Method and ventilation device for determining respiratory gas content in the respiratory tract during artificial ventilation

Description

[0001] The present invention relates to a method for determining a respiratory tract content of respiratory gas present in the respiratory tract of an at least partially artificially ventilated patient after several breaths performed with the involvement of a ventilator, wherein the multiple breaths comprise at least one previous breath volume and at least one subsequent breath volume following the previous breath volume. The previous breath volume comprises a previous breath volume or a plurality of consecutive previous breaths. The method comprises quantitatively detecting inspiratory and expiratory respiratory gas flows by at least one respiratory gas flow sensor and summing detected inspiratory and expiratory flow values ​​to determine the respiratory gas respiratory tract content.

[0002] The invention also relates to a ventilation device for at least partially artificially respirating a patient, which is designed to carry out the method described here.

[0003] Such a method and a ventilation device using this method are known from WO 2019 / 094736 A1. WO 2019 / 094736 A1 teaches that a ventilation phenomenon of "double triggering," explained further below, can be inferred when the expiration duration is in a predetermined ratio to the inspiration duration or exceeds or falls below threshold values ​​based on such a predetermined ratio.

[0004] WO 2019 / 094736 A1 also teaches that a ventilation phenomenon similar to "double triggering" can be inferred when the expiratory volume is less than the inspiratory volume, particularly when the difference between the expiratory volume and the inspiratory volume exceeds a predetermined threshold. According to WO 2019 / 094736 A1, the consequence of detecting "air trapping" is the labeling of the relevant breath as an air-trapping breath.

[0005] In general, respiratory gas volumes on ventilators are determined by integrating the recorded respiratory gas flows over the period of interest—usually numerical integration due to the use of digital data processing. For example, on ventilators, the delivered inspiratory gas volume is determined by integrating the recorded inspiratory gas flows, i.e., the respiratory gas flows flowing to the patient, from the beginning of the inspiration process to its end. Likewise, the expiratory gas volume delivered by the patient can be determined by integrating the recorded expiratory gas flows over the duration of the expiration process, i.e., from the beginning of the expiration process to its end.

[0006] Knowledge of, for example, inspiratory gas volumes can be important for controlling a ventilator to determine whether a patient has been administered the tidal volume determined by the attending staff (this is the amount of gas to be delivered per breath in volume-based ventilation control). If this is the case, a ventilator operating in a volume-based ventilation mode, for example, switches from inspiration to expiration.

[0007] Respiratory gas flows are often continuously recorded and integrated to determine the amount of respiratory gas present or remaining in the patient's respiratory tract at any given time. Inspiratory and expiratory respiratory gas flows are distinguished by different mathematical signs due to their opposite directions—one toward the patient and one away from the patient. When integrating the respiratory gas flows, the inspiratory respiratory gas volume in the patient is initially accumulated during an inspiration process and then reduced again during a subsequent expiration process.

[0008] Ideally, the same amount of respiratory gas flows away from the patient during the expiration phase as previously flowed to the patient during the inspiration phase. However, flow sensors in ventilators can detect respiratory gas flows in opposite directions with varying accuracy, either due to a calibration deficiency or due to manufacturing inaccuracies, which can manifest themselves in directionally asymmetric detection accuracy. A calibration deficiency can arise, for example, if a flow sensor is exposed to moisture from the respiratory gas, which condenses in the area of ​​the flow sensor. Due to increasing or changing moisture exposure, the flow sensor deviates increasingly or to a changing extent from its calibration.The moisture can condense to different degrees upstream and downstream of the flow sensor, especially a differential pressure flow sensor, and thus cause asymmetric detection behavior with regard to the flow direction of the respiratory gas.

[0009] The result is a drift in the sensor signal representing the respiratory volume, observable over several breaths. Due to this drift, the sensor signal deviates increasingly in magnitude from a theoretically error-free sensor signal over time.

[0010] To avoid such drift, some state-of-the-art ventilation devices are designed to separately determine the patient's respiratory tract content of respiratory gas (respiratory gas respiratory tract content) for each breath, independent of the result of the respiratory tract content measurement for the immediately preceding breath. With continuous measurement of the respiratory gas respiratory tract content, this corresponds to resetting the measured respiratory tract content to zero at the end of a previous breath, so that the respiratory tract content measurement for the subsequent breath starts from zero.

[0011] While this can prevent the described drift, there is a risk that such a regular resetting of the summary recording of inspiratory and expiratory gas volumes may mask other events relevant for the evaluation of a ventilation process, such as so-called "breath stacking," triggered, for example, by "double triggering" or a short expiration. In this event, no or only an incomplete expiration occurs between two triggered inspirations, so that in the subsequent breath after the incomplete expiration, the tidal volume specified by the ventilator is again administered to the significant residual amount of respiratory gas remaining in the patient's respiratory tract as respiratory tract contents.Since the respiratory tract contents remaining in the patient's respiratory tract at the end of the incomplete expiration of the previous breath are not detected due to the reset to zero when the respiratory gas volumes are recorded, the administration of the tidal volume in the subsequent breath creates an undesirably high respiratory gas pressure and an undesirably high respiratory gas volume in the patient's respiratory tract, which is at least unpleasant for the patient but represents an undesirable medical risk.

[0012] US Patent No. 8757152 B1 discloses various methods for inferring the occurrence of double triggering of an inspiration event based on ventilation parameters of a current ventilation session. However, these methods have no influence on the determination of the respiratory gas content in a subsequent breath following a previous breath.

[0013] It is therefore an object of the present invention to further develop the method mentioned at the outset for determining a respiratory gas respiratory tract content and a ventilation device designed to carry out the method in such a way that a drift of a sensor signal representing the respiratory gas respiratory tract content of a patient can be sufficiently reliably avoided without thereby masking out a medically relevant respiratory stacking.

[0014] The present invention achieves this objective with the method mentioned at the outset in that a respiratory tract content initial value, with which the determination of the respiratory gas respiratory tract content for the subsequent breath begins, is set, depending on a respiratory gas quantity difference between an inspiratory respiratory gas quantity supplied to the patient during the previous breath quantity and an expiratory respiratory gas quantity delivered by the patient during the previous breath quantity, to a reset initial value that is closer to zero than a difference value quantitatively indicating the respiratory gas quantity difference, or to a continuity initial value that is closer to the difference value than zero. Thus, for example, if the respiratory gas quantity difference is small in magnitude, for example, smaller than a difference threshold value, the reset initial value can be set as the respiratory tract content initial value.This should be the norm for artificial ventilation, so the described drift can be prevented by using the reset initial value. Furthermore, if the respiratory gas volume difference is large, for example, greater than the difference threshold, the continuity initial value can be set as the respiratory tract content initial value. This makes it possible to detect unusual ventilation events, which are reflected in the respiratory gas volumes taken in and delivered by the patient, while still avoiding unwanted signal drift.

[0015] This allows small deviations in the inspiratory and expiratory gas volumes to be leveled out or masked out, while deviations that are sufficiently large to be taken into account are transferred as the initial value for determining the respiratory gas content for the subsequent breath. Consequently, when determining the respiratory gas content for the subsequent breath, the fact that the patient's respiratory tract is already partially filled with respiratory gas at the beginning of the subsequent breath is taken into account.

[0016] The term "respiratory tract" refers to a patient's upper and lower respiratory tract. The body organ commonly referred to as the "lungs" is part of the lower respiratory tract.

