FR3066120A1 - RESPIRATORY ASSISTANCE APPARATUS WITH INSPIRED OXYGEN FRACTION ESTIMATION - Google Patents

Abstract

The invention relates to a respiratory assistance apparatus comprising a first gas source (2) and a gas circuit (3), said first gas source (2) being fluidly connected to the gas circuit (3) for delivery therein a gas flow, characterized in that it further comprises means for adding gas (12, 14) fluidly connected to the gas circuit (3) to operate an addition to the gas flow, a first gas containing oxygen at a fixed first rate (QO2), at an addition site (13) of said gas circuit (3) and obtaining a main flow of gas at a total gas flow (Qtot), measuring means of flow rate (8) arranged to measure the total gas flow (Qtot) of the main flow of gas flowing in the gas circuit (3), and control means (10) configured to calculate the inspired oxygen fraction (FiO2) in the main flow of gas, at the site of addition of the gas circuit (13), from the total gas flow (Qtot) of the main flow of gas measured by the flow measuring means (8) and the first fixed flow rate (QO2). A method for determining the inspired oxygen fraction (FiO2) of a main flow of gas flowing through a gas circuit of such a respirator.

Description

The invention relates to a method for determining, in real time, the fraction of inspired oxygen (FiO2) in a gas flow containing a variable oxygen content, typically oxygen-enriched air, circulating in an assistance device. respiratory, and such a medical device implementing this method, usable in home ventilation of non-dependent patients.

In the context of home ventilation, in particular for a non-dependent patient, it is sometimes necessary to administer to the patient air enriched with oxygen (O2), that is to say containing more 22% oxygen (% in vol.), Using a medical respiratory assistance device, commonly called a ventilator, delivering the respiratory flow of oxygen-enriched air to said patient. The addition of an oxygen flow (or an oxygen-rich gas) to the air flow delivered for example by a motorized micro-blower, is done in the gas circuit of the device.

In order to ensure that the air / oxygen mixture is done correctly and / or that the air / oxygen mixture intended for the patient contains an adequate proportion of oxygen, it is necessary to be able to know, preferably continuously and / or in time the oxygen content of the gas flow circulating in the device.

Now measure the fraction of inspired oxygen (FiO2), i.e. the proportion of gaseous oxygen contained in the oxygen-enriched gas, typically air with oxygen added, which circulates in the circuit gas from the appliance, is complicated.

To do this, a chemical cell type sensor can be used. However, by its very nature, such a sensor is not ideal. Indeed, the oxygen in the air / O2 mixture to which the sensor is exposed gives rise, inside the latter's chemical cell, to a chemical reaction producing an electrical voltage proportional to the amount of oxygen present in the mixture . However, this chemical reaction depends on the temperature of the reactants and their respective concentrations. These sensors are therefore sensitive to many parameters, in particular to the initial concentrations of the reagents, to the duration of use of the sensor, to the way in which the sensor is exposed to the air / oxygen flow, to the concentrations to which the sensor is exposed during its life cycle, at the temperature of the mixture, at room temperature ... This therefore results in a great disparity in the measurements carried out by chemical cells for measuring oxygen concentration for the same given gas flow, even when these are new, for the same cell model and / or belonging to the same batch.

Therefore, to operate reliable and quality measurements, it would be necessary to calibrate the sensors before each use and to take into account the characteristics of each sensor. However, it is easy to understand that such a systematic calibration is tedious and impractical, even completely unthinkable in the context of home care of a patient. In addition, another drawback of these sensors is their response time, that is to say their "measurement inertia". Indeed, even if the sensor is used in optimal conditions, its response time generally remains greater than 5 seconds, or even 10 seconds. Knowing that the duration of an inspiration is of the order of 1 to 2 seconds, it is understandable that the measurement of oxygen concentration provided by a chemical cell cannot reach a satisfactory precision to be interpretable on the medical level.

In addition, it has also been proposed to use paramagnetic or zirconium oxide sensors. However, in practice, it has been found that these types of sensors are not adapted to the problems of home ventilation of patients because they are very expensive and / or too energy consuming.

