with a measuring arrangement  70  ( FIG. 1 ) in the diagram synopsis  200 , in which the pressure, especially the residual pressure during the expiration phase, is not stabilized. Expiratory pressure levels  101   a,    101   b  are shown in the pressure curves  201   a,    201   b  as an unregulated curve of a  3   a,  of a  3   b  in the form of a desired value or of a set value. The carbon dioxide concentration (C CO     2   ) curves  204  shown as well as the curves of the inspiratory and expiratory volume flows ({dot over (V)}           e )  202   a,    202   b,    203   a,    203   b,  which are shown in this diagram synopsis  200 , are actual values based on measurements. The corresponding curves of the volume flows ({dot over (V)}           e )  202   a,    202   b,    203   a,    203   b  have no influence due to the volume flow suction in this diagram synopsis  200 . The maximum levels  111   a,    111   b  and the basic levels  113   a,    113   b  of the inspiratory volume flow ({dot over (V)} I )  202   a,    202   b  as well as the maximum levels  110   a,    110   b  and the basic levels  112   a,    112   b  of the expiratory volume flow ({dot over (V)} e )  203   a,    203   b  correspond to the respective corresponding curve of the inspiratory and expiratory pressure levels  102   a,    102   b,    103   a,    103   b  in the pressure curves  201   a,    202   b.    
         [0056]    The carbon dioxide concentration (C CO     2   ) likewise corresponds to the pressure curve  202   b  with the basic level  121   b  and the maximum level  120   b,  without the maximum having appreciable discontinuities or signal rounding over the time course of expiration. 
         [0057]      FIG. 3  shows the curves  301   a,    301   b,    302   a,    302   b,    303   a,    303   b,    304   a,    304   b  of a technical embodiment of an anesthesia apparatus  90  ( FIG. 1 ) and of a measuring arrangement  70  ( FIG. 1 ) in the diagram synopsis  300 , in which the pressure is stabilized during the inspiration time and during the expiration time, and especially the positive end-expiratory pressure (PEEP) is stabilized during the expiration phases after a constant curve  104   a,    104   b.  Leaks, such as those occurring due to the activated volume flow suction  59  (Figure) of the measuring arrangement  70  ( FIG. 1 ), as well as leaks in the respiratory system  50  ( FIG. 1 ) and in the gas feed  51 ,  53 ,  54 ,  55 ,  56 ,  57  ( FIG. 1 ) to the patient  30  ( FIG. 1 ) are compensated by this regulation. The representations of the pressure curves  301   a,    301   b,  just as the curves of the volume flows ({dot over (V)}           e )  302   a,    302   b,    303   a,    303   b  and the curves of the carbon dioxide concentrations (C CO     2   )  304   b  represent time curves based on measured values determined by means of the sensor system in this diagram synopsis  300 . The inspiratory and expiratory volume flow curves ({dot over (V)}           e )  303   a,    302   a  with the basic level  112   a,    113   a  and the maximum level  111   a,    110   a  without activation of the volume flow suction to the measuring arrangement  70  ( FIG. 1 ) show no essential differences from the curves  203  according to  FIG. 2 . The expiratory volume flow ({dot over (V)} e )  303   b  with the maximum level  112   b  and the basic level  110   b  shows, with volume flow suction activated, no differences from the expiratory volume flow curve ({dot over (V)} e )  303   a,    112   a,    110   a  without the volume flow suction being activated. The inspiratory volume flow ({dot over (V)} I ) shows, besides the maximum level  111   b  and the basic level  113   b,  a deviation  305   b  at the end of the expiration phase. A quantity of gas is removed from the respiratory system  50  ( FIG. 1 ) by the volume flow suction. Inspiratory gas, which is detected during its flow through the inspiratory flow sensor  91  ( FIG. 1 ) and its curve  302  thus becomes visible as a deviation  305   b  in the form of an additional rate of flow  305   b  at the end of expiration, is fed again due to the adjustment of the PEEP by the respiration drive  98  ( FIG. 1 ), actuated by the operating and analyzing unit  900  ( FIG. 1 ). This additional flow rate  305   b  causes the quantity of gas expired by the patient  30  ( FIG. 1 ) at the Y-piece  51  ( FIG. 1 ) to be mixed with fresh inspiration gas. This mixing causes a reduction of the carbon dioxide concentration (C CO     2   ) at the Y-piece  51  ( FIG. 1 ), because the carbon dioxide is removed from the gas expired by the patient  30  ( FIG. 1 ) due to the removal of carbon dioxide in module  94  ( FIG. 1 ) of the anesthesia apparatus  90  ( FIG. 1 ) and gas free from carbon dioxide is thus delivered to the patient  30  ( FIG. 1 ) for inspiration. This reduction of the carbon dioxide concentration (C CO     2   ) becomes visible in the carbon dioxide concentration (C CO     2   ) curve  304   b  as a drop in the concentration curve  306   b  at the end of expiration from the maximum level  120   b  of the expiratory carbon dioxide concentration (C CO     2   ). 
