Medical ventilator with display indicating the recruitability of a patient's lungs

Abstract

Title of the Invention: Medical Ventilator with Display of a Patient's Lung Recruitability Indicator. The invention relates to a medical ventilator (1) comprising a gas circuit (2), flow measurement means (6) and pressure measurement means (5), a PEEP valve (12) arranged on the expiratory limb (2-2) of the gas circuit (2), a graphic display (8), and microprocessor-controlled control means (7-1) cooperating with the flow measurement means (6), the pressure measurement means (5), the PEEP valve (12), and the graphic display (8). The control means (7) are configured to determine an RI ratio from the flow and pressure measurements taken by the flow measurement means (6) and the pressure measurement means (5) and to display the calculated RI ratio on the graphic display (8). Abstract Figure: Fig. 1

Description

Title of the invention: Medical ventilator with display of an indication of the recruitability of a patient's lungs

[0001] The invention relates to a medical ventilator, i.e. a respiratory assistance device, making it possible to provide a real-time clinical diagnosis of a ventilated patient suffering from respiratory distress, i.e. ARDS, in the form of a recruitability index of the lungs of the patient in question, namely a re-recruitment / inflation ratio or recruitability ratio, called RI ratio.

[0002] Acute respiratory distress syndrome or ARDS is a common cause of death in humans. ARDS is characterized by severe lung damage, of which only a small portion can be recruited, i.e., ventilated and able to participate in pulmonary gas exchange, namely the supply of inspired oxygen (O2) and the elimination of expired carbon dioxide (CO2). Patients with ARDS have what are called "baby lungs."

[0003] Ventilatory management of ARDS requires the application of so-called "protective" ventilation, as well as personalization of the ventilatory parameters to adapt them to the patient in question.

[0004] Thus, an increase in positive end-expiratory pressure or PEEP (also called PEEP in English for Positive End-Expiratory Pressure) compared to a previously set PEEP level can allow an additional part of the lungs to be recruited, that is to say, to open parts of the lung which were not participating in gas exchange before the application of this PEEP. However, too high a PEEP could also distend a part of the lungs and be harmful to the patient.

[0005] According to a common definition, PEEP can be defined as the residual gas pressure maintained above atmospheric pressure, in the airways of a person, i.e. a patient, at the end of expiration. PEEP allows ventilation of the pulmonary alveoli which could be collapsed and, in general, allows increasing pulmonary gas exchange and reducing the patient's respiratory work.

[0006] The ability to recruit the lungs by increasing PEEP depends on the individuals, i.e. the patients to be treated. We thus distinguish: - so-called "recruiter" patients for whom an increase in PEEP allows an additional part of the lungs to be recruited. This recruitment, when effective, improves gas exchange and proves beneficial for patients. - so-called “non-recruiting” patients for whom an increase in PEP does not does not allow an additional part of the lungs to be recruited and can even be harmful to the patient since it can lead in particular to distension of the lungs, hemodynamic instability, etc.

[0007] It is therefore understood that it is essential to be able to assess the recruitability of each patient in order to personalize their ventilation, in particular the PEEP setting to be applied to them, to ensure effective ventilation of the patient and avoid harmful ventilation if the patient is not a recruiter.

[0008] Although different methods have been proposed to determine the PEEP setting, for example the multiple pressure / volume curve method, the use of electro-impedance tomography (EIT), the adaptation of the PEEP according to the value of the inspired oxygen fraction (FiO2) set on the ventilator or according to the patient's respiratory mechanics (i.e. driving pressure, plateau pressure, etc.), these generally give random results and are often difficult to implement in practice, for example in a hospital environment at the patient's bedside.

[0009] A problem is therefore to be able to provide a reliable assessment of the recruitability of a patient suffering from ARDS in order to be able to personalize their ventilation, in particular the PEEP setting to be applied to them, to ensure effective, non-harmful ventilation, in particular if the patient is non-recruitable.

[0010] One solution relates to a medical ventilator, i.e. a respiratory assistance device, comprising: - a gas circuit comprising an inspiratory branch for conveying a respiratory gas and an expiratory branch for evacuating the exhaled gas to the atmosphere, - flow rate measuring means configured to determine at least one gas flow rate in the gas circuit, - pressure measuring means configured to determine at least one gas pressure in the gas circuit, - a PEP valve arranged on the expiratory branch, - a graphic display, and - microprocessor control means cooperating with the flow measurement means, the pressure measurement means, the PEP valve and the graphic display.