The problem that arises is therefore to propose a process making it possible to determine, in real time and / or continuously, the fraction of inspired oxygen (FiCF), that is to say the proportion of oxygen (% in vol.), in a gas stream containing a variable oxygen content, typically a stream of oxygen-enriched air, circulating within a ventilator or respiratory assistance device, in particular an appliance intended to be used in the context ventilation in the home of non-dependent patients, reliably, precisely, at a reasonable cost and without generating excessive energy consumption, as well as a respiratory assistance device implementing such a process.

A solution of the invention is then a method for determining the fraction of inspired oxygen (F1O2), or proportion of oxygen, of a main flow of gas circulating within a gas circuit of an apparatus for respiratory assistance, in which: a) a main gas flow is produced by mixing a first gas containing oxygen with a second gas within the gas circuit of the respiratory assistance apparatus, said first gas containing oxygen being added at a first flow rate (Q02) fixed at a site for adding said gas circuit, b) the total gas flow rate (Qtot) of the main gas flow obtained in step a) and circulating is measured in the gas circuit, and c) the fraction of inspired oxygen (FiO2) in the main gas flow, at the gas circuit addition site, is calculated from the total gas flow (Qtot) of the main flow of gas measured in step b) and the first flow rate (Q02) fixed.

Depending on the case, the method of the invention may include one or more of the following technical characteristics: - in step b), the total gas flow (Qtot) of the main gas flow is measured in real time, preferably continuously. - it also includes a display step, as a function of time, of the inspired oxygen fraction (FiO2) calculated in step c) or of an indicator representative of the inspired oxygen fraction (FiO2) in step c). - the display step implements a data visualization screen. - prior to step c), it also includes a step making it possible to indicate or fix the value of the first flow rate (Q02) of the first gas containing oxygen. During this step, the desired value of the first flow (Q02) is set by the user and entered into the device by means of a man / machine interface, for example keys, buttons ... - the first gas containing oxygen is gaseous oxygen. - the second gas is air. - the main gas flow consists of air with added oxygen. - the second gas is delivered by a motorized micro-blower, that is to say equipped with an electric motor, which delivers air into the appliance's gas circuit. - in step c), the fraction of inspired oxygen FiO2 (expressed in%) is calculated using the following formula: FiO2 = 21 + 79. (Qo2 / Qtot) - in step b), we measure the total gas flow (Qtot) of the main gas flow by means of a flow sensor arranged in the gas circuit downstream from the site of addition of the first gas containing oxygen. - in step b), the total gas flow (Qtot) of the main gas flow is measured by means of a flow sensor. - in step b), a flow sensor of the hot wire, differential pressure, pressure drop, Venturi effect or other type is used. - in step a), the first gas containing oxygen at a constant flow rate is introduced into the flow of the second gas in the gas circuit. - in step a), the first oxygen-containing gas comes from a gas container-type gas source which feeds the gas circuit of the appliance at the desired addition site so as to operate the mixing between said first oxygen-containing gas and the second gas, typically a mixture of oxygen and air, respectively. - in step a), the first oxygen-containing gas comes from a pressurized gas cylinder, a pressurized gas container or an oxygen concentrator. - in step a), the first oxygen-containing gas comes from a gas source containing the gas in gaseous and / or liquefied form. The invention also relates to a respiratory assistance device comprising a first gas source and a gas circuit, said first gas source being fluidly connected to the gas circuit to deliver a gas flow therein, characterized in that it further includes: - gas addition means fluidly connected to the gas circuit for adding to the gas flow, a first gas containing oxygen at a first fixed flow rate (Q02), at a site d adding said gas circuit and obtaining a main gas flow at a total gas flow (Qtot), - flow measurement means arranged to measure the total gas flow (Qtot) of the main gas flow circulating in the gas circuit , and - control means configured to calculate the fraction of inspired oxygen (F1O2) in the main gas flow, at the gas circuit addition site, from the total gas flow (Qtot) of the main gas flow measured by m means for measuring the flow and the first flow (Q02) fixed.