         [0058]      FIGS. 4 and 5  show the curves  401   a,    401   b,    402   a,    402   b,    403   a,    403   b,    404   a,    404   b,    501   a,    501   b,    502   a,    502   b,    503   a,    503   b,    504   a,    504   b  of a technical embodiment of an anesthesia apparatus  90  ( FIG. 1 ) and of a measuring arrangement  70  ( FIG. 1 ) in the diagram synopses  400 ,  500 , in which the positive end-expiratory pressure (PEEP) is not regulated at a constant value, unlike in the technical embodiment according to  FIG. 3 , but it is regulated in such a manner that the regulated pressure value is stabilized to a higher value at the beginning of expiration than the regulated pressure value at the end of expiration. The difference in the pressure levels between the beginning and the end of the expiration phase is achieved in the technical embodiments according to  FIGS. 4 and 5  by the PEEP pressure being reduced over time during the expiration phase. This reduction of the PEEP may take place, as can be seen in the diagram synopsis  400 , right at the beginning according to a dropping ramp  105   a,    105   b.  However, the reduction may also be implemented according to a curve  106   a,    106   b  according to  FIG. 5  and the diagram synopsis  500  with a constant component  107   a,    107   b  at the beginning of the expiration phase and with a dropping component  108   a,    108   b  beginning during the duration of the expiration phase. 
         [0059]    The shape of the pressure curves  105   a,    106   a,    105   b,    106   b  during the expiration phase according to  FIGS. 4 and 5  is determined in the embodiment of the level at the beginning as well as at the end of the expiration as well as in the embodiment of the dropping component as well as of the constant component of the curve on the basis of the expiratory pressure level  101   a,    101   b.  The expiratory pressure level  101   a,    101   b  indicated by broken lines in  FIGS. 4 and 5  corresponds, on average, to the curves  105   a,    105   b,    106   a,    106   b,  so that there will be no difference for the patient  30  ( FIG. 1 ) compared to a constant PEEP stabilization  104   a,    104   b  according to  FIG. 3  in the pressure balance of the (PEEP) pressure at the patient during each expiration phase. Due to the fact that the pressure level is reduced during expiration, the patient  30  ( FIG. 1 ) is enabled to continue to breathe out towards the end of the expiration until nearly the beginning of the next inspiration, because the pressure level in the lungs  26  ( FIG. 1 ) of the patient  30  ( FIG. 1 ) is likewise lowered according to the curve of the dropping ramp  105   a,    105   b,    106   a,    106   b,    108   a,    108   b.  This additional and also longer-lasting expiration reaches the Y-piece  51  ( FIG. 1 ) and, via the suction line  59  ( FIG. 1 ), the measuring arrangement  70  ( FIG. 1 ). Mixing of expired gas with fresh inspiration gas, adjusted on the basis of the volume flow suction, is thus avoided at the Y-piece  51  ( FIG. 1 ), so that, unlike in the case of a constant stabilization  104   a,    104   b  of the PEEP according to  FIG. 3 , the reduction of the carbon dioxide concentration (C CO     2   ) in the concentration curve  404   b,    504   b  will be recognized in a less significant manner as a drop  406   b  or only insignificantly as a drop  506   b  in case of activated volume flow suction. Thus, as it were, a constant display situation arises for the user concerning the carbon dioxide concentration (C CO     2   ) being displayed over the entire duration of expiration. 
