FR2908975A1 - METHOD FOR ACQUIRING THE REASPIRE EXPIRY GAS VOLUME IN A POWER-ASSISTED BREATHING SYSTEM - Google Patents

Abstract

The present invention relates to a method of acquiring the volume of re-aspirated exhalation gas which is re-aspirated by a user of a breathing system assisted with inspiratory pressure (pI) and expiratory pressure (pE) after expiration. Such an assisted respiration system comprises a breathing mask (10), an apparatus (12) for supplying breathing gas and a hose (5), which connects the apparatus (12) for supplying gas with breathing with the breathing mask (10). The process steps to be performed include determining the leak flow (FL) and a patient flow (Fpat) with subsequent comparison and evaluation of the difference. In addition, the concentration of carbon dioxide (cCO2, resp) is determined on a subsequent inspiration and compared with a limit value for the carbon dioxide concentration. For a carbon dioxide concentration (c CO2, resp) higher than the limit value, the breathing pressure is increased or an alarm is generated.

Description

Process for acquiring the volume of exhaled breath gas in a

  assisted breathing system. The invention relates to a method for acquiring the volume of exhaled expiration gas in an assisted respiration system. Open leakage systems for VINs require minimum pressures to ensure CO2 scrubbing for all possible combinations of respiration rate quantities, I: E ratio, leakage, pressure, volume and volumetric flow. This minimal pressure is naturally oriented on the worst case combination of the deep parameters. A standard value for such minimum pressure nowadays is for the usual combinations of devices (device + patient interface) in non-invasive breathing at 4 hPa. Assisted breathing devices for example, apnea patients, are known in the state of the art. During the duration of the assisted respiration, the patient wears a breathing mask, which is connected by a pipe or a pipe system, to a device supplying and delivering the breathing gas, so that a gas breathed by For example, air enriched with oxygen can be transmitted in the airways of the patient. During the inhalation phase, the patient takes the oxygen-enriched gas and, during the exhalation phase, discharges the oxygen-depleted air. The latter, depending on the shape of the mask, reaches at least partially in the mask space or into the pipe and is thus available, during the next phase of inspiration, to again feed the airways. So that the expelled air, which has an increased content of carbon dioxide, CO2r is not again sucked and directly deploys its toxic action, the respirators have devices (leakage element), which are used for the air rich in 002 is evacuated as directly as possible from the mask in the environment, so that it is not recycled in the mask space or in the pipe system. An assisted breathing mask, which has such a device for the evacuation of used air, is described in the document DE 101 58 066 A1. The assisted breathing mask described therein is used with a device for supplying air. oxygen and has a mask base body, which is connected by a coupling member to an exhalation element (leakage element), which limits a slot-like evacuation channel. Another mask is described in DE 199 03 732, which discloses a mask base body, which is connected by an exhalation element (leakage element) to a coupling element, which is connected by a breathing pipe assisted by an assisted breathing apparatus.

  Special uses, such as pediatric assisted breathing, require exhalation pressures of less than 4 hPa (eg, 2 hPa). For favorable ratios of breathing frequency, I: E ratio, leakage, pressure, volume and volumetric flow, CO2 washing is nevertheless possible with the leakage system. With the assisted breathing devices known in the state of the art, the assisted respiration processes are carried out, which are essentially based on the control and adjustment of the volume of breathing gas supplied to the patient. Are not captured, the volumes of gas exhaled by the patient, which to the extent that they remain in the dead volume of the assisted breathing device, especially in the mask, can be re-aspirated by the patient and thus represent a risk for health. From this state of the art, the present invention is based on the objective of providing an improved method of acquiring a volume of exhausted expired gas. This object is solved by a method with the features of claim 1. Preferred embodiments are described in the dependent claims. According to the invention, it is estimated in a first step, expiratory leak relative to the expired tidal volume of the patient. If the tidal volume is less than the exhalation leak, the exhaled CO2 enriched volume is completely washed out during exhalation. If this is not the case, a certain amount of CO2 is sucked up again. The intrapulmonary CO 2 concentration can then be estimated in a second step, considering the inspiratory leak and a worstcase study of the respiratory dead volume. This concentration is then compared to the general limit values for the CO2 load of the breathing air and, if necessary, an alarm is generated or the level of the assisted respiration pressure is recorded (EPAP or preferably, IPAP and EPAP for maintaining the effective pressure of assisted respiration - * increased wash).

