METHOD FOR OPERATING A VENTILATOR FOR ARTIFICIAL VENTILATION OF A PATIENT, AND SUCH A VENTILATOR

Abstract

A method for operating a ventilator for artificial ventilation of a patient, comprising: initial recording of at least one patient-specific physiological parameter, initial setting of at least one technical respiration parameter, and ventilation of the patient based on the technical respiration parameter. The technical respiration parameter corresponds to at least one of respiratory minute volume (VE), tidal volume (V.sub.T), respiratory rate (RR), positive end-expiratory pressure (PEEP), or inspiratory oxygen concentration (FiO.sub.2) made available by the ventilator. A repeating measurement of the parameter is carried out by the ventilator at time intervals, and an adaptation of the parameter is effected by the ventilator based on said repeating measurement. A ventilator for artificial ventilation of a patient is also proposed.

Claims

1. A method for operating a ventilator for artificial ventilation of a patient, wherein the method comprises: initial recording of at least one patient-specific physiological parameter, initial setting of at least one technical respiration parameter, and ventilation of the patient based on the technical respiration parameter, wherein the at least one technical respiration parameter corresponds to at least one of the respiration parameters which comprise respiratory minute volume (VE), tidal volume (V.sub.T), respiratory rate (RR), positive end-expiratory pressure (PEEP), or an inspiratory oxygen concentration (FiO.sub.2) made available by the ventilator, wherein a repeating measurement of the at least one patient-specific physiological parameter is carried out by the ventilator at time intervals, and wherein an adaptation of the at least one technical respiratory parameter is effected by the ventilator on the basis of the repeating measurement of the patient-specific physiological parameter.

2. The method of claim 1, wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters which comprise airway dead space (V.sub.Daw), alveolar dead space (V.sub.Dalv) or physiological dead space (V.sub.Dphys) of the patient.

3. The method of claim 1, wherein the repeating measurement of the at least one patient-specific physiological parameter is carried out after each breath of the patient.

4. The method of claim 1, wherein the repeating measurement of the at least one patient-specific physiological parameter is effected by capnography by the ventilator, and wherein the at least one patient-specific physiological parameter corresponds to at least one parameter directly representing an CO.sub.2gas exchange in lungs of the patient.

5. The method of claim 1, wherein the repeating measurement of the at least one patient-specific physiological parameter is effected by oxygraphy by the ventilator, and wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters comprising alveolar O.sub.2 partial pressure (PCO.sub.2) and/or volume of oxygen taken up by the patient in one breath (VO.sub.2).

6. The method of claim 1, wherein the at least one patient-specific physiological parameter corresponds to at least the parameter arterial CO.sub.2 partial pressure (PaCO.sub.2), the arterial CO.sub.2 partial pressure (PaCO.sub.2) being approximated via non-invasively measured patient-specific physiological parameters.

7. The method of claim 1, wherein the repeating measurement of the at least one patient-specific physiological parameter is effected by pulse oximetry, and wherein the at least one patient-specific physiological parameter corresponds to at least the parameter arterial oxygen saturation of blood of the patient (SpO.sub.2).

8. The method of claim 1, wherein, as the at least one patient-specific physiological parameter, the parameter volumetric blood flow of an intrapulmonary right-to-left shunt of the patient (PBF.sub.SHUNT) is determined from the parameters which comprise alveolar oxygen concentration, amount of oxygen taken up by the patient in one breath and/or arterial oxygen saturation of blood of the patient (SpO.sub.2).

9. The method of claim 1, wherein a recruiting maneuver is carried out at a start of an artificial ventilation, wherein lung overdistension is achieved by initial provision of an increased ventilation pressure, and then a ventilation pressure is reduced and a PEEP titration is carried out.

10. The method of claim 1, wherein a ventilation pressure amplitude is permanently monitored during artificial ventilation, an alarm being triggered if a preset maximum ventilation pressure amplitude is exceeded.

11. The method of claim 1, wherein based on a recording of at least one patient-specific physiological parameter, proportions (in %) and/or absolute values (in ml) for regions of lungs/a lung filling are determined which, relative to at least the one patient-specific physiological parameter, represent anatomic dead space and/or represent alveolar dead space volume and/or represent functional alveoli and/or represent a shunt and/or represent VtCO2, the regions of the lungs being shown differently in a graph (by coloring or hatching) according to their proportions or absolute values.