[0011] Furthermore, according to the invention: - the control means are configured to:

[0012] a) determining an RI ratio from the flow rate and pressure measurements made by the flow rate measuring means and the pressure measuring means, where the RI ratio is such that:

[0013] RI ratio = Created / Crs

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[0024] Or : - Creates the compliance of the patient's recruited lungs and - Crs is the compliance of the respiratory system, b) order a display on the graphic display of the calculated RI ratio, - and the graphic display is configured to display the RI ratio. According to the invention, we call: - PEP: the residual gas pressure maintained by a medical ventilator above atmospheric pressure (i.e. 1 atm), in the ventilator's patient circuit, therefore indirectly also in the airways of a person, i.e. of a patient, at the end of expiration, i.e. at the end of each of its expiratory phases. - “RI ratio”: the recruitment / inflation ratio of a person’s lungs, typically a patient (for recruitment to inflation ratio in English) who estimates the capacity of an additional part of the lungs to be recruited, that is to say opened, to participate in gas exchange by implementing PEP. - patient: a person or human being (e.g. man, woman, etc.) whether an adult, an adolescent, a child, a baby, a newborn or other person suffering from a respiratory disorder or pathology, such as ARDS or other, requiring artificial ventilation. Depending on the embodiment considered, the medical ventilator of the invention may comprise one or more of the following features: - the control means are configured to determine the compliance (Crs) of the respiratory system (Crs) such that: Crs = Vte / (Ppiat - low PEP_measured) Or : • Pplat is the plateau pressure at PEPlow, where: PEPlow = PEPhigh- A with high PEP between 10 and 30 cmH20 and A between 5 and 15 cmH20, • Low PEEP_measured is a low PEEP value measured by the pressure sensor, and • Life is the tidal volume expired by the patient (at low PEEP). - the control means are configured to determine the compliance (Created) of the patient's recruited lungs such as: Created = AVrec / tPFP., - PFP. -1 v iw / high_measured A low_measured / where AVrec is the gas volume recruited with: AVrec = AEELVmesUré- AEELVestimated- Vte Or : • AEELVmeSuré is the gas volume AEELVmesUré measured and generated by the transition between PEPhaute and PEPbasse, and AFFT V - Ers (PFP- PFP u 1 / ti / i / a-, v estimate . y a a_,a high_measure x low_measure / *

[0025] - the control means are further configured to determine a recruitment state- patient stability by comparing the Rl-ratio determined for the patient considered with a given recruitability threshold value, e.g. prefixed, and determining that:

[0026] i) the patient is non-recruitable when the RI ratio is less than or equal to the recruitability threshold value, or

[0027] ii) the patient is a recruiter when the RI ratio is greater than the recruitment threshold value stability. the recruitability threshold value is adjustable, i.e. modifiable by the user. the recruitability threshold value is between 0 and 2. the recruitability threshold value is equal to 0.5. the control means are further configured to control a display on the graphic display of the patient's recruitability status. The graphical display is configured to display the patient's recruitability status. the control means are configured to determine the calculated RI ratio, after activation by the user of a selection means displayed on the graphic display, preferably by digitally pressing a virtual key or a numeric keypad. the control means are further configured to determine a recommendation for action to be taken based on the recruitability status having been determined and furthermore to command a display on the graphic display of the recommendation for action to be taken. The graphical display is configured to display the recommended action to be taken. it includes storage means configured to store recommendations for action to be taken including an increase in PEEP, a decrease in PEEP or a maintenance of PEEP. It further includes a micro-blower as a gas source supplying the inspiratory branch of the gas circuit with air or air / oxygen mixture. the control means include one (or more) microprocessor(s). the control means comprise (at least) an electronic card carrying the microprocessor(s). the microprocessor(s) implements one or more algorithms. It includes means of storage, such as computer memory. the storage means are arranged on the electronic card. It includes means of electrical supply. the means of electrical supply include an electrical cord and a mains connection plug (110 / 220 V) and / or a rechargeable battery(ies), and possibly a current transformer. the graphic display is a digital touch screen, i.e. a digital touch panel, i.e. one that can be controlled by the user pressing their fingers on the screen panel, to make choices, selections, entries, validations, launch actions, activate functionalities, etc. or carry out other actions. the display screen is of the color display type. the display screen is configured to display selection means, such as a numeric keypad or one or more digital selection keys. It includes a pressurized gas source to provide gas flow to the inspiratory limb. the source of pressurized gas is a motorized micro-blower, i.e. with an electric motor. the control means are configured to control the micro-blower. the control means are configured to control the operation of the micro-blower, in particular the accelerations or decelerations of the micro-blower. the power supply means supply electric current to the components requiring electric current to operate, such as the control means, the motorized micro-blower, the display screen or other elements.

