VENTILATION APPARATUS FOR CARDIOPULMONARY RESUSCITATION WITH MONITORING AND DISPLAY OF THE MAXIMUM CO2 VALUE MEASURED

Abstract

The invention relates to a medical respiratory assistance apparatus for delivering a respiratory gas such as air, which may or may not be enriched with oxygen, to a patient during cardiopulmonary resuscitation (CPR), having a source (1) of respiratory gas, for example a micro-blower, for delivering a respiratory gas to said patient during cardiopulmonary resuscitation (CPR), and means (4) for measuring the CO.sub.2 content, signal-processing and control means (5), and at least one graphical user interface (7). According to the invention, the signal-processing and control means (5) process the CO.sub.2 content measurement signals, to select the maximum CO.sub.2 content value (Vmax) during a given time period (dt), and to transmit this maximum value (Vmax) to the graphical user interface (7), which displays this maximum CO.sub.2 content value (Vmax).

Claims

1. A respiratory assistance apparatus for delivering a respiratory gas to a patient during cardiopulmonary resuscitation (CPR), comprising: a source (1) of respiratory gas for delivering a respiratory gas to said patient during cardiopulmonary resuscitation (CPR), a CO.sub.2 content measurement device (4) adapted to measure the CO.sub.2 content in order to perform measurements of the concentration of CO.sub.2 produced by said patient, and to supply CO.sub.2 content measurement signals to a signal-processing and control system (5), a signal-processing and control system (5) configured to process the CO.sub.2 content measurement signals originating from the CO.sub.2 content measurement device (4), at least one graphical user interface (7), wherein: the signal-processing and control system (5) is configured: a) to process the CO.sub.2 content measurement signals corresponding to measurements performed by the CO.sub.2 content measurement device (4) during a given time period (dt), and to extract therefrom a plurality of CO.sub.2 content values, b) to select the maximum CO.sub.2 content value (Vmax) from the plurality of CO.sub.2 content values measured during said given time period (dt), and c) to transmit said maximum CO.sub.2 content value (Vmax) to the graphical user interface (7), and wherein the graphical user interface (7) is configured to display the maximum CO.sub.2 content value (Vmax).

2. The apparatus according to claim 1, wherein the signal-processing and control system (5) comprises at least one microprocessor.

3. The apparatus according to claim 1, wherein the CO.sub.2 content measurement device (4) comprises a capnometer.

4. The apparatus according to claim 1, wherein a gas conduit (2) is in fluidic communication with a respiratory interface (3).

5. The apparatus according claim 1, wherein the CO.sub.2 content measurement device (4) is arranged: either upstream from and in immediate proximity (18) to a respiratory interface (3), or in the apparatus, being connected to a gas sampling site (18) situated upstream from and in immediate proximity to the respiratory interface (3).

6. The apparatus according to claim 1, wherein the given time period (dt) is between 2 and 10 seconds.

7. The apparatus according to claim 1, the CO.sub.2 content measurement device (4) is configured to perform measurements continuously.

8. The apparatus of claim 1, further comprising a storage device (8) cooperating with the signal-processing and control system (5) in order to store the plurality of CO.sub.2 content values measured during the given time period.

9. The apparatus according to claim 1, further comprising an alarm configured to trigger when the maximum CO.sub.2 content value exceeds a threshold value.

10. The apparatus according to claim 1, wherein the graphical user interface (GUI) comprises a digital screen.

11. The apparatus according to claim 1, wherein the signal-processing and control system (5) is configured to control the source (1) of respiratory gas and to deliver the respiratory gas in successive ventilatory cycles.

12. The apparatus according to claim 11, wherein the source (1) of respiratory gas comprises a motorized micro-blower.

13. The apparatus according to claim 1, wherein the graphical user interface (7) is configured to display the maximum CO.sub.2 content value (Vmax) in the form of a numerical value and/or a graphical representation.