12. A ventilator for artificial ventilation of a patient, which ventilator comprises: a measuring device configured to record at least one patient-specific physiological parameter, a control device configured to set at least one technical respiration parameter, wherein the ventilation of a patient takes place on the basis of the technical respiration parameter, wherein the at least one technical respiration parameter corresponds to at least one of the respiration parameters which comprise respiratory minute volume (VE), tidal volume (V.sub.T), respiratory rate (RR), positive end-expiratory pressure (PEEP), or the inspiratory oxygen concentration (FiO.sub.2) made available by the ventilator, and a regulator unit, which is in communication with the measuring device and with the control device, wherein the measuring device is configured in such a way that it carries out a repeating measurement of the at least one patient-specific physiological parameter at time intervals, and wherein the regulator unit is configured in such a way that it carries out an adaptation of the at least one technical respiration parameter on the basis of the repeating measurement of the patient-specific physiological parameter.

13. The ventilator of claim 12, wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters which comprise airway dead space (V.sub.Daw), alveolar dead space (V.sub.Dalv) or physiological dead space (V.sub.Dphys) of the patient.

14. The ventilator of claim 12, wherein the measuring device further is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter after each breath taken by the patient.

15. The ventilator of claim 12, wherein the measuring device is designed as a capnograph and is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter by capnography, and wherein the at least one patient-specific physiological parameter corresponds to at least one parameter directly representing a CO.sub.2 gas exchange in lungs of the patient.

16. The ventilator of claim 12, wherein the measuring device is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter by oxygraphy, and wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters which comprise alveolar O.sub.2 partial pressure (PCO.sub.2) and/or volume of oxygen taken up by the patient in one breath (VO.sub.2).

17. The ventilator of claim 12, wherein the at least one patient-specific physiological parameter corresponds to at least the parameter arterial CO.sub.2 partial pressure (PaCO.sub.2), the measuring device being configured in such a way that it approximates the arterial CO.sub.2 partial pressure (PaCO.sub.2) via non-invasively measured patient-specific physiological parameters.

18. The ventilator of claim 12, wherein the measuring device is designed as a pulse oximeter and is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter by pulse oximetry, the at least one patient-specific physiological parameter corresponding at least to the parameter arterial oxygen saturation of blood of the patient (SpO.sub.2).

19. The ventilator of claim 12, wherein the measuring device is configured in such a way that, as the at least one patient-specific physiological parameter, it determines the parameter volumetric blood flow of an intrapulmonary right-to-left shunt of the patient (PBF.sub.SHUNT) from the parameters comprising alveolar oxygen concentration, amount of oxygen taken up by the patient in one breath and/or arterial oxygen saturation of the blood of the patient (SpO.sub.2).

20. The ventilator of claim 12, wherein the control device is configured in such a way that it carries out a recruiting maneuver at a start of the artificial ventilation, wherein lung overdistension is achieved by initial provision of an increased ventilation pressure, and then a ventilation pressure is reduced and a PEEP titration is carried out.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Preferred embodiments of the invention are described by way of example with reference to the accompanying figures, in which

[0059] FIG. 1 shows an exemplary diagram on the basis of which the right-to-left shunt in a patient can be determined;

[0060] FIG. 2 shows a typical diagram of volumetric capnography, and the most important values that can be derived therefrom for the artificial ventilation; and

[0061] FIG. 3 shows two diagrams representing time-based capnography (left) and volume-based capnography (right).

[0062] FIG. 4 shows two diagrams representing time-based capnography (left) and volume-based capnography (right), with the dead space proportions.

[0063] FIG. 5 shows monitoring of the alveolar ventilation on the basis of volumetric capnography.

[0064] FIG. 6 shows a view on the display of a ventilator.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0065] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description in combination with the drawings making apparent to those of skill in the art how the several forms of the present invention may be embodied in practice.

[0066] Two examples of curves 1, 2 are shown in FIG. 1, wherein the value pairs have been labeled with squares on curve 1 and with circles on curve 2. Measured oxygen saturation values (SpO.sub.2 values) of an artificially ventilated patient are plotted on the y axis for different inspiratory oxygen concentrations (FiO.sub.2) that have been made available by the ventilator, which are plotted on the x axis.

[0067] In order to determine the right-to-left shunt in the lungs, the inspiratory oxygen concentration FiO.sub.2 is lowered in stages from high concentrations to the ambient air level, and the resulting corresponding SpO.sub.2 values are determined via the measuring device of the proposed ventilator. These points are then connected to one another to form a curve 1 or 2, and their profile is compared with the iso-shunt curve determined beforehand on the basis of physiological relationships, and then the matching shunt value is read off.