[0017] Preferably, the summation of the inspiratory and expiratory gas flows across the majority of breaths is a balanced summation, which takes into account opposing gas flows with different mathematical signs. For example, all gas flows supplied to the patient can be positive, while all gas flows flowing away from the patient can be negative.The continuous summation of respiratory gas flows with different signs results in the summation of similarly directed respiratory gas flows of one and the same respiratory stroke segment, such as an inspiration sequence, resulting in an inspiratory gas volume that increases in magnitude. This respiratory gas volume is then reduced again in magnitude in a subsequent expiration sequence, a further respiratory stroke segment, with respiratory gas flows that are equal to one another within the expiration sequence but opposite to the previous inspiration sequence, by the continuously summed respiratory gas flows with opposite signs. At any time during a respiratory stroke, the respiratory gas volume determined in this way provides a sufficiently accurate indication of the patient's current respiratory gas content in the respiratory tract.If the determination of the respiratory gas content begins at the beginning of the first breath assisted by the ventilator with an initial respiratory gas content, the respiratory gas content determined over the majority of previously completed respiratory gas strokes indicates the change compared to the initial respiratory gas content. Since determining the respiratory gas content present in a patient's respiratory tract outside of artificial ventilation involves considerable effort, the initial respiratory gas content is generally zero. The respiratory gas content determined using the method proposed here is therefore preferably a respiratory gas content in addition to the generally unknown initial respiratory gas content.The respiratory gas respiratory tract content indicates that part of the total amount of respiratory gas moved by the ventilator during a ventilation treatment that currently remains in the patient's respiratory tract.

[0018] The difference value quantitatively indicates the difference in the amount of respiratory gas between the total inspiratory respiratory gas quantity supplied in the previous breath and the total expiratory respiratory gas quantity flowed out of the patient in the same previous breath, which, neglecting any leakage losses in the valves and in the respiratory gas-carrying lines of the ventilator and, if applicable, also in the area of ​​the respiratory tract itself, corresponds to the respiratory gas respiratory tract content present in the patient's respiratory tract at the end of the previous breath.

[0019] For clarification, a breath according to the present application comprises at least one inspiration event and, as a rule, also one expiration event. As described above, the expiration event may be incomplete due to breath stacking or double triggering, whereby the incompleteness of an expiration event also includes the complete failure of an expiration event.

[0020] In principle, it is possible to consider selecting the reset initial value within a predetermined value range that is closer to zero than the difference value. The same applies, mutatis mutandis, to the continuity initial value, which can be selected within a predetermined value range that is closer to the difference value than zero. To completely and reliably avoid drift, the reset initial value is preferably zero. Additionally or alternatively, the continuity initial value is preferably the difference value to ensure that the determination of the respiratory tract content initial value for the subsequent breath begins with the respiratory tract content breathing gas volume at the end of the previous breath volume immediately preceding the subsequent breath volume as the initial value.An integration of respiratory gas flows continued beyond a respiratory stroke limit, so that the determination of the respiratory tract content initial value for the subsequent respiratory stroke begins with the respiratory tract content respiratory gas quantity at the end of the previous respiratory stroke quantity immediately preceding the subsequent respiratory stroke as the initial value, is a setting of the respiratory tract content initial value to the difference value within the meaning of the present application.

[0021] Preferably, the initial respiratory tract content value is determined repeatedly during a uniform, continuous ventilation treatment on a patient in order to eliminate drift error during as long a period of artificial ventilation as possible, but without also eliminating respiratory stacking.

[0022] In principle, it is also possible to correct any drift only after a predetermined number of breaths, so that the previous breath volume can comprise a plurality of immediately consecutive previous breaths. The previous breath volume is followed by a subsequent breath, for which the initial value of the respiratory tract content is to be determined. However, if the previous breath volume contains too many breaths, a drift error accumulated over these many breaths may be difficult to distinguish from breath stacking in an otherwise drift-free recording of the respiratory gas respiratory tract content, resulting in an undesirably high error rate.

[0023] To ensure that a drift error for determining the respiratory tract content initial value of the subsequent breath can be sufficiently clearly distinguished from the effect of breath stacking, according to a preferred development of the present invention, for a plurality of consecutive breaths, the earlier breath volume contains exactly one earlier breath. This enables the further advantageous development that, for each earlier breath from a plurality of earlier breaths, an initial respiratory tract content value is determined for the respective subsequent breath depending on the respiratory gas volume difference. In this case, breaths that are subsequent breaths in a determination of an initial respiratory tract content value are each an earlier breath in a subsequent determination of the initial respiratory tract content value.

[0024] In a simple yet robust embodiment of the method, the difference value itself can be used as a criterion to decide whether the reset initial value or the continuity initial value is set as the respiratory tract content initial value. Greater freedom in determining the respiratory tract content initial value, and thus, greater accuracy in determining the respiratory gas respiratory tract content, can be achieved by additionally determining a decision value in the method, where the decision value represents the respiratory gas volume difference.

[0025] It may be sufficient for the decision value to represent the difference in respiratory gas volume qualitatively or indirectly. For example, the decision value can assess the difference in respiratory gas volume based on a difference between the time duration of the at least one inspiration process and the time duration of the at least one expiration process of the previous respiratory stroke volume, and can infer a difference in the associated inspiratory and expiratory respiratory gas volumes from the difference between the said time durations. The decision value can be a predetermined function of the time duration of the at least one inspiration process and the time duration of the at least one expiration process of the previous respiratory stroke volume. The decision value can, for example, be proportional to a quotient of the time duration of the at least one inspiration process and the time duration of the at least one expiration process of the previous respiratory stroke volume.

[0026] A particularly accurate decision for one or the other respiratory tract content initial value can be made if the decision value represents the difference value. The decision value can be a predetermined function of the difference value. Advantageous embodiments of the decision value are discussed further below. When determining the respiratory tract content initial value, the reset initial value or the continuity initial value can then be determined as the respiratory tract content initial value, depending on the decision value.

[0027] Then, if, as described above, it applies to a plurality of consecutive breaths that the previous breath quantity contains exactly one previous breath, a decision value can consequently be determined for each of a plurality of previous breaths and, depending on the respective decision value, a respiratory tract content initial value can be determined for each subsequent breath following an earlier breath from the plurality of previous breaths.

[0028] The use of a decision value that differs in magnitude from the difference value but represents the difference value makes it possible, for example, to relate the difference value to the total volume of respiratory gas moved during the previous breath volume, which is advantageous for the meaningfulness of the decision value. This is because a given absolute parameter of a ventilation treatment, such as partial breath duration in seconds or a difference value in volume, mass, or weight, must be medically assessed differently depending on whether it occurred in a ventilated infant or a ventilated adult.

[0029] Preferably, the decision value relates the difference value to the inspiratory gas volume delivered to the patient during the previous breath volume. The decision value can therefore be proportional to a quotient of the difference value and the inspiratory gas volume delivered to the patient with the involvement of the ventilator during the previous breath volume. The proportionality factor can be selected according to the characteristics of the ventilator used, for example, taking into account a leakage loss occurring with each breath. However, it is sufficient to select the value 1 for the proportionality factor so that the decision value is equal to the above-mentioned quotient. Its inverse, which has the same information content and thus the same significance, is also considered a quotient.As already indicated above, the decision value can be the difference value itself, although this is not preferred for the reasons stated above.

[0030] Determining the initial respiratory tract content value based on the decision value can advantageously include a comparison of the decision value with a predetermined decision threshold, with the initial respiratory tract content value being determined based on the result of the comparison. The decision threshold can be selected based on a series of tests on the ventilation device used so that the error rate of unwanted false-positively detected respiratory stacks that did not actually occur and / or unwanted false-negatively undetected actual respiratory stacks is as low as possible.

[0031] The preferred repeated determination of an initial respiratory tract content value during artificial ventilation can result in artifacts that, as time progresses, paint an increasingly unrealistic picture of the actual amount of respiratory gas moved during artificial ventilation.

[0032] For example, the applicant knows from medical observations that breath stacks cannot occur any number of times in succession, since the physically limited respiratory tract volume of a patient makes it impossible to administer the tidal volume set on the ventilator any number of times in succession to an incompletely exhaling patient. Therefore, the method proposed here can provide for the reset initial value to be set as the respiratory tract content initial value, regardless of the respiratory gas quantity difference, in particular regardless of the decision value, if the continuity initial value was previously set as the respiratory tract content initial value each time during a predetermined first number of consecutive determinations of the respiratory tract content initial value.Previous research has shown that 4 is a suitable predetermined first number, although the first number could also be 3 or 5 or even 6.