In addition, it is conceivable that the calculation is refined by considering the volume of the dead space (dead volume of the mask, anatomical dead volume). For the usual masks, the appropriate data can be stored for example in a memory and extracted for calculation 10 (input of the system used on the assisted breathing apparatus). The volume of a patient's anatomical dead space can also be considered to increase accuracy. The dead volume can be estimated for example on the basis of body weight (e.g., the volume of the dead space in ml is about twice the body weight in kg). The exemplary embodiments of the present invention describe a method of acquiring the volume of expiration gas, re-aspirated. An exemplary embodiment is based on the acquisition of the volume of exhaled gas, which has expired in the assisted respiration system and which, based on the pressure ratios present in the system, as well as on the basis of gas flows and volumes, that may admit the gas, connected to the evacuation of gas out of the system by a present leak, is again sucked. The process according to the invention allows the acquisition of the corresponding gas flows and leakage volumes, wherein the volume of gas actually exhaled is confronted with the volume of evacuable exhalation gas and the volume of leakage over a given period. Since it turns out that the volume of exhalation gas to be evacuated does not correspond to the volume actually evacuated, a modification of the parameters of the system is caused, so that the ratios of gas exhaled gas escaping from the The system is modified in the sense that the patient is advantageously protected from the point of view of health, in that it is prevented from re-aspirating the 002-rich and toxic exhalation gas. Other exemplary embodiments of the present invention rely on the generation of an automatic alarm or signal when the flow of the system is changing to the disadvantage of the patient. An improved acquisition of the true CO2 concentration in the case of rebreathing (A> B) can be achieved in that the dead volume is determined using a refined study; in addition to the dead volume in the connection pipe and the mask, it is also possible to consider the dead volume in an exhalation chamber, if present, as well as the anatomical dead volume. The determination of the anatomical dead volume can be made for example on the basis of the previous determination of other anatomical factors, such as body weight. The relationship between body weight and anatomical dead volume can be determined as a factor and introduced into the calculating and operating unit, so that when changing the patient's weight, the mathematical consideration of the new anatomical dead volume is simply caused by the assisted breathing device, in which the new body weight multiplied by the factor simply gives the new dead volume to be considered. There are different ways to calculate the dead space. 2908975 6 - dead spaces (anatomic dead space and dead spaces of the interfaces used), which lead to a pendulum movement of the additional air, 5 - the specific anatomic dead space (on the basis of 1 kg of body weight) can be given approximately, by the following formula: Vesp. death anat. [ml / kg] = 3.28 - 0.56 x [ln (l + age *)] 10 * = age in years According to: Numa AH, Newth CJ. Division of Pediatric Critical Care, Los Angeles Children's Hospital, 15 University of Southern California 90027, USA. PMID: 8727530 [PubMed - indexed for MEDLINE]. - the doctor enters the age and body weight of the patient into the device, whereby the patient calculates the theoretical anatomical dead space.

The dead space (theoretical) of the mask can be considered, in that the user enters the type of mask in the device (where the stored parameters are retrieved) or in that the user (the physician) estimates the dead space based on the size of the mask, where appropriate taking into account an GA. The two dead spaces are used to determine the alveolar ventilation of the VT (tidal volume) determined. If a tubing is used in the breathing cycle, this is also mentioned.