Depending on the case, the respiratory assistance device according to the invention may comprise one or more of the following technical characteristics: - the first source of gas is a source of air, - the first source of gas is a micro- blower. - the first source of gas is a motorized micro-blower, that is to say one equipped with an electric motor. - The micro-blower delivers a flow of a second gas containing air, preferably a flow of air. - The first source of gas is a motorized micro-blower controlled by the control means. - The flow measurement means comprise a flow sensor. - The gas addition means comprise a gas pipe and / or a valve, preferably the valve is controlled by the control means. - The control means include an electronic microprocessor card. - It further comprises a pressure sensor is arranged on the gas circuit, preferably said pressure sensor is connected to the control means. - It further comprises a solenoid valve arranged on the gas circuit between the first source of gas and the addition site, said solenoid valve being controlled by the control means so as to control the flow and / or pressure of gas in the gas circuit. - The gas addition means are supplied by a second source of gas containing oxygen, preferably an oxygen cylinder or an oxygen pipeline. - the micro-blower, the gas circuit, the flow measurement means making it possible to measure the total gas flow (Qtot) of the main flow of gas circulating in the gas circuit, and the control means are arranged in a rigid carcass . In general, the solution of the invention is based on a real-time measurement, by a flow sensor, of the total gas flow (Qtot) of the main gas flow, typically an air flow / 02, within a given measurement site in the fan gas circuit and the use of this measured value of the total gas flow (Qtot) and the value of the first flow (Q02) of the first gas containing oxygen, typically a flow of oxygen prescribed to the patient and which is generally entered into the ventilator by the user, via a man-machine interface, for example via an input on a digital screen or a keyboard, so as to estimate the fraction of inspired oxygen (F1O2) in the main gas flow, at the gas circuit addition site, in particular by performing the following calculation: F1O2 = 21 + 79. (Qo2 / Qtot) (expressed in% by vol).

Thus, it is possible to obtain an estimate as precise as possible of the fraction of CF (F1O2) of the gas circulating in the ventilator, for example of air enriched in oxygen to be inhaled by a patient, without having to use a fraction sensor. of chemical cell type CF or an expensive sensor such as paramagnetic or zirconium oxide.

It may also result from numerous parameters of the ventilation administered, such as the quantity of CF inspired, the value of average CF at the entry of the respiratory tract of the patient in inspiration, over a cycle and any other indicator useful for the administration of appropriate and effective treatment to the ventilated patient.

In fact, the flow of O2 introduced into the air circuit of the respiratory assistance device is generally constant since it corresponds to a value entered by the user on a man-machine interface of the device, such as a digital touch screen or one, or adjustment keys, sliders or rotary knobs ...

Likewise, the location of the site or point of addition of O2 in the appliance's gas circuit is known.

Finally, the gas pressure in the gas circuit is assumed to be constant and positive, typically about 1 to 5 bar higher than atmospheric pressure.

However, it is known that once the gas mixture has operated in step a), typically a mixture of air and O2, at the point of addition of the appliance gas circuit, there is no no re-mixing inside the gas circuit of the ventilatory assistance device.

From there, the fact of being able to determine the oxygen content at the addition site by means of the process of the invention described above, implemented in the apparatus of the invention, makes it possible to estimate the FiO2 at any point of the circuit. gas. The invention will now be better understood thanks to the following detailed description, given by way of illustration but not limitation, with reference to the appended figures among which: - Figure 1 is a diagram of an embodiment of an apparatus for respiratory assistance according to the present invention, - Figure 2 is a representation of the flow rates Q tot and Qpatient, where Q tot is the measurement of the total gas flow (flow rate of oxygen and air mixture) delivered by the respiratory assistance and Q_patient is the estimated patient flow. - Figure 3 is a diagram of the inputs / outputs of the circuit which makes it possible to characterize the direction of flow in the patient circuit during a cycle. - Figure 4 is a representation of the different phases of a respiratory cycle.

Fa Figure 1 is a schematic representation of an embodiment of a respiratory assistance device 1 or ventilator according to the present invention.

It comprises a first source of gas 2, namely a motorized micro-blower, that is to say one equipped with an electric motor driving a paddle wheel, here delivering an air flow (oxygen content 21% in vol.) in a gas circuit 3 in fluid communication with the air outlet 2a of the micro-blower 2. The air coming from the micro-blower 2 is conveyed by the gas circuit 3 to a humidifier of gas 4 located downstream of the device 1, before being conveyed to a patient 20 via a flexible gas conduit 5, to which it is administered by means of a respiratory interface 6, such as a nasal or facial mask.