[0033] Under the same aspect of physiologically impossible excessive administration of the tidal volume without sufficient expiration in between, the reset initial value can then be set as the respiratory tract content initial value regardless of the respiratory gas volume difference, in particular regardless of the decision value, if previously, within a predetermined second number of determinations of the respiratory tract content initial value, the number of determinations that resulted in the continuity initial value reaches or exceeds a predetermined proportion threshold, wherein the proportion threshold is smaller than the second number. Likewise, the second number is preferably larger than the first number. The proportion threshold can be a percentage threshold or an absolute threshold. For example, the proportion threshold can be 50%, or the proportion threshold can be 5 determinations for a second number of 10 determinations.In the case of a percentage-defined threshold, the second number of determinations can be changed as a reference value in a data processing program that carries out the proposed method with less effort than in the case of an absolutely defined threshold.

[0034] Likewise, alternatively or preferably additionally, it can be provided that the reset initial value is determined as the respiratory tract content initial value independently of the respiratory gas quantity difference, in particular independently of the decision value, if, within a predetermined number of previously executed breaths, a frequency with which a quotient of a first respiratory tract content difference and a second respiratory tract content difference different from the first reaches or exceeds a predetermined quotient threshold value, reaches or exceeds a frequency threshold value. The first respiratory tract content difference is preferably a difference between the respiratory gas respiratory tract content at the end of a specific respiratory stroke and the respiratory tract content of respiratory gas at the end of an earlier respiratory stroke quantity preceding the specific respiratory stroke.The second respiratory tract content difference is preferably a difference between the respiratory tract content of respiratory gas at the end of an inspiration phase of the specific breath and the respiratory tract content of respiratory gas at the end of the previous breath volume preceding the specific breath. In formulaic terms, this means for a preferred embodiment: . V endexp , i − V endexp , i − 1 V endinsp , i − V endexp , i − 1 ≥ QS

[0035] The increment or count index i refers to the later breath being considered, i.e., in the above terminology, the specific breath within the predetermined number of previously performed breaths. The specific breath can be freely selected, but should not be the first breath of the ventilation process, as it must be preceded by a breath. Preferably, the specific breath is the breath immediately preceding the subsequent breath.

[0036] The increment or count index i-1 thus refers to the previous breath quantity immediately preceding the specific breath, in particular to the immediately preceding previous breath. In equation 1, V endexp,i the respiratory gas content of the respiratory tract at the end of a specific breath, i.e. at the end of the expiratory phase of the specific breath; V endexp,i -1 denotes the respiratory gas content of the respiratory tract at the end of the previous respiratory stroke preceding the specific respiratory stroke, in particular of a previous respiratory stroke, i.e. again at the end of an expiratory phase; V endinsp,i QS refers to the respiratory gas content of the respiratory tract at the end of an inspiration phase of the subsequent breath, and QS is the quotient threshold. The quotient threshold can be determined based on experimental studies. It is preferably between 0.1 and 0.3, preferably between 0.15 and 0.25, and most preferably 0.2.

[0037] The frequency threshold can be approximately 40% to 80% as a percentage threshold. Preferably, the frequency threshold is in a range between 40% and 60%, particularly preferably 50%.

[0038] The predetermined frequency may be between 5 and 20 breaths, preferably between 8 and 15 breaths, particularly preferably 10 breaths.

[0039] Another possible misassessment of the respiratory gas content can be due to a change in positive end-expiratory pressure (PEEP) during artificial ventilation. Due to the known relationships between pressure and volume of gases, a change in PEEP also means a change in the end-expiratory respiratory gas content. To advantageously avoid an misassessment of the respiratory gas content caused by a change in PEEP, the proposed method can provide for the reset initial value to be determined as the respiratory tract content initial value regardless of the respiratory gas volume difference, in particular regardless of the decision value, if a quantitative change in PEEP was detected within a predetermined period of time prior to the current determination of the respiratory tract content initial value.The predetermined time period can be defined relative to a reference time period. The predetermined time period and / or the reference time period can be defined absolutely as a time period in seconds, minutes, and the like. However, the predetermined time period and / or the reference time period can also be defined functionally, for example, by the duration of a predetermined number of previous breaths or breath sections. A breath section can be, for example, the inspiration phase or the expiration phase of the breath.

[0040] Furthermore, during artificial ventilation, especially after a breath stack, but also at other times, exceptionally deep exhalations occasionally occur, during which the patient exhales more expiratory gas than they took in during the previous inspiration phase. After such a deep exhalation with an above-average expiratory gas volume, the patient's respiratory tract is most likely not partially filled with respiratory gas to a medically critical extent.Therefore, the reset initial value can be determined as the respiratory tract content initial value independently of the respiratory gas volume difference, in particular independently of the decision value, if it is determined for at least one of the two previous respiratory stroke volumes immediately preceding the current subsequent respiratory stroke for which the respiratory tract content initial value is determined, in particular for at least one of the two immediately preceding previous respiratory strokes, that an expiratory respiratory gas volume of the previous respiratory stroke volume determined from the recorded expiratory respiratory gas flows is greater in magnitude than an inspiratory respiratory gas volume of the same previous respiratory stroke volume determined from the inspiratory respiratory gas flows. In a preferred embodiment, this means, firstly, that immediately after an aforementioned deep expiration, the determination of the respiratory tract content can begin with the reset initial value, since in this case there is no risk of breath stacking.In a preferred embodiment, this also means that the determination of the respiratory tract content can begin immediately after an incomplete expiration with the reset initial value, even if a deep expiration occurred immediately before the incomplete expiration. In this latter case, breath stacking does occur, but in a previously over-exhaled respiratory tract, so that even after the incomplete expiration, there is no risk of excessive strain on the respiratory tract due to breath stacking.

[0041] To facilitate monitoring of the ventilation process, the respiratory tract content of respiratory gas can be displayed graphically as a function of time on an output device.

[0042] The above-mentioned objective technical problem is also solved by a ventilation device for at least partially artificially respirating a patient, comprising: a respiratory gas source arrangement which provides an inspiratory respiratory gas for artificial ventilation of the patient, a flow change device which is designed to generate an inspiratory respiratory gas flow and to change its amount, a respiratory gas line arrangement with a proximal longitudinal end which is closer to the patient during operation and with a distal longitudinal end which is further away from the patient during operation in order to promote the inspiratory respiratory gas flow from the respiratory gas source arrangement to the patient, a flow sensor arrangement which is designed to record the inspiratory respiratory gas flow as well as the expiratory respiratory gas flow in terms of amount, a control device with a data memory, wherein the control device is connected to the data memory and to the flow sensor arrangement for signal transmission and which is designed toto control the operating performance of the flow change device to change the inspiratory respiratory gas flow, The control device is configured to execute the above-described and advantageously further developed method. The control device can comprise a processor with integrated circuits and a data memory with a program stored thereon that can be retrieved and executed by the processor, wherein the execution of the program by the processor leads to the execution of the above-described method.

[0043] The breathing gas source arrangement of the ventilator can have an intake opening as a breathing gas source, through which ambient air or gas from a predetermined gas supply can be drawn in. The breathing gas source arrangement can additionally or alternatively have a gas supply as a breathing gas source, for example as a reservoir or as a connection formation for connecting a supply line that connects the ventilator to a locally installed gas supply, as is often the case in hospitals. To provide the option of mixing different gases into a breathing gas, the breathing gas source arrangement can have a plurality of individual breathing gas sources, such as those mentioned above. The different gases to be mixed can have different temperatures and / or different humidities due to their individual supply and expansion.In order to ensure that the inspiratory breathing gas actually reaches the patient with a humidity once set, it is particularly preferred that no further breathing gas component is added to the breathing gas flow exiting from the humidification device downstream of a preferably present humidification device in the inspiration direction.