In one embodiment of the invention, the amount of gas re-aspirated is determined in a system for supplying the breathing gas using certain parameters of respiration or respiration (pressure, frequency, etc.). During a breathing cycle, the exhalation flow and the leak flow are determined. By integrating these two streams on the exhalation phase, the resulting expiration and leakage volumes, as well as the amount of rebreathing (VR), are determined as the difference between the volume of exhalation and leakage volume (VR = VE VL). In another embodiment of the invention, volumes are determined on the apparatus upon acquisition of the absolute flux (Qabs = Qpmon + Qfuite). When these absolute flows exceed the zero value, the formed volume (VA) is calculated as a measure of the exhalation air stored temporarily in the system. The volume (VB) formed when the next absolute value of the absolute flow is exceeded until the beginning of the next inspiration is a measure of the system's washed volume. From these two volumes, the differential volume VR = VA - VB can be formed.

If VR> 0, the amount of CO2 is estimated in the following inspiration, which is formed at the end of the inspiration, by mixing the re-aspirated air with the fresh air in relation to the total inspired volume in the lungs (FiCO2).

In a preferred embodiment of the invention, when a critical value of the determined FiCO 2 is exceeded or for VR> 0, an alarm is generated, which warns the user or the recipient of the apparatus of a critical state.

In another preferred embodiment of the invention, when exceeding a critical value for the determined FiCO2 or VR> 0, the therapeutic pressure is increased at least temporarily during a breathing phase to increase the volume. leakage and to reduce the re-aspirated gas. To estimate the Fi002 in the alveoli, the anatomical dead space and the system can be considered so that the dead space of the system (eg, mask, hose) and / or anatomic dead space is filled at the beginning of the system. inspiration by its volume at the end of the previous expiration with air enriched in 002. Moreover, the empty space of the system and / or the anatomical void space can be considered at the end of the inspiration, as rich in 02 and poor in CO2r but can not be considered during the determination of FiCO2, for example in the cells, because this gas does not participate in the gas exchange alveolar.

The device proposed in the above method for supplying breathing gas has at least one source (pressure or flow) for supplying a breathing gas and at least one sensor for capturing the breathing flows. and other optional sensors for measuring pressure and other breathing parameters and means for adjusting and controlling the parameters of assisted respiration. The flow as well as the pressure can be measured at the exit of the apparatus, in the apparatus or directly on the patient interface. Other exemplary embodiments, as well as some advantages, which are related thereto and other exemplary embodiments, will be better understood by the following explicit description, supported by the figures. The figures are simple schematic representations of the embodiments of the invention. They show: FIG. 1, a diagrammatic representation of a respiration-assisted breathing apparatus, FIG. 2a, a graph for the representation of the development of the total flow and the leak flow during an inspiration phase FIG. 3a, a graph for the representation of the development of the total flow during an inspiration-expiration phase; FIG. 3b, a graph for the representation of the development of the pressure during an inspiration-expiration phase, Figure 4 is a graph for the representation of certain components of the invention.