A pressure sensor 7 and a flow sensor 8 are arranged on the gas circuit 3, downstream of the micro-blower 2, to measure therein the pressure P and the flow rate Q tot of the gas flowing therein.

In addition, optionally, a piloted valve 9 is arranged on the gas circuit 3, downstream of the micro-blower 2 and upstream of the pressure 7 and flow rate sensors 8, so as to control the gas flows in the gas circuit 3.

Control means 10 typically comprising an electronic card comprising a microprocessor, such as a microcontroller, implementing at least one algorithm, receives the measurements (i.e. signals) operated by the pressure and flow sensors.

The control means 10 control the motorized micro-blower 2 delivering the air flow in the gas circuit 3 and possibly the piloted valve 9 so as to deliver a gas flow and / or pressure according to the modes of ventilation mode selected by the doctor, which modes and modalities are for example informed by means of adjustment buttons and / or a touch screen.

The control means 10 receive information (ie signals) relating to the characteristics of the gas flow present in the circuit 3, namely the pressure of the gas flow measured by the pressure sensor 7 and the flow rate of the gas flow measured by the flow sensor 8.

The components of the device 1, in particular the motorized micro-blower 2, the pressure 7 and flow rate sensors 8, at least part of the gas circuit 3 and the piloted valve 9 and the piloting means 10 are arranged in a cowling 15 acting as the external carcass of the device 1.

Furthermore, a second source 11 of gas containing oxygen or "oxygen-rich gas", namely here an oxygen cylinder or an oxygen pipe, is fluidly connected to the gas circuit 3 of the device 1 , via one or more gas conduits 12, so as to introduce into the air flow circulating in the gas circuit 3 of the device 1, the additional oxygen-rich gas, for example pure oxygen (content of 100% oxygen in vol.). The supply of oxygen-rich gas is controlled by a valve 14 arranged on the gas conduit 12. The user determines the characteristics such as flow rate and / or pressure of the oxygen-rich gas.

The control means 10 control the valve 14 controlling the arrival of the oxygen-rich gas in the gas circuit 3 so as to deliver into the gas circuit, said oxygen-rich gas in the appropriate circumstances, preferably only during the phases ventilation but not during the phases when the device is not used).

In another embodiment, the supply of oxygen-rich gas is not controlled by a valve on the gas pipe, but controlled by the user who determines the presence or absence and the characteristics such as flow and / or pressure. The oxygen-rich gas is introduced at an addition site 13 located upstream and in the immediate vicinity of the pressure 7 and flow rate sensors 8.

In another embodiment, the introduction of the oxygen-rich gas can be done at an addition site upstream of the turbine or at the air outlet 2a of the micro-blower. The oxygen-rich gas is introduced into the device 1 at the known and / or fixed rate Q02. The device also includes information input means (not shown), that is to say a man-machine interface, for example keys, rotary or translative buttons or the like, allowing the user to enter information in the device, such as the first flow (Q02) of the oxygen-containing gas which is added to the air flow delivered by the micro-blower 2.

Preferably, the device 1 comprises a digital display screen making it possible not only to display different information, data, pictograms, graphs, etc., but also to enter or enter data in the device 1 for their use. , in particular by the control means 10 or any other data processing means.

Alternatively, the micro-blower 2 can be replaced by a source of pressurized gas, external to the appliance 1, fluidly connected to the gas circuit 3 by a gas pipe. A solenoid valve 9 installed on the gas circuit 3 is controlled by the control means 10 for the purpose of delivering a gas flow and / or pressure according to the methods of the ventilation mode selected by the doctor.

In the context of the invention, it is necessary to know the differences between the flow measured by the flow sensor 8 of the device 1 (Q tot) and the patient flow (Q_patient) which corresponds to the flow of the gas flow actually exchanged with the patient, i.e. the flow of gas that has entered his airways.

In the case of single-leak ventilation, the patient flow (Q_patient) is not measured by the device 1 but can be estimated using information from the measured flow (Q tot) and the machine pressure (P) from pressure sensor (s) 7 using for example one of the algorithms described in EP 2 826 511 B1, EP 0 929 336 B1, WO 2017/006253 A1 or any other algorithm.