[0068] These iso-shunt curves are plotted as fine lines with associated shunt values in FIG. 1 in the diagram. The approximated shunt values can be read off from the correspondence of the measured curves with the iso-shunt curves. Here, curve 1 corresponds to a right-to-left shunt of ca. 24%, while curve 2 corresponds to a right-to-left shunt of less than 10%.

[0069] FIG. 2 shows a diagram of volume-based capnography and of the most important parameters thereof. Such a diagram can be integrated in the proposed ventilator and, in addition, the medical personnel providing the treatment can be shown this diagram on a display unit, for example a display screen.

[0070] In the diagram, the measured CO.sub.2 partial pressure PCO.sub.2 of the exhaled air is plotted in mmHg on the y axis, and the tidal volume V.sub.T is plotted in ml on the x axis. Various patient-specific physiological parameters important for ventilation can be read off from the indicated curve 3.

[0071] Examples of these are the following clinically important CO.sub.2 partial pressures: PETCO.sub.2 as end-tidal CO.sub.2 partial pressure, PACO.sub.2 as mean alveolar CO2 partial pressure, and PĒCO.sub.2 as the mixed expiratory CO2 partial pressure. The mixed expiratory CO.sub.2 partial pressure PĒCO.sub.2 derives from the dilution effect that arises as a result of the physiological dead space V.sub.Dphys. These are all patient-specific physiological parameters that can generally be measured by the measuring device of the ventilator and can then serve as a basis for the adaptation of the technical respiration parameters.

[0072] Further patient-specific physiological parameters are PaCO.sub.2 as the CO.sub.2 partial pressure in the arterial blood, which is analyzed by means of blood sampling and appears as a dotted line at the top in the capnogram. The mathematical reversal point of the capnogram—the interface between airways and alveoli—is the boundary between the airway dead space V.sub.Daw and the alveolar tidal volume V.sub.Talv.

[0073] The dead space volume is generally attributable to the fact that, in each respiratory cycle, a proportion of the tidal volume V.sub.T remains in the air-conducting airways and does not therefore reach the alveolar compartment. This proportion is called airway dead space V.sub.Daw. In artificially ventilated patients, there is often an additional instrumental dead space V.sub.Dinst, which is caused by components of the ventilator, such as connectors, angle pieces or humidifying filters or micobe filters, which are placed between the Y-piece and the endotracheal tube in the ventilator. In addition to all this, there is also what is known as the alveolar dead space V.sub.Dalv. This results from alveoli which, although supplied with air, are not perfused. Accordingly, these alveoli also do not take part in the gas exchange. The airway dead space V.sub.Daw and the alveolar dead space V.sub.Dalv together determine the total dead space V.sub.D, which is also referred to as the physiological dead space V.sub.Dphys.

[0074] The total dead space V.sub.D can be determined by means of volumetric capnography. For this purpose, use is made of the Fowler concept, which is based on the Bohr formula. Fowler postulated that the boundary between the convective gas transport in the air-conducting airways (dead space) and the diffusive gas transport is formed by the interface between airways and alveoli, which interface is in turn represented by the reversal point of the CO.sub.2 profile in the capnogram, cf. FIG. 2. This approach allows the airway dead space V.sub.Daw of each breath to be determined repetitively and non-invasively.

[0075] The Bohr formula is a mass balance equation in which the proportion of the tidal volume V.sub.T that does not contain CO.sub.2 is calculated as follows:

V.sub.Dphys/V.sub.T=V.sub.D/V.sub.T=(PACO.sub.2−PĒCO.sub.2)/(PACO.sub.2−PICO.sub.2)

where PICO.sub.2 is the inspired CO.sub.2 partial pressure at which, under normal circumstances, a value of zero is assumed, since the fresh gas ought not to contain CO.sub.2. However, for adequate calculation of the dead space, this value always has to be taken into account, because some of the CO.sub.2 rebreathing stems from the Y-piece of the ventilator and from an additional instrumental dead space V.sub.Dinst. Finally, the alveolar dead space V.sub.Dalv is calculated by subtracting the airway dead space V.sub.Daw from the physiological dead space V.sub.Dphys.

[0076] The dead space V.sub.D or V.sub.Dphys can be expressed as part of the minute ventilation in l/min or as an absolute value of one breath, as physiological dead space V.sub.Dphys in ml, or else as a ratio to the tidal volume V.sub.D/V.sub.T. The latter ratio is most suitable, since the dead space V.sub.D or V.sub.Dphys is greatly influenced by the extent of the tidal volume V.sub.T. The dead space ratios, standardized to the expired volume, permit comparison between persons of different weight, who are ventilated with different tidal volumes V.sub.T.