14. The apparatus according to claim 1, wherein the CO.sub.2 content measurement device (4) is configured to perform successive measurements of the CO.sub.2 concentration over successive time periods (dt).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0115] The invention will now be better understood from the following detailed description given as a non-limiting example and with reference to the appended figures, in which:

[0116] FIG. 1 is a graphical representation of the variations of the CO.sub.2 content in the respiratory gases of a patient who is being ventilated and who is not in cardiac arrest,

[0117] FIG. 2 is a diagram showing a ventilatory cycle with two pressure levels that can be used by the apparatus of FIG. 6 in order to ventilate a patient in cardiopulmonary arrest during CPR,

[0118] FIG. 3 illustrates the pressure variations observed by the machine at the end of the respiratory circuit in the case of a patient in cardiopulmonary arrest during CPR,

[0119] FIG. 4 is a diagram showing the quantity of CO.sub.2 measured by the capnometer of the apparatus of FIG. 6 before and after a resumption of spontaneous cardiac activity,

[0120] FIG. 5 is a diagram showing the CO.sub.2 content peaks during the ventilatory cycles implemented during CPR, and

[0121] FIG. 6 is a diagram showing an embodiment of a respiratory assistance apparatus for CPR according to the invention.

[0122] FIG. 6 is a schematic representation of an embodiment of a respiratory assistance apparatus or medical ventilator according to the invention used for delivering a respiratory gas, typically air or oxygen-enriched air, to a patient P during cardiopulmonary resuscitation (CPR), that is to say to a person who is in cardiac arrest and on whom a first responder performs cardiac massage, that is to say an alternation of chest compressions (CC) and relaxations (Re), that is to say non-compressions.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0123] This apparatus or ventilator comprises a source 1 of respiratory gas, such as a motorized micro-blower, which is in fluidic communication with a gas conduit 2 for delivering a respiratory gas to said patient P during cardiopulmonary resuscitation, typically pressurized air.

[0124] The source 1 of respiratory gas is governed, that is to say controlled, by signal-processing and control means 5, in particular an electronic board with microprocessor 6 or similar. The signal-processing and control means 5 control the source 1 of respiratory gas in such a way that it delivers the gas in accordance with one or more predefined ventilation modes.

[0125] Preferably, the signal-processing and control means 5 make it possible to control the source 1 of respiratory gas so as to deliver the gas in accordance with a normal ventilatory mode, corresponding to ventilation of a patient who is not in cardiac arrest, and a CPR ventilatory mode, corresponding to ventilation of a patient who is in cardiac arrest and on whom a first responder initiates or performs CPR.

[0126] For example, in accordance with a ventilation mode intended for CPR, the source 1 of respiratory gas is controlled so as to deliver the respiratory gas, typically air, in a ventilatory cycle comprising several pressure levels or of the BiPAP type, as illustrated in FIG. 2, in particular two pressure levels comprising a low pressure level, for example a low pressure (LP) of between approximately 0 cm H.sub.2O and 15 cm H.sub.2O, and a high pressure level, for example a high pressure (HP) of between approximately 7 cm H.sub.2O and 40 cm H.sub.2O.

[0127] The gas is delivered alternately between these two pressure levels (LP, HP), as is illustrated in FIG. 2, throughout the CPR performed by the first responder, that is to say while the first responder performs the chest compressions and relaxations. The duration (D.sub.LP) of delivery of gas at low pressure (LP) by the micro-blower 1 is between 2 and 10 seconds, typically of the order of 3 to 6 seconds, whereas the duration (D.sub.HP) of delivery of gas at high pressure (HP) is less than 3 seconds, for example of the order of 0.5 to 1.5 seconds.