Figure 2 is a representation of the measured (Q tot) and patient (Q patient) flow rates during a few breaths expressed in liters per second.

The difference between Q tot and Q_patient comes from the flow lost in the leak located in the patient mask 6 and from the flow QOz of O2 addition. Here, the O2 addition rate (Qo2) is fixed, i.e. here equal to 5 L / min and the leak rate (Qf) is known.

Each respiratory cycle of patient 20 is broken down into three phases: inspiration, expiration "with reflux" and expiration "with washing".

Figure 3 schematically illustrates the gas inlets and outlets of the air circuit 3 and makes it possible to characterize the direction of flow in the patient circuit 3 during a cycle.

The flow Qo2 is the flow at which the oxygen-rich gas is added to the gas circuit 3.

The flow Qm is the flow of the gas flow generated by the micro-blower 2, in the circuit 3 before mixing with the oxygen-rich gas. The flow Q tot measured by the flow sensor 8 of the device 1 is the sum of the flows Qm and QOz.

The flow Qp is the flow of the gas flow actually exchanged with the patient, that is to say the gas flow which has entered its airways.

The flow rate Qf is the flow rate of the gas flow which passes through the leak located in the mask 6 of the patient.

By a material balance applied to the air circuit, we determine the direction of flow in the patient circuit.

During the inspiration phase, the air + O2 mixture flows from the machine to the patient circuit. The time τρ taken by the mixture to reach the patient is a function of the flow rate in the tube (Qm + Qq2) and the volume V considered for the air circuit.

Volume V represents the added volumes of the patient circuit and the mask. During this phase, at a given time t, the time τρ (t) taken by the mixture to reach the patient is given by:

Figure 4 is a representation of the flow Q tot measured by the flow sensor 8 during 2 respiratory cycles.

During the expiration phases, two regimes are to be distinguished, they start respectively at times t! and t2 materialized on the curve of Figure 4.

During the "reflux" expiration phase, the patient's exhalation rate is high and causes an accumulation of exhaled air in the patient circuit. In fact, a negative flow (—Qp - Qf), that is to say from the patient towards the machine, is observed in the patient circuit. During this phase, the mixture approaching the patient is forced back and expelled upstream of the flow sensor. At any time t of the expiration phase "with reflux", the volume of expired air back into the patient circuit is given by the relation:

We find in the integral the patient flow from which we subtract the flow of the leak materializing the exhaled air escaping directly through the mask. During this phase of the respiratory cycles, the fraction of O2 in the patient's mouth is that of the exhaled air (which we are not studying here) while at the machine level there is a "return to back ". Indeed, the reflux imposed by the exhalation pushes the mixture back and causes the loss of a volume Vreflux (t) of air + O2 mixture recently created.

The "backtrack" imposed on the mixture by expiration can be characterized by the duration rm which can be defined at any time t of this phase by the relation:

During the expiration phase "with washing", the patient's exhalation rate has decreased enough for the mask leak to be sufficient to evacuate the exhaled air.

Thus, the flow of mixture in the patient circuit becomes positive again and makes it possible to "wash" the patient circuit of the exhaled air accumulated in the first part of exhalation.

The patient circuit is washed at time tlav when the following relationship is satisfied:

From this time tlav, the air mixture in the mask is again a "fresh" air + O2 mixture.

The equations presented above are the building blocks of a model implemented in Excel from simulations and in order to show the feasibility of the algorithm.

They are given in the table below along with other modeling elements.

Board

In this table, F £% (t) and Fg2% (t) are the fractions of O2 respectively to the patient and to the machine (i.e. at the mixing point). The delays rm and τρ allow the values of Fq2% and Fq2Ü / o to be defined during the different phases of the ventilation cycle.

Finally, when the flow in the patient circuit is positive, we find the "classic" O2 fraction calculation function, namely:

The method described above makes it possible to calculate in real time and continuously F £% (t) which corresponds to the fraction of oxygen inspired by the patient (FiO2) without using any O2 measurement sensor in the context of reliable single-line leakage ventilation.