[0028] The invention will now be better understood thanks to the following detailed description, given for illustrative but non-limiting purposes, with reference to the appended figures among which:

[0029] [Fig.l] schematizes an embodiment of the internal architecture of a medical ventilator according to the invention; and

[0030] [Fig.2] shows schematically an example of display on the display screen of a medical ventilator according to the invention.

[0031] [Fig.l] schematizes an embodiment of the internal architecture of a medical ventilator 1 according to the invention, that is to say a ventilatory assistance device, usable for treating a person, that is to say a patient, suffering from ARDS or other respiratory pathologies.

[0032] The ventilator 1 supplies the patient with a respiratory gas, such as an air / oxygen gas mixture, during each inspiratory phase of the patient and discharges exhaled gas from the patient's lungs during each expiratory phase.

[0033] The ventilator is connected to the patient via a gas circuit 2 which here has two branches comprising an inspiratory branch 2-1 and an expiratory branch 2-2, allowing the gas supplied by a gas source to be conveyed.

[0034] The inspiratory branch 2-1 and the expiratory branch 2-2 are connected fluidly- specifically to a junction piece 3, such as a Y-piece, allowing the junction to be made between the two branches 2-1, 2-2. The patient interface 10, such as a mask or an intubation probe, is fluidically connected to the junction piece 3.

[0035] The supply of oxygen (O2) is ensured by the inspiratory branch 2-1 and the elimination of carbon dioxide (CO2) exhaled by the patient is ensured by the expiratory branch 2-2, the terminal end of which leads to the atmosphere, via for example an outlet for exhaled gases 2-3 located at the level of the casing 11 of the ventilator 1.

[0036] The expiratory branch 2-2 also comprises a PEEP valve 12 arranged upstream of the expired gas outlet 2-3 used to adjust the PEEP level to ensure, according to the invention, effective ventilation of the patient and to avoid harmful ventilation if the patient is non-recruiting, as explained below.

[0037] The gas circuit 2 may comprise internal gas passages arranged in the outer casing or shell 11 of the ventilator 1 and flexible conduits connecting the ventilator 1 to the patient respiratory interface 10.

[0038] The gas flow is provided by a pressurized gas source 4, namely here a micro-blower 14, also called a turbine or compressor, sucking in ambient air via an air inlet 4-1 of the fan 1 opening into the atmosphere and furthermore supplied with gaseous oxygen via an oxygen inlet 4-2 of the fan 1 through which oxygen enters from an external oxygen source connected to the fan 1 by a flexible hose, such as a pressurized oxygen cylinder, or an oxygen distribution wall outlet supplied with oxygen by an oxygen delivery pipe connected to an oxygen storage, or even an oxygen concentrator.

[0039] Alternatively, the micro-blower 14 can be replaced by a control valve (not shown) for the gas supply arranged between the air inlet 4-1 of the ventilator 1 and the inspiratory branch 2-1, for example in place of the micro-blower 14 in [Fig.l]. In this case, the air inlet 4-1 of the ventilator 1 is supplied by a flexible conduit fluidically connected to a medical air distribution wall outlet carried by a wall of a hospital building and supplied with medical air by a medical air delivery pipe connected to a medical air storage or a medical air production installation, such as a PSA type installation, i.e. Pressure Swing Adsorption, making it possible to produce medical air on site, typically in a hospital building, such as a hospital, a clinic or the like.

[0040] In all cases, an air / oxygen mixture is obtained (O2 content >21% vol.) which is conveyed to the patient via the inspiratory branch 2-1 of the gas circuit 2 of the ventilator 1.

[0041] Furthermore, pressure measuring means (i.e. a device) 5, such as a pressure sensor, are provided, and flow measuring means (i.e. a device) 6, such as a mass flow sensor or a differential pressure sensor, are integrated in the fan 1 on the gas circuit 2 in order to determine a pressure and a flow rate of the gas, i.e. of the air / O2 mixture flow circulating therein.

[0042] More precisely, the pressure measuring means 5 are configured and arranged to determine at least one gas pressure, for example a pressure reflecting the pressure in the patient's airways, while the flow measuring (i.e. determining) means 6 determine at least one gas flow rate value corresponding to the gas flow rate in the gas circuit 2 ensuring the routing of the gas coming from the ventilator 1, i.e. typically in the inspiratory branch 2-1.

[0043] Means or a control unit 7 making it possible to operate in particular the data processing, such as measurements, and the various controls of the fan 1 are provided in the fan 1. They comprise at least one microprocessor 7-1, such as a microcontroller, implementing one or more algorithms, preferably carried by an electronic card 7-2.