[0128] The micro-blower 1 of the ventilator generates two pressure levels, namely a high-pressure level (i.e. HP) and a low-pressure level (i.e. LP). The cardiac massage alternating between phases of chest compression (CC) and relaxation (Re) generates pressure peaks, which are superposed on the pressure cycles of the ventilator. This results, at the patient interface, in a pressure curve as illustrated in FIG. 3 where the pressure peaks at the high plateaus (i.e. at HP) and low plateaus (i.e. at LP) reflect the chest compressions (CC) with increased pressure, since the chest yields under the pressure of the CC performed by the first responder, and the relaxations (Re) with low pressure, since the chest rises again in the absence of CC.

[0129] As will be seen from FIGS. 2 and 3, in the context of the present invention the given time period (dt), during which the plurality of CO.sub.2 content values are measured and the maximum CO.sub.2 content value (Vmax) is extracted therefrom, corresponds to the duration (DLP) of delivery of gas at low pressure (LP), i.e. between 2 and 10 seconds, typically between 3 and 6 seconds.

[0130] The gas delivered by the micro-blower 1 is conveyed through the gas conduit 2 which forms all or part of the inhalation branch 2a of the patient circuit 2a, 2b. The respiratory gas, generally air, is delivered to the patient via a gas distribution interface 3, for example here an endotracheal intubation tube, more simply called a tracheal tube. However, other interfaces may be used, in particular a face mask or a laryngeal mask.

[0131] The gas conduit 2 is in fluidic communication with the gas distribution interface 3, such as a tracheal tube, in such a way as to supply the latter with the gas originating from the source 1 of respiratory gas, in this case a micro-blower. The gas conduit 2 will in fact be attached to the tracheal tube 3 by way of an intermediate attachment piece 8, here a Y-shaped piece. This Y-shaped intermediate attachment piece 8 comprises internal passages for gas.

[0132] The intermediate attachment piece 8, that is to say the Y-shaped piece, is likewise attached to the exhalation branch 2b of the patient circuit 2a, 2b so as to be able to collect and convey the gases rich in CO.sub.2 that are exhaled by the patient P and to discharge them to the atmosphere (at 9).

[0133] Also provided according to the invention are means 4 for measuring the CO.sub.2 content, called a CO.sub.2 sensor or capnometer, which means are designed to perform measurements of the concentration of CO.sub.2 in the gas exhaled by the patient P and to deliver CO.sub.2 content measurement signals to the signal-processing and control means 5, where these measurement signals can be processed, in particular by one or more calculation algorithms or similar.

[0134] In the embodiment in FIG. 6, the CO.sub.2 sensor is arranged near the mouth of the patient P in the mainstream configuration, that is to say upstream from and in immediate proximity to the respiratory interface 3, preferably between the intermediate attachment piece 8, i.e. the Y-shaped piece, and the respiratory interface 3, i.e. the tracheal tube, for example on a junction piece 18 (cf. FIG. 6).

[0135] According to another embodiment (not shown), the CO.sub.2 sensor can be arranged in the sidestream configuration. In this case, the CO.sub.2 sensor 4 is situated in the framework of the respiratory assistance apparatus and is connected, via a gas sampling line, such as tubing or the like, to a gas sampling site situated upstream from and in immediate proximity to the respiratory interface 3, for example on the junction piece 18. This gas sampling line communicates fluidically with the lumen of the junction piece 18 in such a way as to be able to collect a sample of the gas from there and convey it then to the CO.sub.2 sensor situated in the framework of the apparatus.

[0136] In all cases, the junction piece 18 comprises an internal passage for gas, allowing the gas to pass through it.

[0137] Preferably, the CO.sub.2 sensor performs continuous measurements of the concentration of CO.sub.2 in the gas flowing through the junction piece 18, which gas is enriched in CO.sub.2 during its passage through the lungs of the patient P, where gaseous exchanges take place.

[0138] The CO.sub.2 content measurement signals are then transmitted by the CO.sub.2 sensor to the signal-processing and control means 5 by an electrical connection or similar, in particular by wire or similar.