The method and the medical device or ventilator of the invention make it possible to determine, in real time, the fraction of inspired oxygen (FiO2) in a gas flow containing a variable oxygen content, typically air enriched with oxygen, circulating in a gas circuit, which can be used in home ventilation treatment, in particular of non-dependent patients to whom it is necessary to administer oxygen contents greater than 22% by volume.

Claims (15)

claims 1. Method for determining the inspired oxygen fraction (F1O2) of a main flow of gas circulating within a gas circuit of a respiratory assistance device, in which: a) a main flow of gas by mixing a first gas containing oxygen with a second gas within the gas circuit of the respiratory assistance device, said first gas containing oxygen being added at a first fixed rate (Q02) , at an addition site of said gas circuit, b) the total gas flow (Qtot) of the main gas flow obtained in step a) and flowing in the gas circuit is measured, and c) the fraction is calculated inspired oxygen (F1O2) in the main gas flow, at the gas circuit addition site, from the total gas flow (Qtot) of the main gas flow measured in step b) and the first flow ( Q02) fixed. 2. Method according to the preceding claim, characterized in that it further comprises a display step, as a function of time, of the inspired oxygen fraction (F1O2) calculated in step c) or of an indicator representative of the inspired oxygen fraction (F1O2) calculated in step c). 3. Method according to one of the preceding claims, characterized in that, prior to step c), it further comprises a step making it possible to indicate or fix the value of the first flow rate (Q02) of the first gas containing l 'oxygen. 4. Method according to one of the preceding claims, characterized in that: - the first gas containing oxygen is gaseous oxygen, - the second gas is air and - the main gas flow is formed of air with added oxygen. 5. Method according to one of the preceding claims, characterized in that the second gas is delivered by a motorized micro-blower. 6. Method according to one of the preceding claims, characterized in that in step c), the inspired oxygen fraction (FiO2) (expressed in%) is calculated using the following formula: FiO2 = 21 + 79. (Qo2 / Qtot) 7. Method according to one of the preceding claims, characterized in that in step b), the total gas flow (Qtot) of the main gas flow is measured by means of a flow sensor arranged in the gas circuit downstream from the site of addition of the first oxygen-containing gas. 8. Respiratory assistance apparatus comprising a first gas source (2) and a gas circuit (3), said first gas source (2) being fluidly connected to the gas circuit (3) to deliver a gas flow therein. , characterized in that it further comprises: - gas addition means (12, 14) fluidly connected to the gas circuit (3) to effect an addition to the gas flow, of a first gas containing l oxygen at a first flow rate (Q02) fixed, at an addition site (13) of said gas circuit (3) and obtain a main flow of gas at a total gas flow rate (Qtot), - flow measurement means (8) arranged to measure the total gas flow (Qtot) of the main flow of gas circulating in the gas circuit (3), and - control means (10) configured to calculate the fraction of inspired oxygen (FiO2) in the main gas flow, at the gas circuit addition site (13), from the total gas flow (Qtot) of the main flow l of gas measured by the flow measurement means (8) and of the first flow (Q02) fixed. 9. Respiratory assistance device according to claim 8, characterized in that the first source of gas (2) is a micro-blower, preferably the micro-blower delivers a flow of a second gas containing air. 10. Respiratory assistance device according to claim 8, characterized in that the flow measurement means (8) comprise a flow sensor. 11. Respiratory assistance device according to claim 8, characterized in that the gas addition means (12, 14) comprise a gas line (12) and / or a valve (14), preferably the valve ( 14) is controlled by the control means (10). 12. Respiratory assistance device according to claim 8, characterized in that the control means (10) comprise an electronic card with microprocessor. 13. Respiratory assistance device according to claim 8, characterized in that it further comprises a pressure sensor (7) is arranged on the gas circuit (13), preferably said pressure sensor (7) is connected to the steering means (10). 14. Respiratory assistance device according to claim 8, characterized in that it further comprises a solenoid valve (9) arranged on the gas circuit (3) between the first gas source (2) and the addition site (13), said solenoid valve (9) being controlled by the control means (10) so as to control the flow and / or pressure of gas in the gas circuit (3). 15. Respiratory assistance device according to claim 8, characterized in that the gas addition means (12, 14) are supplied by a second source (11) of gas containing oxygen, preferably a bottle of or an oxygen pipeline.