[0044] The flow sensor arrangement can have one or more flow sensors, for example one each for the inspiratory and expiratory respiratory gas flow. Preferably, the flow sensor arrangement comprises only one flow sensor to detect both the inspiratory and expiratory respiratory gas flow. This is preferably arranged proximally between the respiratory gas line arrangement and a patient interface, but can also be accommodated distally in a housing of the ventilator, in which, for example, the flow modification device is also accommodated. To achieve greater process reliability, the ventilator can also have multiple flow sensors, each of which detects both the inspiratory and expiratory respiratory gas flow, for example a distal flow sensor in a housing of the ventilator and a proximal flow sensor close to the patient.

[0045] Preferably, the ventilation device comprises a pressure sensor arrangement, which may also comprise one or more pressure sensors to measure the pressure of the inspiratory and / or expiratory respiratory gas.

[0046] The flow sensor arrangement preferably comprises a differential pressure flow sensor, so that the differential pressure flow sensor at the location where the respiratory gas flow is detected also enables the detection of the prevailing respiratory gas pressure. Particularly preferably, the flow sensor arrangement is a proximal, patient-proximal flow sensor arrangement. For example, the proximal flow sensor arrangement, with which the respiratory gas flows are detected to determine the initial values ​​of the respiratory tract contents, is located no further than 80 cm, preferably no further than 50 cm, from the patient's mouth. A proximal flow sensor arrangement exhibits better synchronization than a distal flow sensor arrangement located further away from the patient and thus allows more precise detection of a patient-induced triggering of an inspiration process, i.e., an inspiration effort by the patient.

[0047] Preferably, the ventilation device, in particular the control device, also comprises a time measuring device in order to be able to determine the durations of processes and sub-processes during a ventilation treatment.

[0048] To realize the graphical output of the determined respiratory gas content as a function of time, the ventilation device preferably has a graphical output device, such as a monitor or a touchscreen. The control device is then preferably configured to graphically output the determined respiratory gas content as a function of time on the output device.

[0049] In order to give a therapist accompanying a patient's artificial ventilation the easy possibility to quickly and reliably detect a potentially critical respiratory stack, the graphical output of the respiratory tract content of respiratory gas as a function of time on the output device can include the measure of changing the graphical output of the respiratory tract content as a function of time when the continuity initial value is set as the respiratory tract content initial value.

[0050] The change in the graphical output can be a change in the graph of the respiratory tract content as a function of time, such as a change in the line color and / or the line thickness, such as between thin and thick line thickness, and / or the line type, such as between dotted and / or dashed and / or solid line.

[0051] Additionally or alternatively, the change in the graphical output can be a change in at least a portion of the background on which the graph of respiratory tract content is displayed as a function of time. For example, the color and / or texture of the background, such as between hatched and solid, can be changed. This can involve changing either the entire background or just a portion between the graph and a reference line, such as the zero line of respiratory tract content.

[0052] In principle, a change in the graphical output can be a change in the entire graphical output, including parts that represent the temporal progression of past respiratory tract contents. This applies in particular, but not exclusively, to a change in the background.

[0053] The accompanying therapist can be made more easily aware not only of the fact that breath stacking has occurred, but also of when it occurred, by making the change in the graphical output only effective from the moment the continuity initial value is selected as the respiratory tract content initial value, and by keeping previously displayed graphical content unchanged. The ventilation device is configured accordingly to implement this modified graphical output.

[0054] For input and, more generally, output of data, the ventilation device preferably comprises an input / output device controllable by the control device, which may also include the aforementioned graphical output device. The input / output device may comprise a plurality of buttons, rotary switches, a touchscreen, a loudspeaker, lighting devices, and the like. Likewise, the ventilation device may have data interfaces and / or data transmission lines for receiving data from and / or transmitting data to other devices. Data interfaces may be sockets, radio antennas, plugs, and the like.

[0055] In principle, the ventilator is preferably designed to ventilate a patient according to different ventilation modes, from which the attending physician can select when setting up the ventilator. For example, the ventilator can artificially ventilate a patient using volume-based or pressure-based control. Since breath stacking or double triggering is particularly important when performing supportive orIf support ventilation modes occur in which a patient can trigger artificial inspiration supported by the ventilation device through an inspiratory effort, the ventilation device is preferably designed to perform artificial ventilation in a support ventilation mode in which the control device detects an inspiratory effort of the ventilated patient and, upon detecting the inspiratory effort, controls the flow change device to administer an inspiratory respiratory gas quantity to the patient via the respiratory gas line arrangement. An inspiratory effort can be detected, for example, by monitoring a respiratory gas flow and / or a respiratory gas pressure in the respiratory gas line arrangement for sudden, typical changes.

[0056] To mitigate the effects of undesired breath stacking or double triggering, the control device is preferably designed to detect incomplete expiration based on the respiratory tract content initial value determined according to the method and / or based on the determined respiratory tract content of respiratory gas. If the continuity initial value is set as the respiratory tract content initial value, incomplete expiration can be easily and reliably detected by exceeding one or more threshold values ​​for the respiratory gas respiratory tract content during a subsequent inspiration. Preferably, the control device is designed to change the ventilation mode when the control device has detected incomplete expiration, in particular to switch between a volume-controlled ventilation mode and a pressure-controlled ventilation mode.Of particular interest is the change from a volume-controlled ventilation mode, which threatens to "overfill" the incompletely exhaled respiratory tract, to a pressure-controlled ventilation mode, which, for example, controls for a respiratory gas pressure value to be reached during inspiration and not for the delivery of a predetermined tidal volume.

[0057] The aforementioned respiratory gas quantity can be a mass, a weight, or a volume of respiratory gas. Preferably, the respiratory gas quantity is a respiratory gas volume, as is preferred and common in medical ventilation technology.

[0058] The present invention will be explained in more detail below with reference to the accompanying drawings. It shows: Figure 1 shows a schematic representation of a ventilation device according to the invention, designed for the artificial ventilation of a patient, and Figure 2 shows a graphic output of a time course of the respiratory gas respiratory tract content of an artificially ventilated patient, once created using a conventional determination method and once using the method proposed here, and Figure 3 shows a flow diagram of a sequence of an embodiment of the method proposed here according to the invention.

[0059] In Figure 1 An embodiment of a ventilation device according to the invention is generally designated 10. In the example shown, the ventilation device 10 serves for the artificial ventilation of a preferably human patient 12.

[0060] The ventilation device 10 has a housing 14 in which an intake opening 15 is formed and—not visible from the outside due to the opaque housing material—a flow-changing device 16 and a control device 18 are accommodated. The intake opening 15 allows the flow-changing device 16 to draw in ambient air from the external environment U of the ventilation device and, after conventional purification by filters, to supply it as breathing gas to the patient 12. The intake opening 15 is therefore a breathing gas source arrangement within the meaning of the present application.

[0061] An ambient temperature sensor 17 can be located in the intake opening 15, which measures the temperature of the ambient air U and transmits it to the control device 18.

[0062] The flow-changing device 16 is constructed in a manner known per se and may include a pump, a compressor, a blower, a pressure vessel, a pressure reducing valve, and the like. Furthermore, the ventilation device 10 includes, in a manner known per se, an inspiration valve 20 and an expiration valve 22.

[0063] The control device 18 is usually implemented as a computer or microprocessor. It comprises a Figure 1The data memory, designated 19, is used to store data necessary for the operation of the ventilator 10 and to retrieve it if necessary. In network operation, the data memory 19 can also be located outside the housing 14 and connected to the control device 18 via a data transmission link. The data transmission link can be formed by a cable or a radio link. However, to prevent disruptions in the data transmission link from affecting the operation of the ventilator 10, the data memory 19 is preferably integrated into the control device 18 or at least accommodated in the same housing 14 as the control device.