[0139] The monitoring of the CO.sub.2 content, in particular of the etCO.sub.2 which indirectly reflects the alveolar CO.sub.2 content, is in fact of great importance during CPR, especially for detecting a resumption of spontaneous cardiac activity (RSCA). This is because a resumption of spontaneous cardiac activity (RSCA), hence a significant increase of the cardiac output, brings about a rapid increase in the quantity of CO.sub.2 carried by the blood to the lungs and transferred through the alveolar-capillary membrane, this CO.sub.2 then being found again in the gas flow exhaled by the patient.

[0140] The signal-processing and control means 5 (in particular the microprocessor 6) are configured:

[0141] a) to process the CO.sub.2 content measurement signals corresponding to measurements performed by the CO.sub.2 content measurement means 4, typically the capnometer or CO.sub.2 sensor, during the given time period (dt), for example several seconds, in order to extract therefrom a plurality of CO.sub.2 content values.

[0142] b) to select the maximum CO.sub.2 content value (Vmax) from the plurality of CO.sub.2 content values measured during said given time period (dt), and

[0143] c) to transmit this maximum CO.sub.2 content value (Vmax) to a graphical user interface 7 or GUI.

[0144] A source 10 of electric current, such as a rechargeable battery or similar, directly or indirectly supplies electric current to the signal-processing and control means 5, the micro-blower 1, the GUI 7 or any other element of the apparatus, in particular a storage memory 11. The source 10 of electric current is preferably arranged in the framework of the ventilator.

[0145] Generally, the medical ventilator of the invention permits a continuous measurement of the concentration of CO.sub.2 produced by the patient P, the measurement being performed by the capnometer 4 which is arranged on the pathway of the gas, close to the mouth of the patient P, preferably here between the Y-shaped piece 8 and the tracheal tube 3 of FIG. 6, that is to say at the junction piece 18 attached fluidically between the Y-shaped piece 8 and the tube 3.

[0146] If so desired, the ventilator additionally permits parallel performance of a continuous measurement of the exhaled and inhaled gas flow rates, with the aid of one or more flow rate sensors (not shown).

[0147] According to the invention, the GUI for its part is configured to display the maximum CO.sub.2 content value supplied by the signal-processing and control means 5, which value is selected from several CO.sub.2 concentration values measured for a given duration corresponding to several successive chest compressions and relaxations performed by a first responder carrying out cardiac massage (i.e. CPR) on the patient P in cardiac arrest.

[0148] The reason is that the CO.sub.2 concentration value which best reflects the alveolar CO.sub.2 content, and which hence gives a good indication of the state of the blood flow in the patient P during the CPR, is the highest CO.sub.2 value, also called the maximum value (Vmax) or peak value, as illustrated in FIG. 5 which shows the development of the CO.sub.2 content in the gas and illustrates several etCO.sub.2 measurements for several successive durations (dt), for example durations of 3 to 6 seconds, while CPR is being performed. It will be seen here that the CO.sub.2 content of the gas is not constant during a given time interval dt and that there is therefore necessarily a maximum CO.sub.2 content value (Vmax) over each interval dt, that is to say the peak value.

[0149] Hence, in the context of the present invention, the ventilator thus stores (at 11) all the peak values of CO.sub.2 during each time period dt, typically between 3 and 7 seconds, and determines the maximum CO.sub.2 content value (Vmax) from the plurality of peaks (EtCO2.sub.1, EtCO2.sub.2, EtCO2.sub.3, . . . , EtCO2.sub.x) measured over a given time period, as is illustrated in FIG. 5.

[0150] During CPR, the CO.sub.2 content in the gas produced by the patient, and passing the measurement tap of the capnometer 4, varies depending on the presence or absence of chest compressions (CC).

[0151] Thus, after insufflation of air by the micro-blower 1 of the ventilator and as long as chest compression has not commenced, no CO.sub.2 is detected in the gas flows passing through the conduit 2 as far as the respiratory interface 3, which then distributes this air to the lungs of the patient P.