[0044] Furthermore, the control means or unit 7 also serve to control the micro-blower 14 (or the control valve (not shown) of the gas supply ensuring the supply of gas from one or more wall outlets) in order to supply the gas during the patient's inspiratory phases and reduce or stop this supply during his expiratory phases.

[0045] Furthermore, according to the invention, the control means or unit 7 also control the PEP valve 12 which makes it possible to adjust the patient's PEP level during gas expirations.

[0046] The desired PEEP level is set by the user on the ventilator's HMI, i.e. the nursing staff, as explained below. In general, the PEEP is between 0 and 30 cmH20, or sometimes even higher, depending on the category of patient to be treated, i.e. adult, adolescent, child, newborn or other.

[0047] The pressure measuring means 5 and the flow measuring means 6 cooperate with the control means 7. More precisely, the pressure measuring means 5 and flow measuring means 6 provide the pressure and flow measurements that they carry out, to the control means 7, which then carry out a processing of these data, that is to say of the measurements received, in particular to determine the volumes generated by the ventilator 1, that is to say delivered by the gas source 4, for example the inspired volume and the expired volume, from the successive gas flow measurements.

[0048] The pressure and flow measurements may be measured values ​​or signals corresponding to values ​​measured by the sensors.

[0049] The fan 1 also comprises a graphic display or display screen 8 for displaying data, information, curves or other graphic representations, alarms, settings, selections, menus, icons or the like. The display on the display screen 8 is controlled by the control means 7.

[0050] Furthermore, an electric current source 9, i.e. electric power supply means, is also provided to supply electric current to the various components of the fan 1 requiring electric current to operate, such as the control means 7, the display screen 8, the micro-blower 14, the sensors, etc.

[0051] The electric current source 9 may comprise one or more internal rechargeable batteries which may be associated with a current transformer, and / or means of connection to the mains (110 / 200 V), such as an electric cord provided with a connection plug or the like.

[0052] The display screen 8 is preferably a digital touch screen, i.e. a digital touch panel, i.e. one that can be controlled by digital presses by the user on the panel of the screen 8, to make choices, selections, entries, validations, launch actions, activate functionalities, etc. or perform other actions. Advantageously, the display screen 8 is of the color display type.

[0053] Preferably, the display screen 8 is configured to display selection means, such as a specific monitoring block, of the monitoring mode and / or the recruitment / inflation ratio or “RI ratio” (for recruitment to inflation ratio in English) according to the invention, as detailed below.

[0054] A digital, i.e. tactile, press by the user, i.e. healthcare personnel, such as a doctor, on this monitoring pad displayed on the screen panel 8 makes it possible to select this mode and therefore to activate the different stages of the automatic calculation of the RI ratio, which are given below.

[0055] In other words, the user's pressing on the specific monitoring pad of the RI ratio mode displayed on the screen panel 8 of the display screen 8 is recognized and transmitted to the control means 7 which then carry out appropriate data processing, in particular determining the actions to be carried out which include the calculation of the RI ratio and its subsequent display on the display screen 8.

[0056] The calculation of the RI ratio is then done automatically by the control means 7, as detailed below.

[0057] Generally speaking, the control means 7 with microprocessor 7-1 cooperate with the flow measurement means 6, the pressure measurement means 5, the PEP valve 12, the graphic display 8 and the source of pressurized gas 4, such as the micro- blower 14 or the gas supply control valve (not shown) used to control the air supply from a wall outlet for example.

[0058] Within the control means 7, the microprocessor 7-1 is configured to calculate the RI ratio in the following manner by controlling the different components of the fan 1 necessary for this calculation.

[0059] More precisely, we operate as follows:

[0060] a) modification or fixing, typically by a doctor, of the respiratory frequency (Fr) so that the control means 7, in particular the microprocessor 7-1, control the micro-blower to deliver the gas at a frequency of between 4 and 10 breaths per minute; however, according to another embodiment, the frequency can be modified automatically by the ventilator, and possibly validated by a doctor by pressing a validation key for example,

[0061] b) passage to or fixation, by control of the expiratory valve 12 by the control means 7, of a so-called “high” PEP or PEPhaute between 10 and 30 cmH20, preferably between 10 and 25 cmH20, for example 15 cmH20,

[0062] c) measurement by the pressure sensor 5 of a PEPhaute_meSurée,

[0063] d) reduction of the PEP of the expiratory valve 12 by the control means 7, up to a so-called “low” PEP or low PEP, such as:

[0064] PEPlow = PEPhigh - A

[0065] Where: - PEPhaute is between 10 and 30 cmH20, for example 15 cmH20, - A is a value between 5 and 15 cmH20, typically equal to approximately 10 cmH20

[0066] From there, we have for example PEPbasse = 5 cmH20 (for A = 10 cmH20 and PEPhaute=15 cmH20),

[0067] e) determination of the gas volume AEELVmesUré (End Expiratory Lung Volume or end-of-expiration lung volume) which is measured and generated by the transition between PEPhaute and PEPbasse, the gas volume being determined by the control means 7 by integration of the flow rate measured by the flow rate measuring means 6 during said transition.