[0064] For inputting data into the ventilator 10 or more precisely into the control device 18, the ventilator 10 may have an input device 24, which is arranged in the Figure 1In the example shown, this is represented by a keyboard. As will be explained further below, the keyboard is not necessarily the only data input of the control device 18. In fact, in addition to or alternatively to the keyboard, the control device 18 can receive data via various data inputs, for example via a network line, a radio link, or via sensor connections 26.

[0065] To output data to the treating therapist, the ventilator 10 may have an output device 28, in the example shown a monitor.

[0066] For artificial ventilation, the patient 12 is connected to the ventilation device 10, more precisely to the flow-modifying device 16 in the housing 14, via a respiratory gas line assembly 30. For this purpose, the patient 12 is intubated using an endotracheal tube as a patient interface 31. A proximal longitudinal end 31a of the patient interface 31 delivers the inspiratory respiratory gas flow AF into the respiratory tract 12a of the patient 12. The expiratory respiratory gas flow EF also flows into the respiratory gas line assembly 30 through the proximal longitudinal end 31a.

[0067] The respiratory tract 12a of patient 12 comprises the upper respiratory tract 12a1 and the lower respiratory tract 12a2. The body organ commonly referred to as the "lung" belongs to the lower respiratory tract 12a2.

[0068] A distal longitudinal end 31b of the patient interface 31 is configured for connection to the breathing gas line assembly 30. From the location 31c downstream in the inspiration direction to the proximal longitudinal end 31a, the patient interface is surrounded by the body of the patient 12. Conversely, this means that the patient interface 31 is exposed to the external environment U from its distal longitudinal end 31b to the location 31c and is in predominantly convective heat transfer connection with it.

[0069] The respiratory gas line arrangement 30 has an inspiration tube 32, via which fresh respiratory gas can be supplied from the flow-modifying device 16 into the respiratory tract 12a of the patient 12. The inspiration tube 32 can be interrupted and comprise a first inspiration tube 34 and a second inspiration tube 36, between which a humidification device 38 can be provided for the targeted humidification and, if necessary, also temperature control of the inspiratory respiratory gas supplied to the patient 12. The humidification device 38 can be connected to an external liquid supply 40, via which water for humidification or a medication, for example for anti-inflammatory purposes or for dilating the airways, can be supplied to the humidification device 38.When the present ventilator 10 is used as an anesthesia ventilator, volatile anesthetics can be delivered to the patient 12 in a controlled manner via the ventilator 10. The humidification device 38 ensures that the fresh respiratory gas is supplied to the patient 12 at a predetermined humidity, optionally with the addition of a medication aerosol, and at a predetermined temperature.

[0070] In the present example, the second inspiratory tube 36 is electrically heated by a line heating device 37. The line heating device 37 can be activated for operation by the control device 18. Deviating from the above, the first inspiratory tube 34 can also be heated and / or the at least one tube 34 and / or 36 can be heated by a device other than an electrical line heating device 37, for example, by flushing with a heat exchange medium.

[0071] In addition to the already mentioned inspiration valve 20 and expiration valve 22, the breathing gas line arrangement 30 further comprises an expiration tube 42, via which metabolized breathing gas is blown off as expiratory breathing gas flow EF from the respiratory tract 12a of the patient 12 into the outside environment U.

[0072] At the distal longitudinal end 30b of the breathing gas line assembly 30, the inspiratory tube 32 is coupled to the inspiratory valve 20, and the expiratory tube 42 is coupled to the expiratory valve 22. Preferably, only one of the two valves is open at a time to allow the passage of a gas flow. The actuation of the valves 20 and 22 is also controlled by the control device 18.

[0073] During a ventilation cycle, the expiration valve 22 is initially closed and the inspiration valve 20 is opened for the duration of the inspiration phase, allowing fresh inspiratory gas to be directed from the housing 14 to the patient 12. A flow of fresh gas is achieved by a targeted increase in the pressure of the gas through the flow-modifying device 16. Due to the pressure increase, the fresh gas flows into the respiratory tract 12a of the patient 12 and expands the body area near the respiratory tract, particularly the rib cage, against the individual elasticity of the body parts near the respiratory tract. This also increases the gas pressure inside the respiratory tract 12a of the patient 12.

[0074] At the end of the inspiration phase, the inspiration valve 20 is closed and the expiration valve 22 is opened. The expiration phase begins. Due to the increased gas pressure of the respiratory gas present in the respiratory tract 12a of the patient 12 until the end of the inspiration phase, this gas flows into the outside environment U after the expiration valve 22 opens, with the gas pressure in the respiratory tract 12a of the patient 12 decreasing as the flow duration progresses. If the gas pressure in the respiratory tract 12a reaches a positive end-expiratory pressure (PEEP) set on the ventilator 10, i.e., a pressure slightly higher than atmospheric pressure, the expiration phase is ended with the closing of the expiration valve 22, and another ventilation cycle follows.

[0075] During the inspiration phase, patient 12 is supplied with the ventilation tidal volume set for patient 12, i.e., the respiratory gas volume per breath, in a volume-based assisted ventilation mode, for example. The ventilation tidal volume multiplied by the number of ventilation cycles per minute, i.e., multiplied by the ventilation rate, results in the minute volume of the artificial ventilation being performed.

[0076] Preferably, the ventilation device 10, in particular the control device 18, is designed to repeatedly update or determine ventilation operating parameters that characterize the ventilation operation of the ventilation device 10 during ventilation operation, in order to ensure that the ventilation operation is optimally tailored to the respective patient 12 to be ventilated at all times. Particularly advantageously, one or more ventilation operating parameters are determined using the ventilation frequency, so that current ventilation operating parameters that are thus optimally adapted to the patient 12 can be provided for each ventilation cycle.

[0077] For this purpose, the ventilator 10 can be connected to one or more sensors for data transmission, which monitor the condition of the patient and / or the operation of the ventilator 10. As such a sensor, the ventilator 10 has a proximal differential pressure flow sensor 44, which measures the respiratory gas flow prevailing in the respiratory gas line arrangement 30, namely both the inspiratory respiratory gas flow AF and the expiratory respiratory gas flow EF ,The proximal differential pressure flow sensor 44 is coupled to the data inputs 26 of the control device 18 by means of a sensor line arrangement 46. The sensor line arrangement 46 may, but need not, include electrical signal transmission lines. It may also have hose lines that transmit the gas pressure prevailing in the flow direction on both sides of a flow resistance of the differential pressure flow sensor 44 to the data inputs 26, where this pressure is quantified by pressure sensors 27.

[0078] More specifically, in the preferred embodiment, the breathing gas line arrangement 30 has a separately formed Y-line section 47 at its proximal longitudinal end region 30a, which is connected at its distal end region to the second inspiration tube 36 and the expiration tube 42 and which is connected at its proximal end region to the proximal flow sensor 44.

[0079] The proximal flow sensor 44 has a coupling formation 44a at its proximal end region, with which the patient interface 31, which could also be a mask instead of a tube, can be coupled to the proximal flow sensor 44 and consequently to the breathing gas line arrangement 30.

[0080] The second inspiration tube 36 may have a proximal temperature sensor 48 at its proximal longitudinal end region, which measures the temperature of the respiratory gas flow AF in the second inspiration tube 36 as close as possible to the patient 12 and transmits it to the control device 18.

[0081] For the sake of completeness, it should be noted that the ventilation device 10 according to the invention can be accommodated as a mobile ventilation device 10 on a rollable frame 50.

[0082] In Figure 2A graphical output of the respiratory gas volume balance of patient 12 over several breaths is shown as an example. The abscissa of the coordinate system of Figure 2 indicates the time in seconds, the ordinate the amount of respiratory gas currently remaining in the patient 12, i.e. the respiratory gas respiratory tract content, as respiratory gas volume in milliliters.