[0152] After several chest compressions (CC) performed by a first responder, CO2 is detected at the Y-shaped piece 8 by the capnometer 4 since the alternations of chest compressions (CT) and relaxations (Re) generate movements of air entering and leaving the lungs of the patient P by imitating the exhalation phases of the patient P. Exhaled air rich in CO.sub.2 is then found again at the Y-shaped piece 8 and the capnometer 4 (cf FIG. 6), and measurements of the CO.sub.2 concentrations can be performed by the capnometer 4. The corresponding measurement signals are sent to the signal-processing and control means 5 where they are processed in the way explained above, so as to determine the maximum CO.sub.2 content value (Vmax) over each time interval dt.

[0153] The maximum CO.sub.2 value (Vmax) is the one that best represents the alveolar CO.sub.2. In fact, the CO.sub.2 present at the Y-shaped piece 8 and the capnometer 4 is washed out little by little on account of the successive and repeated chest compressions and tends to decrease after reaching this maximum value, since the chest compressions thus cause the discharge to the atmosphere (at 9) of the gases rich in CO.sub.2, via the exhalation branch 2b of the patient circuit. The successive chest compressions (CC) thus generate different levels of CO.sub.2, the most representative one being the peak value or maximum value (Vmax), as is illustrated in FIG. 5.

[0154] In the context of the present invention, the ventilator thus stores (at 11) all the maximum CO.sub.2 content values (Vmax) between two ventilatory cycles, that is to say during the successive durations dt, determines the maximum CO.sub.2 content value (Vmax) from the plurality of maximum values measured, and displays this maximum value (Vmax) on the screen of the GUI 7.

[0155] This maximum value (Vmax), during a given time interval dt, can be displayed as a single numerical value. It is also possible to display several maximum values (Vmax) measured successively over several successive time intervals (dt). Furthermore, if it is deemed useful or desirable, it is also possible to display the value in the form of a graphical representation showing several maximum values (Vmax) measured successively over several successive time intervals (dt) over the course of time, for example over the last 2 to 5 minutes, for example a graphical representation such as a curve, bar graph or similar.

[0156] The data calculated from these CO.sub.2 measurements allow the first responder to better control the CPR, by virtue of an indicator which reflects the state of the circulation and metabolism of the patient since, at a constant ventilation level, the more effective the CPR, the greater the quantity of CO.sub.2 produced and transferred through the alveolar-capillary membrane, hence the greater the quantity of CO.sub.2 that can be detected at the capnometer 4.

[0157] Hence, in the case of a resumption of spontaneous cardiac activity (RSCA), the circulation recovers abruptly and therefore the quantity of alveolar CO.sub.2 increases in parallel, which induces a substantial increase in the quantity of CO.sub.2 detected by the capnometer 4 by a factor often greater than 2, as is illustrated in FIG. 4. It will in fact be seen from FIG. 4 that the etCO.sub.2 is always below 25 KPa during the CPR, whereas the etCO.sub.2 increases suddenly to reach over 50 KPa in the event of resumption of spontaneous cardiac activity (RSCA). This can be immediately detected by the first responder, who can then carry out an analysis of the heart rhythm in order to stop cardiac massage in the case of effective RSCA.

[0158] To put it another way, in the context of the invention, the fact that the GUI 7 displays the maximum etCO.sub.2 value, during a given time period (dt), allows the first responder to better detect the occurrence of an RSCA since this maximum CO.sub.2 value (Vmax) closely reflects the alveolar CO.sub.2.