[0077] For the clinical applications, it is important to know the physiological dead space values V.sub.Dphys. In healthy and young, spontaneously breathing patients, the ratio of physiological dead space V.sub.Dphys to tidal volume V.sub.T (V.sub.Dphys/V.sub.T) is approximately 20-25%, divided into the ratios airway dead space V.sub.Daw to tidal volume V.sub.T (V.sub.Daw/V.sub.T) with ca. 15-20% and alveolar dead space V.sub.Dalv to tidal volume V.sub.T (V.sub.Dalv/V.sub.T) with about 5-9%.

[0078] In patients with healthy lungs, machine ventilation increases the ratio physiological dead space V.sub.Dphys to tidal volume V.sub.T (V.sub.Dphys/V.sub.T) to 30-40%, while this value in intensive-care patients is over 40%. In patients with chronic pulmonary diseases, there are increased physiological dead spaces V.sub.Dphys of more than 50%, whereas the airway dead space V.sub.Daw and the alveolar dead space V.sub.Dalv may be increased by two to three times compared to the normal value.

[0079] In an article by Enghoff (Enghoff H. Volum inefficax. Bernerkungen zur Frage des schädlichen Raumes. Upsala Läk Fören Förch 1938; 44: 191-218), the Bohr formula was modified by replacing the alveolar CO.sub.2 partial pressure PACO.sub.2 with the arterial CO.sub.2 partial pressure PaCO.sub.2, because the alveolar CO.sub.2 partial pressure PACO.sub.2 was not measurable at the bedside. However, this invasive and intermittent calculation method, using blood gas analysis, systematically overestimates the dead space V.sub.D, because the value of the arterial CO.sub.2 partial pressure PaCO.sub.2 is normally always higher than the alveolar CO.sub.2 partial pressure PACO.sub.2 influenced by the dead space V.sub.D and the shunt effect. However, with the method proposed according to the invention, the Bohr formula can in practice be used completely non-invasively, since the determination of the alveolar CO.sub.2 partial pressure PACO.sub.2 and the mixed-expiratory CO.sub.2 partial pressure PĒCO.sub.2 is technically possible from the volumeteric capnogram and is integrated in the ventilator proposed according to the invention.

[0080] With the volumetric capnography tool presented here, the dead space proportion of the tidal volume and thus the efficiency of the ventilation can be determined at the bedside, wherein an additional arterial blood gas analysis can also deliver an additional and reliable estimate of the shunt.

[0081] On the basis of its voltage-based values, the capnography delivers information on the CO.sub.2 diffusion in an entirely non-invasive manner. The end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture PETCO.sub.2 is the best known parameter of capnography. It represents the CO.sub.2 partial pressure in peripheral lung portions, or in those with a long time constant, where emptying into the large airways takes place after a delay. By contrast, the alveolar CO.sub.2 partial pressure PACO.sub.2 represents all lung units with different time constants. For many years it was assumed that this value could not be measured at the bedside. With the method proposed according to the invention, the alveolar CO.sub.2 partial pressure PACO.sub.2 can be determined precisely as the midpoint of the rise from the last phase of the capnogram curve shown in FIG. 2. The reason for this is that such a point has to represent the averaged CO.sub.2 value in all alveoli, since this last phase is determined only by the gases in the alveoli. In this way, by means of the method proposed according to the invention, alveolar ventilation and dead spaces can advantageously be determined breath by breath and non-invasively.

[0082] The alveolar CO.sub.2 partial pressure PACO.sub.2 can now likewise be used, in addition to the end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture PETCO.sub.2, for the approximation of the arterial CO.sub.2 partial pressure PaCO.sub.2. However, it must always be clear that, ultimately, the clinically important arterial CO.sub.2 partial pressure PaCO.sub.2 cannot be replaced either by the end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture PETCO.sub.2 or by the alveolar CO.sub.2 partial pressure PACO.sub.2: the reason being shunt and dead space effects. Both of these cause the arterial CO.sub.2 partial pressure PaCO.sub.2 to be usually higher than the alveolar CO.sub.2 partial pressure PACO.sub.2 and end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture PETCO.sub.2. On account of the presence of an anatomical shunt and dead space, this even applies to young persons with healthy lungs. Therefore, in critical situations, particularly when important changes to the CO.sub.2 kinetics are observed or suspected, a complementary blood gas analysis should be carried out.

[0083] However, according to the proposed method, the arterial CO.sub.2 partial pressure PaCO.sub.2 can be further approximated by means of capnography. This can be achieved by determining the arterial to end-tidal CO.sub.2 gradient Pa-ETCO.sub.2 or else the arterial to alveolar CO.sub.2 difference Pa-ACO.sub.2. By means of capnography, it is possible to approximate the arterial CO.sub.2 partial pressure PaCO.sub.2 when a difference calculated in this way is added to the non-invasive values end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture PETCO.sub.2 or alveolar CO.sub.2 partial pressure PACO.sub.2.