[0083] A graph 52 shows the result of a conventional method for determining the amount of respiratory gas currently remaining in the patient 12 as the respiratory gas respiratory tract content as a respiratory gas volume balance. During the conventional determination of the respiratory gas respiratory tract content of the patient 12, the initial quantity value of the respiratory gas volume balance is reset to zero by the control device 18 before each breath to prevent a drift in the signal 52. Such a drift could be caused by faulty calibration and / or by manufacturing tolerances of the differential pressure flow sensor 44. The manufacturing tolerances can have the effect that the differential pressure flow sensor 44 outputs or generates flow signals that differ slightly in magnitude during inspiration and expiration for the same respiratory gas flow.

[0084] The control device 18 integrates the flows detected by the differential pressure flow sensor 44 over the duration of a breath to determine the respiratory gas content of the respiratory tract. In the illustration of Figure 2 Each local upper peak of graph 52 is assigned to a different breath, with the rising edge being generated by the inspiration process of a breath and the falling edge by the expiration process of the same breath. Since the respiratory gas volume balance or the respiratory gas respiratory tract content begins at zero at the beginning of each breath in conventional determination, inspiratory respiratory gas flows are integrated with positive amounts and expiratory respiratory gas flows with negative amounts. The breaths are addressed below with consecutive numbers, starting with breath number 1 at 0 seconds. For easier orientation, some breaths are identified by their numbers in a circle.

[0085] Line 54 indicates a target respiratory gas volume or a target respiratory gas volume at the end of the inspiration phase of each breath. This target respiratory gas volume corresponds to the aforementioned ventilation tidal volume.

[0086] Line 56, parallel to line 54, indicates a first limit value for the respiratory gas content of the respiratory tract, which corresponds to 1.5 times the target value of the ventilatory tidal volume. Line 58 indicates a second limit value for the respiratory gas content of the respiratory tract, which corresponds to twice the target value of the ventilatory tidal volume.

[0087] The Figure 2 The respiratory gas volume balance shown is a theoretically generated respiratory gas volume balance to illustrate the procedure used here. It is not a respiratory gas volume balance determined on a real patient.

[0088] During breaths No. 2 and No. 4 of Figure 2Excessive expiration occurs, during which the patient 12 releases more respiratory gas than they previously received during the inspiration phase. This can occur, for example, due to a slight cough at the end of expiration or due to the spontaneous removal of a flow obstruction, such as a buildup of mucus in the airways. It can be clearly seen how the subsequent breath no. 3 is forcibly set to zero by the control device in relation to the earlier breath no. 2 at the start of the determination of the respiratory gas respiratory tract content during the subsequent breath no. 3; this can be seen by the vertical line segment 60 connecting the end of expiration of breath no. 2 with the start of inspiration of breath no. 3. The same applies to the subsequent breath no. 5 in relation to its immediately preceding earlier breath no. 4.

[0089] The excessive expiration shown, in which the graphically displayed respiratory gas volume balance becomes negative, can occur, for example, if the integration of the respiratory gas flows occurring during each breath begins at zero for each breath and is not integrated beyond the end of a breath. However, it should not be forgotten that although breath number 1 begins with a respiratory gas volume of zero, a positive respiratory gas volume other than zero was present in the respiratory tract 12a of patient 12 at this time as the initial respiratory gas respiratory tract content.

[0090] In the example shown, the ventilator 10 operates in a volume-related controlled support ventilation mode, according to which the set ventilation tidal volume is administered to the patient 12 either when the PEEP is detected in the breathing gas line, which indicates the end of an inspiration, or when the patient 12 shows spontaneous breathing, i.e. makes an inspiration effort or triggers an inspiration.

[0091] As in Fig. 2As can be clearly seen, the expiration process in breath no. 6 is incomplete and ends by triggering an inspiration process at approximately 15 seconds (dotted line 62). Due to the convention of the conventional method for determining the respiratory gas content of patient 12, which avoids signal drift, the initial value of the respiratory gas content or the respiratory gas volume balance for the subsequent breath no. 7, based on the previous breath no. 6, is set to zero, from which the inspiration process of breath no. 7 is recorded using graph 52.

[0092] Due to the permanent resetting of the patient's 12 respiratory gas content at the beginning of a breath, breath number 7 also appears in graph 52 as if the patient 12 were only properly receiving the ventilation tidal volume. As a consequence of the respiratory tract 12a actually being overfilled with respiratory gas during breath number 7, a drastic apparent over-emptying of the patient's respiratory tract 12a occurs in graph 52 when the conventional procedure is applied at the end of breath number 7.

[0093] In fact, the over-emptying shown at the end of breath No. 7 in graph 52 does not occur. Passive expiration, which is usually only driven by the positive pressure generated during inspiration in the patient's respiratory tract 12a relative to the ambient atmosphere as the sink for expiratory respiratory gas, merely causes the excess respiratory gas content of the respiratory tract, which is due to the previous incomplete expiration in breath No. 6, to be released after the end of the inspiration process of breath No. 7.

[0094] The graph 64 in Figure 2 shows the respiratory gas content of the respiratory tract determined according to the method described here. This runs in the control device 18 according to the Figure 3 flowchart shown.

[0095] The control device 18 samples the respiratory gas flow values ​​detected by the differential pressure flow sensor 44 at a frequency f. Consequently, the control device 18 receives a new respiratory gas flow value every time a time Δt = 1 / f has elapsed.

[0096] At step S10 in Figure 3 the control device 18 queries the differential pressure flow sensor 44 and receives a respiratory gas flow value F in response.

[0097] In the subsequent step S20, the control device 18 checks whether the respiratory gas flow value F was recorded at the beginning of a new breath, i.e. at the beginning of a new inspiration phase, because only at the beginning of a new breath is it necessary to check whether the previously determined respiratory gas respiratory tract content of a previous breath should be updated by setting an initial value for the determination of the respiratory gas respiratory tract content for the newly beginning subsequent breath or whether the determination of the respiratory gas respiratory tract content should start at zero.

[0098] Then, when the obtained respiratory gas flow value F was detected at the beginning of a subsequent breath, the method proceeds to step S30, in which a decision value is determined and compared with a decision threshold value.

[0099] The decision value is, for example, the difference value of the previous breath related to the inspiratory respiratory gas quantity of the previous breath, which quantifies a balance difference between the inspiratory and expiratory respiratory gas quantity of the previous breath.

[0100] Since the previous breath No. 6 started with an initial value of 0 ml, at point 66 in Figure 2, at which expiration in the previous breath no. 6 ends prematurely and the subsequent breath no. 7 begins, the value of the respiratory gas quantity balance according to graph 52 (and also according to graph 64, which at this point still coincides with graph 52), the difference between the respiratory gas quantity inspired in the previous breath no. 7 and the respiratory gas quantity exhaled in the same breath no. 7. The difference is approximately 220 ml. The inspiratory respiratory gas quantity of the previous breath no. 6 is the local peak value of graph 52, at which the gradient of graph 52 reverses. It is approximately 340 ml.

[0101] The decision value is therefore 220 ml / 340 ml = 0.65. Based on previous experiments and studies, a value of 0.25 was chosen as the decision threshold. The decision value exceeds the decision threshold, so the method proceeds to step S40.

[0102] In step S40, a check is performed to determine whether an incremental counting variable, which counts the frequency of consecutive exceedances of the decision threshold by the decision value, is less than or equal to a predetermined limit value, which specifies a maximum permissible number of consecutive exceedances of the decision threshold. In this case, the predetermined limit value is 3.

[0103] Since in the previous breaths Nos. 1 to 6 the decision threshold has not been exceeded due to the essentially complete expiration, but this happens for the first time at the beginning of the subsequent breath No. 7, the method proceeds to step S50.

[0104] In step S50, it is checked whether the above-mentioned equation 1 was not fulfilled more often than 50% for the last 10 breaths, whereby 0.2 is chosen for the quotient threshold based on experiments and medical examinations.