Figure 1 shows a basic structure of an assisted respiration device. The apparatus for the supply of breathing gas comprises an appliance housing 1 with control panel 2 and a display 3 and has a breathing gas pump disposed in its interior space. By a coupling 4, a connecting pipe 5 is connected. On this connecting pipe 5, an additional pressure measuring pipe 6 may extend, which may be connected by a pressure inlet piece 7 to the housing of the apparatus 1. To enable data transfer, the The housing of the apparatus 1 has an interface 8. At an extension of the connecting pipe 5, opposite the housing of the apparatus 1, there is arranged an expiratory element 9. An exhalation valve with an element 30 leakage (not shown) may also be used. The breathing mask shown in FIG. 1 is formed as a nasal mask 10. It is attached to the head of a patient by a helmet 11. At the level of its extension towards the connecting pipe 5, the nasal mask 10 has a coupling element 12. The connecting pipe thus connects the nasal mask and the housing of the apparatus 1, whereby the flow of breathing gas enters the mask. By way of example, Figure 2a shows the development of an isolated flow during an inspiration-expiration cycle. The total flux FG is shown, which first increases sharply in the inspiratory phase, reaches a plateau and falls sharply during the expiration phase, where the zero line is exceeded. During the expiration phase, the flow increases where it reaches the positive domain. The leakage flow FL, I develops during the inspiration phase, constantly at a level whose height depends on the adjusted pressure pI. Because the pressure pE present during the expiration phase is lower, the leakage flow FL, E during the expiration phase develops at a lower level, but also constant. If the leakage flux is subtracted at each moment from the total flow, the inspiratory and expiratory flow FI, FE is obtained. The development of the curve represented in FIG. 3a of the total flow FG shows, as a function of the actual current volume, a variation of the total flux FG shown in FIG. 2a by the leakage flux FL, which develops in a manner similar to the flow shown in Figure 2a. Figure 3b shows the established pressure pI, pE. Figures 3a and 3b clearly show that rebreathing in the assisted breathing system, also in the mask or pipe, occurs only for a total flow FG that is less than zero. This occurs precisely when the leakage volume is too small in relation to the total flow, to evacuate the exhalation flow FE; see Figure 3a. When the flow measured on the apparatus side is less than zero, which is the case at the first intersection of the total flux curve with the zero line, the surface A, as shown in FIG. a new positive passage (second intersection point) of the zero line. From this second point of intersection of the total flux curve with the zero line to the point of intersection of the total flux line with the leak flow line calculated according to (1), the surface B is seized. When the surface A is larger than the surface B, the gas exhaled by the patient is not completely exhausted by the leak. There is a re-aspiration, ie the patient is breathing some of his own expired gas enriched in 002. This is disadvantageous when the exhaled air of the patient contains a higher concentration of CO2 than an ambient air envisioned in current scales as without risk to health. In addition to the CPAP and BIPAP applications indicated above, the method according to the invention can also be used with medical devices such as APAP, Bilevel, titration, home-assisted breathing, assisted respiration and emergency or assisted breathing in the clinic. Figure 4 shows a graph to facilitate understanding of the device as well as the method. In addition to the expiratory volume evaluation unit, there is also an expiratory leak volume evaluation unit in the apparatus. The values of these evaluation units are entered into the calculation unit for the determination of the concentration in 002. If the rebreathing quantity is greater than 0 or the FiCO2 is greater than a determined limit value, an alarm can expressed or an adaptation of the pressure can be achieved. First to warn the user of an alarm situation, then to decrease the extent of enrichment in 002 by changing the system parameters. Abbreviations CO2 Carbon dioxide 0002 Concentration of carbon dioxide cCO2r resp. Concentration 002 of PE breathing Expiratory pressure, PI device side Inspiratory pressure, VT device side Tidal volume Vmort Dead volume VG = VL + VT Total gas volume VG, E = VT, E + VT, E Total gas volume, which s flow during expiration FGI = FLI + Fpatl Inflammatory flow FGE = FLE + FpatE Expiratory flow FL Leakage flow FG = FL + Fpat Total flow, applies to inspiration and expiration FT, I inspiratory patient flow FT, E Expiratory patient flow FL, E Expiratory leak flow FL, I Inspiratory leakage flow 2908975 13 FG, E Total exhalation flow Fpat Patient flow VE Exhalation volume (VT) VL Leakage volume VR Re-aspiration quantity Qabs Absolute flow (measured / determined on the device) Qpoumon Absolute leakage flux Qfuite Absolute flow of the patient

Claims (20)