         [0060]    There is a steeper gradient of the dropping component  108   a,    108   b  of the pressure curve in the curve  106   a,    106   b  in  FIG. 5  compared to the curve  105   a,    105   b  in  FIG. 4  due to the presence of the constant component  107   a,    107   b  of the pressure curve at the beginning. This steeper gradient  108   a,    108   b  still enables expiration by the patient also at the end of the expiration phase, so that the reduction at the Y-piece  51  ( FIG. 1 ) with adjusted fresh inspiration gas can take place even less. This is visible from the differences between the dropping curves  406   b,    506   b  between the technical embodiments according to  FIG. 4  and  FIG. 5 . The diagrams of the volume flows ({dot over (V)}           e )  402   b,    403   b,    502   b,    503   b  on the right sides in  FIGS. 4 and 5  show only slight differences from the curves  202   b,    203   b  compared to the technical embodiment with unregulated PEEP according to  FIG. 2 . This arises from the fact that the adjustment of the PEEP causes, just as in  FIG. 3 , at the end of the expiration an inspiratory volume flow ({dot over (V)} I ), which is represented in the form of a deviation or of a forerun  405   b,    505   b  as an additional flow rate besides the maximum levels  111   b  and the basic levels  113   b  of the inspiratory volume flow. With the volume flow suction not activated, the dropping curve  401   a,    501   b  in the diagrams on the left sides of  FIGS. 4 and 5  causes the quantity of gas still being expired by the patient  30  ( FIG. 1 ) at the end of expiration not to be suctioned off at the Y-piece  51  ( FIG. 1 ) of the arrangement  70  ( FIG. 1 ) but to reach via the expiratory tube section  55  ( FIG. 1 ) the anesthesia apparatus  90  ( FIG. 1 ) and to be detected by the expiratory flow sensor  95  ( FIG. 1 ) there. This can be seen as a overrun of the expiratory volume flow  407   a,    507   a  in the curve of the expiratory flow rate  402   a,    502   a  in the diagram synopses  400 ,  500  for the left sides of  FIGS. 4 and 5 . 
         [0061]      FIGS. 6   a,    6   b,    6   c  and  6   d  show technical embodiment variants according to  FIGS. 4 and 5  as well as further technical embodiment variants, in which the regulated positive end-expiratory pressure (PEEP) is reduced at the end of the expiration phase compared to the beginning. 
         [0062]      FIGS. 6   a,    6   b,    6   c,    6   d  show variants of the regulation of the positive end-expiratory pressure (PEEP) according to the pressure curves shown in  FIGS. 4 and 5 . Identical elements in  FIGS. 6   a,    6   b,    6   c,    6   d  are designated by the same reference numbers of the same elements shown in  FIGS. 2 ,  3 ,  4 ,  5 .  FIG. 6   a  shows a schematic pressure curve  601  at the patient according to the pressure curve  401   b  in  FIG. 4 .  FIG. 6   b  shows a schematic pressure curve  602  at the patient according to the pressure curve  501   b  in  FIG. 5 .  FIG. 6   c  shows a pressure curve  603  at the patient in a modified form according to the pressure curve  501   b  in  FIG. 5 .  FIG. 6   d  shows a pressure curve  604  at the patient in a modified form according to the pressure curve  401   b  in  FIG. 4 . 
         [0063]    The pressure curves  601 ,  602 ,  603 ,  604  in  FIGS. 6   a,    6   b,    6   c,    6   d  may be further adapted. In particular, combinations of the modified forms  603 ,  604  with one another and/or with the pressure curves  601 ,  602  are also covered in the sense of the present invention. 