[0105] Since there are no preceding 10 breaths until the beginning of the subsequent breath No. 7, step S50 is executed for the existing number of preceding 6 breaths.

[0106] The use of equation 1 is explained below using the example of breath no. 4 with i=4: the end-expiratory respiratory gas volume of breath no. 4, see point 68, is approximately -30 ml. The end-expiratory respiratory gas volume of the previous breath no. i-1=3, see point 70, is approximately 0 ml. The end-inspiratory respiratory gas volume of breath no. 4 is just below the target ventilation tidal volume of approximately 350 ml. Using equation 1, these values ​​give the left-hand side of equation 1 the value -0.08, which, due to the negative sign alone, is certainly not greater than the quotient threshold of 0.2. The result is similar for the remaining breaths nos. 1 to 6; the quotient threshold was not exceeded. Consequently, equation 1 was in the values ​​corresponding to the following breath no.7 preceding breaths are met for less than half of the breaths, whereby the frequency threshold, which is, for example, a value of 50%, has not been reached. The method then proceeds to step S60.

[0107] In step S60, a check is made to determine whether an excessively large expiration occurred in the previous breath no. 5 relative to the immediately preceding breath no. 6. A large expiration, in which more respiratory gas is expelled by the patient 12 than was previously inspired, results in a negative end-expiratory breathing gas volume. The criterion for determining whether an excessively large expiration has occurred is whether the end-expiratory breathing gas volume of the immediately preceding previous breath no. 6 is greater than the negative end-expiratory breathing gas volume of the previous breath no. 5 (see equation 2). V endexp , i > − V endexp , i − 1

[0108] The end-expiratory gas volume of breath no. 5 is negative, but only slightly at approximately -25 ml. The end-expiratory gas volume of breath no. 6, at approximately 220 ml, is greater than the end-expiratory gas volume of breath no. 5 multiplied by -1. Therefore, the method proceeds to step S70.

[0109] In step S70, a check is made to determine whether PEEP was increased within a predetermined period of time prior to the subsequent breath number 7, for example, during the last two breath numbers 5 and 6. This is not the case. Consequently, the method proceeds to step S80.

[0110] When step S80 is reached, it is clear that all criteria for detecting incomplete expiration and thus breath stacking are met. In step S80, the ventilation mode is changed from the previously performed volume-based assisted ventilation to pressure-based assisted ventilation. Furthermore, the pressure support value for the changed ventilation mode is preferably set to a pressure value that is set to the average end-inspiratory respiratory gas pressure of a predetermined number of immediately preceding breaths, for example, the last 10 breaths, minus the PEEP. This is intended to prevent the tidal volume from being administered again after a detected incomplete expiration. The method then proceeds to step S90.

[0111] Step S80, which involves changing the ventilation mode, is only one possible variant of the method. Often, treating therapists do not want the ventilation device to change the ventilation mode independently. The method can also continue directly from step S70 to step S90.

[0112] In the graphically in Figure 2 During the ventilation process shown, no change in ventilation mode took place.

[0113] In step S90, the count variable indicating the frequency of consecutive incomplete expirations is incremented by 1. The method then proceeds to step S100.

[0114] In step S100, the end-expiratory respiratory gas volume of the immediately preceding previous breath No. 6 is set as the continuity initial value for determining the respiratory gas respiratory tract content during the subsequent breath No. 7. The method proceeds to step S110.

[0115] In step S110, the respiratory gas volume flowing so far is determined by numerical integration from the respiratory gas flow obtained in step S10. It is assumed that the detected respiratory gas flow F continues to flow until the next respiratory gas flow is detected, i.e., for the duration Δt. The respiratory gas respiratory tract volume AL determined in step S110 for the kth detected respiratory gas flow from a total of n respiratory gas flows of the subsequent breath under consideration thus corresponds to the following equation 3: AL k = V Anfangswert + ∑ k = 1 n F k ⋅ Δ t where V initial value is the initial value for determining the respiratory gas content in the subsequent breath. As described above, after passing through the method branch containing step S100, the initial value is the continuity initial value, ie, the end-expiratory respiratory gas volume in the patient's respiratory tract in the previous breath immediately preceding the subsequent breath.

[0116] After performing the numerical integration in step S110, the method returns to step S10 where the next respiratory gas flow is detected.

[0117] Since the method only serves to determine an initial value for determining a respiratory gas respiratory tract content of the patient 12, the method then proceeds at step S20, if the detected respiratory gas flow is not at the beginning of a breath, directly to the numerical integration of step S110.

[0118] Steps S40 to S70 do not have to be executed, but they increase the accuracy of the method. The method can also lead to the process branches with steps S100 or S140 exclusively in step S30 based on the formation of the decision value and its comparison with a decision threshold.

[0119] Then, if in one of the steps S30 to S70 one of the criteria mentioned is not assessed as described above, the method flow does not reach steps S80 or S90, but enters the alternative branch, where step S120 is processed next.

[0120] Step S120, which is not mandatory, confirms the continuation of the previously selected volume-based, assisted ventilation mode.

[0121] In any case, if the criteria assessment differs in one of the steps S30 to S70, the alternative step S130 corresponding to the previously explained step S90 is reached, in which the counting variable for counting the frequency of immediately consecutive breath stacks, i.e. incomplete expiration, is reset to zero, since the immediately preceding earlier breath did not have a breath stack.

[0122] The method then continues to step S140, in which the initial value for determining the respiratory gas content for the subsequent breath is reset to the initial reset value of zero. This means that when the method branch is completed with step S140, V initial value is equal to zero.

[0123] The method then proceeds to step S110, already explained above, in which the numerical integration of the detected species flow F(k) takes place.

[0124] For better clarity, Figure 2 Graph 52, which conventionally shows the respiratory gas content of the patient 12 with the initial value reset to zero before each breath, and graph 64, which shows the determination of the respiratory gas content of the patient 12 according to the method presented here, are provided with multiple reference symbols. In principle, Figure 2The graph sections that significantly fall below the zero line belong to graph 52, and the peak values ​​that almost or completely reach line 56 belong to graph 64. Between a junction of graph 64 with graph 52 and a renewed separation of graph 64 from graph 52, the two graphs 64 and 52 run along a common line, which is explained by the common integration rule.

[0125] In order to make incomplete expiration and the subsequent re-administration of the tidal volume as easily, quickly, and reliably recognizable as possible to a therapist observing the graphic output of the respiratory gas respiratory tract content, the control device 18 is configured to change the graphic representation of the respiratory gas respiratory tract content as a function of time from the time at which the continuity initial value is set as the respiratory tract content initial value. This change in the representation can, for example, continue until an end-expiratory respiratory tract content is reached that falls below a predetermined graphic change threshold or differs in amount by no more than a predetermined graphic change amount from the average end-expiratory respiratory tract content of the last n breaths, where n can be, for example, 5 or 10 or another integer.

[0126] For breath number 7, the graphical output of the respiratory gas content is modified by changing the line type and color. For breath number 9, the graphical output of the respiratory gas content is modified by changing the line thickness from thinner to thicker.

[0127] At breath number 7, after the incomplete expiration of breath number 6, the results of the conventional determination of the respiratory gas content and the results of the determination according to the method discussed here differ for the first time. This is followed by breath number 8, again with incomplete expiration, a normal breath number 9, a breath number 10 with incomplete expiration, followed by even-numbered breaths up to breath number 30, which feature an incomplete expiration, followed by odd-numbered breaths with complete expiration. From breath number 32 onwards, including this breath number, no more breath stacks occur.