[0159] It has in fact been found, in tests carried out in the context of the present invention, that continuously displaying all the CO.sub.2 measurements would not be effective, since the cardiac massage itself, even when carried out uniformly (pressure force, frequency, etc.), inevitably causes considerable variations in CO.sub.2 content at the capnometer from one chest compression to another. This is explained by the dynamic behaviour or opening/closing of the small airways and by the effect of lavage of the dead space during the successive chest compressions between two machine cycles. Therefore, displaying all the CO.sub.2 measurements could cause the first responder to make an error or could drown him under too much information, and he could then sometimes believe there was a resumption of spontaneous cardiac activity even when it was only an artefact, or, conversely, the first responder could fail to notice a resumption of spontaneous cardiac activity (RSCA) in the patient and could continue the massage when the patient is in the RSCA phase. In all cases, the use of a single instantaneous value for prognostic reasons or for choice of therapeutic strategy is made risky by the oscillating nature of the instantaneous etCO2 value, i.e. at each chest compression (CC).

[0160] In the context of the invention, it has been shown in practical tests that these problems could be completely overcome by displaying only the highest CO.sub.2 content value (Vmax) during a given time period (dt), typically of a few seconds.

[0161] In addition, it has been found that the CO.sub.2 content measured at each chest compression can vary enormously from one chest compression to another. This is due not only to the anatomical and instrumental dead space but also to the degree of opening of the patient's airways. Taking these factors into account, the maximum CO.sub.2 content value (Vmax) appears therefore to be a better reflection of the alveolar CO.sub.2 and is thus a good indicator of RSCA (if it increases abruptly) or of a new cardiac arrest (if its decreases abruptly), which informs the first responder immediately and in a more relevant way.

[0162] Thus, when the first responder notes a strong increase in the displayed CO.sub.2 value, he can conclude from this that the patient is in the RSCA phase, as is illustrated in FIG. 4, and can then decide to stop the cardiac massage in order to carry out an analysis of the heart rhythm for example.

[0163] Advantageously, the ventilator of the invention can also include alarm means designed and programmed to warn the first responder or the like when the measured maximum CO.sub.2 value exceeds or, conversely, drops below a given value that is predefined or calculated continuously.

[0164] In particular, an acoustic and/or visual alarm is provided which triggers when the maximum CO.sub.2 content measured, at a time t, is greater than a threshold value, for example: [VmaxCO.sub.2]>1.5[MeanCO.sub.2] where: [0165] [VmaxCO.sub.2] is the maximum CO.sub.2 content value measured during a given duration dt, for example over a duration dt of between 2 and 10 seconds, [0166] .[MeanCO.sub.2] is the mean value of the maximum CO.sub.2 content values [VmaxCO.sub.2] determined for several successive durations dt in a given time window (FT) (FT>x.dt with x2), for example a period of 30 seconds to 5 minutes, or more.

[0167] Similarly, the alarm can trigger in the event of the CO.sub.2 concentration dropping abruptly below a given minimum value, which could be the sign of a new cardiac arrest of the patient, of hyperventilation, or of obstruction of the gas circuit between the patient and the machine, for example a flexible conduit that is bent or crushed and no longer allows the gas to pass through.

[0168] Generally, the invention relates to a medical ventilator suitable for use during cardiopulmonary resuscitation (CPR), comprising a source 1 of respiratory gas, such as a micro-blower, means 4 for measuring the CO.sub.2 content, such as a capnometer, signal-processing and control means 5 receiving and processing the CO.sub.2 content measurement signals originating from the CO.sub.2 content measurement means 4, and a GUI 7 configured to display at least one maximum CO.sub.2 content value (Vmax) measured during a given time period (dt), said maximum CO.sub.2 content value (Vmax) being selected from a plurality of CO.sub.2 content values measured during said given time period (dt).

[0169] The respiratory assistance apparatus or medical ventilator according to the present invention is particularly suitable for use during cardiopulmonary resuscitation (CPR) on a person (i.e. a patient) in cardiopulmonary arrest, in the context of which a respiratory gas such as pressurized air is supplied, in accordance with a ventilatory cycle with several pressure levels, to said person undergoing the cardiac massage with alternating chest compressions and relaxations. To facilitate its transport by the first aid responders, for example by a physician, a nurse, a fire fighter or similar, the ventilator of the invention is preferably arranged in a bag for carrying it.

[0170] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.