  A method for determining the amount of gas re-aspirated in a breathing gas supply system using determined parameters of respiration or assisted respiration (pressure, frequency, etc.), in that during a breathing cycle, captures the exhalation flow and the leakage flow, characterized in that the expiration and leakage volumes resulting each time from the integration of these two flows are determined and the amount of rebreathing (VR) is determined as the difference between the exhalation volume and the leakage volume (VR = VE - VL).   2. Method according to claim 1, characterized in that the determination of the volume is achieved by the acquisition of the absolute flow (Qabs = Qpmon + Qfuite), where when exceeding the zero value of this absolute flow, the volume formed (VA) is a measure of the exhalation air temporarily stored in the system and in that the volume (VB) formed when the next value is exceeded from the absolute flow to the beginning of the next inspiration is as a measure of the washed volume of the system and the differential volume VR = VA - VB is formed.   3. Method according to claim 1 or 2, characterized in that when VR> 0, the amount of CO2 in the following inspiration, which is formed by mixing the re-aspirated air with the fresh air in relation to the volume inspired sucked into the lung, at the end of inspiration (FiCO2), is estimated.   4. Method according to one of claims 1 to 3, characterized in that when exceeding a critical value for the Fi002 determined or VR> 0, an alarm is generated.   5. Method according to one of claims 1 to 4, characterized in that when exceeding a critical value for the determined FiCO2 or VR> 0, the therapy pressure is increased to increase the volume of leakage and for reduce the gas re-aspirated at least temporarily during a breathing phase.   6. Method according to one of claims 2 to 5, characterized in that the estimate of F1002 is performed by considering the anatomical dead volume.   7. A method according to claim 6, characterized in that the anatomical dead volume is determined and / or estimated using approximation and patient information functions (age and / or weight and / or sex and / or or size).   8. Method according to one of the preceding claims, characterized in that the estimate is made further by considering the dead volume of the system (eg, mask, pipe).   9. Method according to one of the preceding claims, characterized in that the dead volume of the system and / or the anatomical dead volume at the beginning of the inspiration is considered so that its volume is filled with air rich in CO2 to the end of the previous expiration.   10. Method according to one of the preceding claims, characterized in that the dead volume of the system and / or the anatomical dead volume is considered at the end of inspiration, as rich in 02 and low in CO2r but in determining the Fi002, it is not considered that this gas does not participate in the exchange of alveolar gas. 2908975 16   11. Device for supplying breathing gas, which has at least one source (pressure or flow) for supplying a breathing gas and at least one sensor for capturing the flow of respiration and respiration. other optional sensors for measuring the pressure by means for adjusting and controlling the parameters of the assisted respiration and wherein during a breathing cycle, the exhalation flow and the leak flow are captured, characterized in that the volumes of Expiration and leakage are determined by integration of these two flows and the amount of rebreathing (VR) is determined as the difference of the exhalation volume and the leakage volume (VR = VE - VL). 15   12. Device according to claim 11, characterized in that the determination of the volume is achieved by the acquisition of the absolute flow (Qabs = Qpmon + Qfuite) with the aid of a flow sensor device side, where for exceeding the zero value of this absolute flow, the formed volume (VA) is formed as the measure of the accumulated exhalation air previously in the system and the volume (VB) formed when the next value is exceeded From the absolute flow to the beginning of the next inspiration is formed as the measure of the washed volume of the system and the differential volume VR = VA - VB is formed.   13. Device according to claim 11 or 12, characterized in that for VR> 0, the amount of 002 is estimated in the following inspiration which is formed at the end of the inspiration, by the mixture of the re-aspirated air with fresh air in relation to the total inspired volume in the lungs (Fi002). 2908975 17   14. Device according to one of claims 11 to 13, characterized in that when exceeding a critical value FiCO2 determined or VR> 0, an alarm is generated. 5   15. Device according to one of claims 11 to 14, characterized in that when exceeding a critical value for the determined FiCO2 or VR> 0, the therapeutic pressure is increased at least temporarily during a breathing phase for 10 to increase the volume of leakage and to reduce the re-aspirated gas.   16. Device according to one of claims 12 to 15, characterized in that the estimate FiCO2 is made by considering the anatomical dead space. 15   Device according to claim 16, characterized in that the anatomical void space is determined and / or estimated by means of approximation functions and patient information (age and / or weight and / or sex and / or or size). 20   18. Device according to one of the preceding claims, characterized in that the estimate is made further, considering the empty space of the system (eg, mask, pipe).   19. Device according to one of the preceding claims, characterized in that the empty space of the system can be considered at the end of the inspiration, so that its volume is filled at the end of the previous expiration, air rich in CO2.   20. Device according to one of the preceding claims, characterized in that the empty space of the system can be considered at the end of the inspiration, as rich in 02 and low in CO2, but can not be considered when the determination of FiCO2, because this gas does not participate in alveolar gas exchange.