[0128] The following special features should be noted: at the end of expiration of breath 15, patient 12 exhales deeply, so that the end-expiratory respiratory gas volume in the respiratory tract of patient 12a becomes negative. Since the end-inspiratory respiratory gas volume of breath 15 is positive, as is any end-inspiratory respiratory gas volume, the decision value determined in step S30 is also negative and thus smaller than the decision threshold. As a result, the reset initial value is set as the respiratory tract content initial value for determining the respiratory gas respiratory tract content of the subsequent breath 16.

[0129] In breath no. 16, patient 12 triggers another inspiration phase immediately after the end of inspiration, so that patient 12 is administered a second tidal volume immediately following a first tidal volume. After the subsequent expiration in breath no. 17, the decision value formed in step S30 is smaller than the decision threshold due to the high end-inspiratory gas volume of breath no. 17, so the reset initial value is set as the respiratory tract content initial value for the subsequent breath no. 18.

[0130] The graphical representation of the ventilation process by displaying the respiratory gas content as a function of time in Figure 2 Graph 64 avoids unwanted drift and yet provides more intuitively understandable information about the inspiratory and expiratory gas volumes of the ventilation process.

Claims

1. Method for determining respiratory gas content in a respiratory tract, which is present in the respiratory tract (12a) of an at least partially artificially ventilated patient (12) after several breaths performed under the participation of a ventilation apparatus (10), where the several breaths exhibit at least one earlier breath set and at least one subsequent breath following the earlier breath set, where the earlier breath set exhibits one earlier breath or a plurality of successive earlier breaths, where the method comprises quantitative acquisition of inspiratory and expiratory respiratory gas flows (S10) through at least one respiratory gas flow sensor (44) and summation of acquired inspiratory and expiratory flow values to the respiratory tract content of respiratory gas (S110), characterized in that a respiratory tract content starting value, with which the determination of the respiratory gas content in a respiratory tract for the subsequent breath begins, depending on a respiratory gas quantity difference between an inspiratory respiratory gas quantity supplied to the patient (12) during the earlier breath set and an expiratory respiratory gas quantity exhaled by the patient (12) during the earlier breath set, is set to a reset starting value lying nearer to zero than to a difference value indicating quantitatively the respiratory gas quantity difference (S140) or to a continuity starting value lying nearer to the difference value than to zero (S100).

2. Method according to Claim 1, characterized in that the reset starting value is zero and / or that the continuity starting value is the difference value.

3. Method according to one of the Claims 1 or 2, characterized in that the respiratory tract content starting value is determined repeatedly during an at least partial artificial ventilation of a patient (12).

4. Method according to one of the preceding Claims, characterized in that the method comprises ascertaining a decision value (S30), where the decision value represents the respiratory gas quantity difference, in particular the difference value, where depending on the decision value the reset starting value or the continuity starting value is determined as the respiratory tract content starting value for the subsequent breath.

5. Method according to Claim 4, characterized in that the decision value is proportional to a ratio of the difference value and an inspiratory respiratory gas quantity supplied to the patient under the participation of the ventilation apparatus (10) during the earlier breath set (S30).

6. Method according to Claim 4 or 5, characterized in that the determination of the respiratory tract content starting values comprises, in dependence on the decision value, a comparison of the decision value with a predetermined decision threshold value, where the respiratory tract content starting value is determined in dependence of a result of the comparison (S30).

7. Method according to one of the preceding Claims, in consideration of Claim 3, characterized in that the reset starting value is determined independently from the respiratory gas quantity difference as the respiratory tract content starting value when previously in a predetermined first number of successive determinations of the respiratory tract content starting value each time the continuity starting value was determined as the respiratory tract content starting value (S40).

8. Method according to one of the preceding Claims, in consideration of Claim 3, characterized in that the reset starting value is determined independently from the respiratory gas quantity difference as the respiratory tract content starting value when previously within a predetermined second number of determinations of the respiratory tract content starting value the number of determinations which had as a result the continuity starting value reaches or exceeds a predetermined fraction threshold value, where the fraction threshold value is smaller than the second number.

9. Method according to one of the preceding Claims, in consideration of Claim 3, characterized in that the reset starting value is determined as the respiratory tract content starting value independently from the respiratory gas quantity difference when previously within a predetermined number of breaths it is the case that the frequency at which a ratio of a first respiratory tract content difference and a second respiratory tract content difference which differs from the first reaches or exceeds a predetermined ratio threshold value, reaches or exceeds a frequency threshold value, where preferably the first respiratory tract content difference is a difference between the respiratory gas content in a respiratory tract at the end of a particular breath and the respiratory gas content in a respiratory tract at the end of an earlier breath set preceding the particular breath and / or where the second respiratory tract content difference is a difference between a respiratory gas content in a respiratory tract at the end of an inspiration phase of the determined breath and the respiratory gas content in a respiratory tract at the end of the earlier breath set preceding the particular breath (S50).

10. Method according to one of the preceding Claims, characterized in that the reset starting value is determined as the respiratory tract content starting value independently from the respiratory gas quantity difference when for at least one of the two earlier breath sets directly preceding the current subsequent breath for which the respiratory tract content starting value is being determined, it is ascertained that an expiratory respiratory gas volume of the earlier breath set ascertained from the acquired expiratory respiratory gas flows is quantitatively greater than an inspiratory respiratory gas volume of the same earlier breath set ascertained from the inspiratory respiratory gas flows.

11. Method according to one of the preceding Claims, characterized in that the reset starting value is determined as the respiratory tract content starting value independently from the respiratory gas quantity difference when within a predetermined time interval before the current determination of the respiratory tract content starting value a quantitative change in the PEEP was acquired (S70).

12. Method according to one of the preceding Claims, characterized in that the respiratory gas content in a respiratory tract is output graphically as a function of time at an output device (28), wherein in particular, when the continuity starting value is set as the respiratory tract content starting value, the graphic output of the respiratory tract content is changed as a function of time.

13. Ventilation apparatus (10) for at least partial artificial ventilation of a patient (12), comprising: - a respiratory gas source arrangement (15) which provides an inspiratory respiratory gas for artificial ventilation of the patient (12), - a flow modification device (16) which is configured create and quantitatively to modify an inspiratory respiratory gas flow (AF), - a respiratory gas line arrangement (30) with a proximal longitudinal end which during operation lies nearer to the patient (12) and with a distal longitudinal end which during operation lies further away from the patient (12), in order to convey the inspiratory respiratory gas flow (AF) from the respiratory gas source arrangement (15) up to the patient (12), - a flow sensor arrangement (44) which is configured quantitatively to acquire the inspiratory respiratory gas flow (AF) and likewise an expiratory respiratory gas flow (EF), - a control device (18) with a data store (19), where the control device (18) is linked for signal transmission with the data store (19) and with the flow sensor arrangement (44) and which is configured to control the operational performance of the flow modification device (16) for modifying the inspiratory respiratory gas flow (AF), characterized in that the control device (16) is configured to implement the method according to one of the preceding Claims, wherein preferably the ventilation apparatus (10) exhibits a graphic output device (28), and the control device (28) is configured to implement the method according to Claim 12.

14. Ventilation apparatus (10) according to Claim 13, Characterized in that the ventilation apparatus (10) is configured to perform artificial ventilation in a support ventilation mode, in which the control device (16) acquires an inspiration effort of the ventilated patient (12) and on acquiring the inspiration effort actuates the flow modification device (16) to administer to the patient (12) an inspiratory respiratory gas quantity via the respiratory gas line arrangement (30), wherein preferably the control device (18) is configured to recognize an incomplete expiration on the basis of the determined respiratory tract content starting value and / or on the basis of the determined respiratory tract content of respiratory gas, and when the control device (18) has recognized an incomplete expiration, to change the ventilation mode, in particular to change between a volume-relatedly controlled ventilation mode and a pressure-relatedly controlled ventilation mode.

15. Ventilation apparatus (10) according to one of the Claims 13 to 14, Characterized in that the flow sensor arrangement (44) on the basis of whose acquisition values the respiratory tract content starting value is determined, is a proximal flow sensor arrangement (44).