[0084] The normal difference value for the arterial to end-tidal CO.sub.2 gradient Pa-ETCO.sub.2 is ≤5 mmHg, and the normal value for the arterial to alveolar CO.sub.2 difference Pa-ACO.sub.2 is ˜5-8 mmHg. Here, the arterial to alveolar CO.sub.2 difference Pa-ACO.sub.2 is the more suitable index, since it represents the averaged value of the whole alveolar compartment, while the arterial CO.sub.2 partial pressure PaCO.sub.2 does this with reference to the vessels. The arterial to alveolar CO.sub.2 difference Pa-ACO.sub.2 is therefore suitable for estimating the diffusion at the alveolar-capillary membrane.

[0085] FIG. 3 shows time-based capnography on the left-hand side and volume-based capnography on the right-hand side. Analogously to the standard capnogram, the volumetric capnogram on the right can be divided into the following three phases: phase I represents the first part of the expiration in which there is no CO.sub.2. In this ventilation phase I, approximately 10-12% of the tidal volume V.sub.T is made available. Phase II shows a rapid rise in CO.sub.2 during the expiration. In this ventilation phase II, approximately the next 15-18% of the tidal volume V.sub.T are made available. Finally, phase III is reached, in which the proportion of the tidal volume V.sub.T determined only by the gases coming from the alveoli makes up the remaining 70-75% of the tidal volume V.sub.T.

[0086] The volumetric capnography or the capnogram can be characterized more closely by the gradient of two intersecting straight lines. One straight line is the gradient of phase II and is characterized by the characteristic value S.sub.II. The normal value of S.sub.II is 0.36-0.40 mmHg/ml and is determined by the different CO.sub.2 emptying rates from different lung units into the large airways. The other straight line is the gradient of phase III and is characterized by the characteristic value S.sub.III. The normal value of S.sub.III is 0.007-0.017 mmHg/ml, wherein S.sub.III is determined mainly by the distribution of aeration and perfusion in the lungs. The angle alpha is the angle formed at the intersection of the straight lines S.sub.II and S.sub.III, wherein the normal value for the angle alpha is 150-160°.

[0087] The area under the curve is the most important parameter. The area represents the amount of CO.sub.2 that is eliminated in one breath and is labeled with the sign VTCO.sub.2,br. This value is dependent especially on patient-specific factors and the extent of the tidal volume V.sub.T. A typical value of the tidal volume V.sub.T in an adult is ca. 10-30 ml.

[0088] A further differentiation relates to values based on partial pressure; these are important parameters of the expiratory CO.sub.2 that are used for the calculation of clinical variables, e.g. the dead space V.sub.D. The end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture PETCO.sub.2 has normal values which, in the example shown here, are ca. 33-37 mmHg. PACO.sub.2 is the mean alveolar CO.sub.2 partial pressure which, on account of the positive gradient in phase III with values of ca. 30-35 mmHg, is generally lower than the corresponding end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture PETCO.sub.2. PĒCO.sub.2 is the mixed-expiratory CO.sub.2 partial pressure, which results from the dilution effect occasioned by the physiological dead space V.sub.Dphys, wherein the mixed-expiratory CO.sub.2 partial pressure PĒCO.sub.2 assumes values of ca. 18-24 mmHg.

[0089] The mathematical reversal point (i.e. the point at which the curvature behavior of the capnogram curve changes) represents the mean value of the stationary interfaces between the convective and the diffusive CO2 transport in the lungs. At the end of the inspiration, it is anatomically located near the respiratory bronchioles. This interface between airways and alveoli determines the transfer between the airways and the alveolar compartments.

[0090] With each breath, the capnography based on time and the capnography based on time and volume thus both provide, in a non-invasive manner, complementary bedside information concerning all the important functions of the body that take part in the CO.sub.2 kinetics.