         [0064]      FIGS. 6   a,    6   b,    6   c,    6   d  will be explained now in more detail in a common description of the figures in terms of the features they have in common and with illustration of the differences from each other in the technical embodiments of the regulation of the positive end-expiratory pressure (PEEP). 
         [0065]    Identical reference numbers are used for identical elements in  FIGS. 6   a,    6   b,    6   c,    6   d.  The suffixes a, b, c, d used additionally at/in the reference numbers are used to make it possible to distinguish basically identical reference numbers and features in  FIGS. 6   a,    6   b,    6   c,    6   d.  The use of suffix a pertains to elements of  FIG. 6   a.  The use of suffix b pertains to elements of  FIG. 6   b.  The use of suffix c pertains to elements of  FIG. 6   c.  The use of suffix d pertains to elements of  FIG. 6   d.  Pressure curves beginning at the end of an inspiration with a first component  1  T i1    660  with an inspiratory pressure level P i    620 , with an expiration time T e    650  following same and with a component  2  T i2    670  of the inspiration following next with the inspiratory pressure level P i    620  are plotted on the abscissa (x)  605  over time  610  in the pressure curves  601 ,  602 ,  603 ,  604  shown in  FIGS. 6   a,    6   b,    6   c,    6   d.    
         [0066]    Expiratory, dropping pressure curves  615   a  ( FIG. 6   a ),  615   b  ( FIG. 6   b ),  615   c  ( FIGS. 6   c ) and  615   d  ( FIG. 6   d ) are shown in the expiration time T e    650  shown. The schematic pressure curves  601 ,  602 ,  603 ,  604  are scaled as pressure  611  on an ordinate (y)  609 . Ordinate  609  is divided by a separation sign  608  into two sections. The first section of ordinate  606  scales the inspiratory pressure level  620  in the expiration times T i1    660  and T i2    670 . The second section of ordinate  607  is adapted in a different scaling of the positive end-expiratory pressure (PEEP) during the expiration time T e    650  in order to make it possible to represent the expiratory, dropping pressure curves in a graphic form in a suitable manner. The values of the inspiratory pressure levels  620  are selected to the identical in  FIGS. 6   a,    6   b,    6   c,    6   d.  The scaling of ordinate  609  and of the sections of the ordinates  606 ,  607  are selected to be identical and represented as being identical in  FIGS. 6   a,    6   b,    6   c,    6   d.  A zero level  651  is shown in  FIGS. 6   a,    6   b,    6   c,    6   d  as a reference for scaling the ordinate  609 . Furthermore, a mean value of the positive end-expiratory pressure  PEEP   612   a,    612   b,    612   c,    612   d  is shown with reference to the zero level  651  in the form of a broken line. The starting values P e1    613   a,    613   b,    613   c,    613   d  and the final values P e2    614   a,    614   b,    614   c,    614   d  of the expiratory pressure at the beginning and at the end of the expiration time T e    650  are derived and determined from this mean value (  PEEP )  612  of the positive end-expiratory pressure. This determination of P e1    613   a,    613   b,    613   c,    613   d  and of P e2    614   a,    614   b,    614   c,    614   d  is performed in the technical embodiments according to  FIGS. 6   a,    6   b,    6   c,    6   d  on the basis of the predetermined mean value  PEEP   612 , the expiration time T e    650  as well as of the respective curve describing the pressure stabilization in  FIGS. 6   a,    6   b,    6   c,    6   d,  respectively. The mean value  PEEP   612  of the end-expiratory pressure as well as the expiration time T e    650  and the inspiratory pressure level P i    620  will be obtained as different values for different types of patients, as it is explained in the description in Table 1 and in Table 2. 
         [0067]    The pressure curve of the PEEP is shown in  FIG. 6   a  over the expiration time T e    650  as a linear, dropping ramp  615   a,  which is dropping over the entire expiration time T e    650 . 
         [0068]    In  FIG. 6   b,  the pressure curve of PEEP over the expiration time T e    650  is a two-part function curve  615   b  beginning with a time period of the curve with constant pressure level  618   b  and with a subsequent time period of the curve with dropping pressure  619   b.    
         [0069]    In  FIG. 6   c,  the pressure curve of PEEP over the expiration time T e    650  as a modified form of the two-part function curve  615   b  according to  FIG. 6   b,  and a constant time period and a dropping time period pass continuously over into each other after a progressively dropping function curve  615   c.  Such a progressively dropping function curve  615   c  can be formed in a suitable manner preferably by means of potential functions, exponential or logarithmic functions, as well as broken rational functions or in a special manner by means of combinations of potential functions, exponential, logarithmic or broken rational functions. A progressive drop of PEEP towards the end of the expiration phase causes the patient  30  ( FIG. 1 ) to let expired, carbon dioxide-containing air flow to the Y-piece  53  ( FIG. 1 ) over the entire expiration. Thus, there is no mixing with fresh inspiration gas at the Y-piece  53  ( FIG. 1 ), so that there will be no drop in the carbon dioxide concentration (C CO     2   ), unlike in case of stabilization to an unchanging, constant PEEP, as is shown in  FIG. 3 . The progressive drop  615   c  rather leads to the effect that there is no essential drop in the carbon dioxide concentration (C CO     2   ) at the end of expiration, and this drop is comparable to the drop as it is shown in  FIG. 5  in the expiratory CO 2  concentration curve  504   b  ( FIG. 5 ). 
         [0070]      FIG. 6   d  shows a pressure curve according to  FIG. 6   a  in a modified form. The dropping curve  615   d  of the expiratory pressure during the expiration time T e    650  is a discontinuous curve. This means that the drop of PEEP during expiration is embodied as a discontinuous curve  615   d  dropping steps due to the pressure regulation in the operating and analyzing unit  900  ( FIG. 1 ) rather than as a continuous function curve. Such a stepped or also stepwise lowering of PEEP arises, for example, from the digitization and/or quantification in digital and/or binary computing units (microcontrollers, processors, digital signal processors) on the basis of the bit resolutions used in these systems. 
         [0071]    The mean PEEP values (  PEEP )  612   a,    612   b,    612   c,    612   d  are selected as a first preset value and the duration of the expiration phase T e    650  is selected as a second preset value in  FIGS. 6   a,    6   b,    6   c,    6   d.  The starting value (P e1 ) of the expiratory pressure  613   a,    613   b,    613   c,    613   d  and the final value of the expiratory pressure (P e2 )  614   a,    614   b,    614   c,    614   d  are set in conjunction with the respective selected shape of the pressure drop curve  615   a,    615   b,    615   c,    615   d.  This setting is performed in  FIGS. 6   a,    6   b,    6   c,    6   d  such that the starting values (P e1 )  613   a,    613   b,    613   c,    613   d  and the final values (P e2 )  614   a,    614   b,    614   c,    614   d  are selected in conjunction with the curve  615   a,    615   b,    615   c,    615   d  such that a first area  681   a,    681   b,    681   c,    681   d,  defined between the mean PEEP (  PEEP )  612   a,    612   b,    612   c,    612   d  and the curve  615   a,    615   b,    615   c,    615   d  above the mean PEEP (  PEEP )  612   a,    612   b,    612   c,    612   d  and a second area  682   a,    682   b,    682   c,    682   d,  defined between the mean PEEP (  PEEP )  612   a,    612   b,    612   c,    612   d  and the curve  615   a,    615   b,    615   c,    615   d  below the mean PEEP (  PEEP )  612   a,    612   b,    612   c,    612   d  agree in terms of superficial contents. Embodying a dropping pressure ramp according to  FIGS. 6   a,    6   b,    6   c,    6   d,  a positive end-expiratory pressure (PEEP) is obtained for the patient  30  ( FIG. 1 ) due to this setting, and this positive end-expiratory pressure corresponds, on average, to the same positive end-expiratory pressure (PEEP) as in case of constant stabilization of the PEEP over the expiration phase, as is shown in  FIG. 2 , with the advantage that the measured carbon dioxide concentration (C CO     2   ) does not drop towards the end of the expiration phase or it does not do so substantially. 
         [0072]    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.