[0091] With the proposed method and the proposed ventilator, artificial ventilation aids are now made available by means of which the artificial ventilation can proceed safely, in particular with the aid of the measurement methods of capnography. Capnography offers advantageous monitoring for machine-ventilated patients. Time-based capnography describes the expiratory CO.sub.2 in its chronological sequence and provides real-time information concerning the puffs administered and also qualitative information concerning the CO.sub.2 kinetics of the organism. By contrast, volume-based capnography provides clinically relevant volumetric data on the CO.sub.2 kinetics. Both methods of capnography are available at the bedside, are non-invasive and provide complementary, clinically relevant information. Volume-based capnography represents a major advance over todays standard measurement of the mechanism of respiration, because it is capable of providing characteristic values of the gas exchange. Volume-based capnography not only measures the CO.sub.2 load to be eliminated by the ventilation, it also describes the efficiency and the hemodynamic effects of each breathing mode and the corresponding respiration settings. Volume-based capnography, integrated in the proposed ventilator, thus opens up a new dimension in the monitoring of ventilation and hemodynamics.

[0092] FIG. 4, analogously to FIG. 3, shows the time-based capnography on the left and the volume-based capnography on the right, with the dead spaces indicated on the right.

[0093] FIG. 5 shows the profile of different patient-specific physiological parameters in the monitoring of alveolar ventilation on the basis of volumetric capnography. It shows the change of the alveolar ventilation (VA), in the case of a hemodynamically stable patient, by reduction of the respiratory rate (RR) from 15 to 10 breaths per minute (1), by increase (2) and reduction (3) of the tidal volume (VT) during controlled ventilation. The elimination of carbon dioxide (VCO.sub.2) and the alveolar CO.sub.2 partial pressures (PACO.sub.2) behave in opposite senses. The arterial CO.sub.2 partial pressure (PaCO.sub.2) is shown over the alveolar PACO.sub.2 (upper line in C).

[0094] Not all parts of the airway—from the mouth and nostrils to the alveoli—actually take part in the gas exchange. In order to assess the effectiveness of the ventilation and, if appropriate, to optimize it, information concerning the proportion of the “effective” alveolar ventilation is very helpful. On account of its high degree of solubility, and therefore its very rapid kinetics, CO.sub.2 is an ideal indicator for alveolar ventilation (VA).sup.2. Therefore, the measurement and graphic representation of the CO.sub.2 partial pressure measured in the exhaled gas mixture (PETCO.sub.2) in the form of the capnography curve is recommended for the continuous monitoring of ventilation.sup.1,2. Examples for the qualitative assessment of the ventilation by means of capnography are: disconnection, apnea, exclusion of incorrect intubation, obstruction, exclusion of patient-ventilator asynchrony, and much more besides. PETCO.sub.2 is also used as a quantitative measurement for adjusting the ventilation. In the case of stable hemodynamics and a constant metabolism, a high PETCO.sub.2 is an indicator of hypoventilation and a low PETCO.sub.2 is an indicator of hyperventilation. Both in practice entail an adaptation of the respiratory minute volume (VE) on the ventilator. Since VE is the product of tidal volume and respiratory rate, it is recommended to modulate these two components for this purpose. In principle, low tidal volumes (VT) are nowadays sought in order, by means of lung-protective ventilation, to avoid volutrauma, biotrauma and barotrauma.sup.3. What has to be taken into consideration in particular, however, is the fact that, in addition to the alveoli that participate in the gas exchange, dead spaces are also aerated on each breath. The proportion of this dead-space aeration critically influences the efficiency of the ventilation.sup.2,4,52. For respiratory minute volume, alveolar ventilation (VA) and dead-space ventilation (VD), the following simple formula applies:

VE=VA+VD

[0095] VE is thus composed of an effective part, in which the gas is in contact with the lung capillaries and thus takes part in the gas exchange (alveolar ventilation=VA), and an ineffective part, which does not take part in the gas exchange (dead space=VD).sup.2. Thus, VA and its proportion of VE are a measure of the efficiency of respiration and, particularly in someone with limited respiration, VA and VD are important characteristic values for optimization of the ventilation setting. Accordingly, VA is calculated as:

VA=VE−VD

[0096] Picture 1 shows the importance of VA in the elimination of CO.sub.2 in a hemodynamically stable, anesthetized patient. Changes of respiratory rate and VT-induced changes of VA influence the CO.sub.2 partial pressures and CO.sub.2 elimination (VCO.sub.2) in opposite ways. The higher VCO.sub.2, with elevated VA, reduces the partial pressures on both sides of the alveolar-capillary membrane, which leads to hypocapnia. Conversely, the lower VA results in a lower CO.sub.2 elimination and, consequently, hypercapnia.

[0097] FIG. 6 shows a view on the display of the ventilator. Based on the recording of at least one patient-specific physiological parameter, proportions (in %) and/or absolute values (in ml) for regions of the lungs/the lung filling were determined here which, relative to at least the one patient-specific physiological parameter, represent anatomic dead space and/or represent alveolar dead space volume and/or represent functional alveoli and/or represent a shunt and/or represent VtCO2. The regions of the lungs are shown differently in a graph, by coloring or hatching, according to their proportions or absolute values and are preferably displayed in a graphic representation of the lungs.

[0098] To sum up, the present invention provides: [0099] 1. A method for operating a ventilator for artificial ventilation of a patient, which method comprises: [0100] initial recording of at least one patient-specific physiological parameter, [0101] initial setting of at least one technical respiration parameter, and [0102] ventilation of the patient based on the technical respiration parameter, [0103] wherein the at least one technical respiration parameter corresponds to at least one of the respiration parameters which comprise respiratory minute volume (VE), tidal volume (V.sub.T), respiratory rate (RR), positive end-expiratory pressure (PEEP), or an inspiratory oxygen concentration (FiO.sub.2) made available by the ventilator, [0104] wherein a repeating measurement of the at least one patient-specific physiological parameter is carried out by the ventilator at time intervals, and [0105] wherein an adaptation of the at least one technical respiratory parameter is effected by the ventilator on the basis of the repeating measurement of the patient-specific physiological parameter. [0106] 2. The method of item 1, wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters which comprise airway dead space (V.sub.Daw), alveolar dead space (V.sub.Dalv) or physiological dead space (V.sub.Dphys) of the patient. [0107] 3. The method of any one of items 1 or 2, wherein the repeating measurement of the at least one patient-specific physiological parameter is carried out after each breath of the patient. [0108] 4. The method of any one of items 1 through 3, wherein the repeating measurement of the at least one patient-specific physiological parameter is effected by means of capnography, preferably volumetric capnography, by the ventilator, and wherein the at least one patient-specific physiological parameter corresponds to at least one parameter directly representing the CO.sub.2 gas exchange in the lungs of the patient, preferably at least one of the parameters comprising end-expiratory CO.sub.2 partial pressure in the exhaled gas mixture (PETCO.sub.2), alveolar CO.sub.2 partial pressure (PACO.sub.2), or a volume of CO.sub.2 eliminated by the patient in a single breath (VCO.sub.2). [0109] 5. The method of any one of items 1 through 4, wherein the repeating measurement of the at least one patient-specific physiological parameter is effected by means of oxygraphy, preferably volumetric oxygraphy, by the ventilator, and wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters which comprise alveolar O.sub.2 partial pressure (PCO.sub.2) and/or volume of oxygen taken up by the patient in one breath (VO.sub.2). [0110] 6. The method of any one of items 1 through 5, wherein the at least one patient-specific physiological parameter corresponds to at least the parameter arterial CO.sub.2 partial pressure (PaCO.sub.2), the arterial CO.sub.2 partial pressure (PaCO.sub.2) being approximated via non-invasively measured patient-specific physiological parameters. [0111] 7. The method of any one of items 1 through 6, wherein the repeating measurement of the at least one patient-specific physiological parameter is effected by means of pulse oximetry, and wherein the at least one patient-specific physiological parameter corresponds to at least the parameter arterial oxygen saturation of the blood of the patient (SpO.sub.2). [0112] 8. The method of any one of items 1 through 7, wherein, as the at least one patient-specific physiological parameter, the parameter volumetric blood flow of the intrapulmonary right-to-left shunt of the patient (PBF.sub.SHUNT) is determined from the parameters which comprise alveolar oxygen concentration, amount of oxygen taken up by the patient in one breath and/or arterial oxygen saturation of the blood of the patient (SpO.sub.2). [0113] 9. The method of any one of items 1 through 8, wherein a recruiting maneuver is carried out at the start of an artificial ventilation, wherein lung overdistension is achieved by initial provision of an increased ventilation pressure, and then the ventilation pressure is reduced and a PEEP titration is carried out. [0114] 10. The method of any one of items 1 through 9, wherein the ventilation pressure amplitude is permanently monitored during artificial ventilation, an alarm being triggered if a preset maximum ventilation pressure amplitude is exceeded. [0115] 11. The method of any one of items 1 through 10, wherein based on a recording of at least one patient-specific physiological parameter, proportions (in %) and/or absolute values (in ml) for regions of the lungs/the lung filling are determined which, relative to at least the one patient-specific physiological parameter, represent anatomic dead space and/or represent alveolar dead space volume and/or represent functional alveoli and/or represent a shunt and/or represent VtCO2, the regions of the lungs being shown differently in a graph (by coloring or hatching) according to their proportions or absolute values and are preferably displayed in a graphic representation of the lungs. [0116] 12. A ventilator for artificial ventilation of a patient, preferably configured to be operated by a method according to any one of items 1 through 11, for operating a ventilator, which ventilator comprises: [0117] a measuring device, which is configured to record at least one patient-specific physiological parameter, [0118] a control device, which is configured to set at least one technical respiration parameter, wherein the ventilation of the patient takes place on the basis of the technical respiration parameter, at least one technical respiration parameter corresponding to at least one of the respiration parameters which comprise respiratory minute volume (VE), tidal volume (V.sub.T), respiratory rate (RR), positive end-expiratory pressure (PEEP), or the inspiratory oxygen concentration (FiO.sub.2) made available by the ventilator, and [0119] a regulator unit, which is in communication with the measuring device and with the control device, [0120] wherein the measuring device is configured in such a way that it carries out a repeating measurement of the at least one patient-specific physiological parameter at time intervals, and [0121] wherein the regulator unit is configured in such a way that it carries out an adaptation of the at least one technical respiration parameter on the basis of the repeating measurement of the patient-specific physiological parameter. [0122] 13. The ventilator of item 12, wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters which comprise airway dead space (V.sub.Daw), alveolar dead space (V.sub.Dalv) or physiological dead space (V.sub.Dphys) of the patient. [0123] 14. The ventilator of any one of items 12 or 13, wherein the measuring device furthermore is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter after each breath taken by the patient. [0124] 15. The ventilator of any one of items 12 through 14, wherein the measuring device is designed as a capnograph and is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter by capnography, preferably volumetric capnography, and wherein the at least one patient-specific physiological parameter corresponds to at least one parameter directly representing the CO.sub.2 gas exchange in the lungs of the patient, preferably at least one of the parameters comprising end-expiratory CO.sub.2 partial pressure in an exhaled gas mixture (PETCO.sub.2), alveolar CO.sub.2 partial pressure (PACO.sub.2), or volume of CO.sub.2 eliminated in a single breath by the patient (VCO.sub.2). [0125] 16. The ventilator of any one of items 12 through 15, wherein the measuring device is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter by means of oxygraphy, preferably volumetric oxygraphy, and wherein the at least one patient-specific physiological parameter corresponds to at least one of the parameters which comprise alveolar O.sub.2 partial pressure (PCO.sub.2) and/or volume of oxygen taken up by the patient in one breath (VO.sub.2). [0126] 17. The ventilator of any one of items 12 through 16, wherein the at least one patient-specific physiological parameter corresponds to at least the parameter arterial CO.sub.2 partial pressure (PaCO.sub.2), the measuring device being configured in such a way that it approximates the arterial CO.sub.2 partial pressure (PaCO.sub.2) via non-invasively measured patient-specific physiological parameters. [0127] 18. The ventilator of any one of items 12 through 17, wherein the measuring device is designed as a pulse oximeter and is configured in such a way that it carries out the repeating measurement of the at least one patient-specific physiological parameter by means of pulse oximetry, and wherein the at least one patient-specific physiological parameter corresponds at least to the parameter arterial oxygen saturation of the blood of the patient (SpO.sub.2). [0128] 19. The ventilator of any one of items 12 through 18, wherein the measuring device is configured in such a way that, as the at least one patient-specific physiological parameter, it determines the parameter volumetric blood flow of the intrapulmonary right-to-left shunt of the patient (PBF.sub.SHUNT) from the parameters comprising alveolar oxygen concentration, amount of oxygen taken up by the patient in one breath and/or arterial oxygen saturation of the blood of the patient (SpO.sub.2). [0129] 20. The ventilator of any one of items 12 through 19, wherein the control device is configured in such a way that it carries out a recruiting maneuver at the start of the artificial ventilation, wherein lung overdistension is achieved by initial provision of an increased ventilation pressure, and then the ventilation pressure is reduced and a PEEP titration is carried out. [0130] 21. The ventilator of any one of items 12 through 20, wherein a monitoring unit is provided, which is configured in such a way that a ventilation pressure amplitude is permanently monitored during an artificial ventilation, an alarm being triggered if a preset maximum ventilation pressure amplitude is exceeded. [0131] 22. The ventilator of any one of items 12 through 21, wherein based on a recording of at least one patient-specific physiological parameter, the control unit determines proportions (in %) and/or absolute values (in ml) for regions of the lungs/the lung filling which, relative to at least the one patient-specific physiological parameter, represent anatomic dead space and/or represent alveolar dead space volume and/or represent functional alveoli and/or represent a shunt and/or represent VtCO2, the regions of the lungs being shown differently in a graph (by coloring or hatching) according to their proportions or absolute values and preferably being displayed in a graphic representation of the lungs.