[0068] f) measurement of the tidal gas volume (Vte) at low PEP, which is the tidal volume expired by the patient (Vte = tidal volume expired), determined by the control means 7 by integration of the expired flow measured by the flow measuring means 6 during the expiration time at low PEP.

[0069] g) setting an inspiratory pause time (tpi) of up to 0.6 sec, typically between approximately 0.1 and 0.4 sec,

[0070] h) measurement by the pressure sensor 5 of the plateau pressure Ppiat obtained at PEPbasse, that is to say the pressure at the end of inspiration at the instant when the flow rate measured by the

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[0084] flow measurement means 6 is zero, i) measurement by pressure sensor 5 of a low PEP_measured, j) calculation of the Crs compliance of the respiratory system at low PEP, where: Crs = Life / (Ppiat _ ppp ,) x bass_measured / k) estimation of the AEELV volume estimated by a reduction of the PEEP from PEPhaute to PEPbasse (eg between 15 and 5 cmH20) predicted by the compliance of the system at PEPbasse, namely Aesbmb Crs (PEP haute_mesurée - PEP basse_mesuréeX 1) calculation of the recruited gas volume Vrec where: AVrec = AEELVmeSuré-AEELVestimated- Vte m) calculation of the compliance of the recruited lungs Created such that: Create = AVrec / tPFP., - PFP. -1 vit / V v iw / high_measured A low_measured / n) calculation of the recruitment / inflation ratio or RI ratio, such as: RI ratio = Created / Crs Once the RI ratio has been calculated by the control means 7, the latter control its display on the display screen 8, as well as preferably information on the recruitability status of the patient, for example on one or more monitoring blocks 8-1, 8-2 displayed on the display screen 8 of the ventilator 1. Thus, [Fig.2] schematizes a display on the display screen 8, of a first monitoring block 8-1, that is to say a display window, making it possible to visualize the RI ratio calculated by the control means 7 and the recruitability status of the patient P. The recruitability status of patient P is determined by the control means 7 in the following manner from the RLratio: - if the RI ratio is less than or equal to a threshold value, for example 0.5, the control means 7 determine that the patient is a non-recruiter, - conversely, if the RI ratio is higher than the threshold value, the control means 7 determine that the patient is a recruiter. The threshold value is set by default on the ventilator 1, can be adjusted by the user, for example a doctor at the HMI level, and stored in a memory 14 of the ventilator 1 and / or in a microprocessor 7-1 of the control means 7. Advantageously, the threshold value is between 0 and 2, in particular depending on the doctor's decision, typically the threshold value is equal to 0.5, but of course, depending on the case, it could be greater than 0.5, for example equal to 0.6, 0.7, 0.8, 0.9 or 1, or even more. As already stated, the control means 7 can then command a display, i.e. visualization, on the display screen 8, of information relating to the recruitability status of the patient having been thus determined, typically a text signaling this recruitability status of the patient, for example “recruiting patient” or “non-recruiting patient”, as illustrated in [Fig. 2], and / or a graphic representation with a color code dedicated to each state, such as a green patient face for a recruiting patient and a red one for a non-recruiting patient, or any equivalent information allowing healthcare staff to immediately and / or easily distinguish a recruiting patient from a non-recruiting patient.

[0085] Advantageously, the control means 7 can also be configured to determine and control a display on the display screen 8 of a recommendation for action to be taken by the healthcare staff as a function of the recruitability status having been determined for a given patient, for example in a second monitoring block 8-1, as shown diagrammatically in [Fig.2], in particular: - for a non-recruiting patient, propose or recommend maintaining or reducing the set PEP value, or - for a recruiting patient, propose or recommend an increase in the PEEP value and / or a maximum PEEP threshold value not to be exceeded.

[0086] As illustrated in [Fig.2], the recommendation for action to be taken by the healthcare personnel which is displayed on the display screen 8 may be, for example, textual information of the type “maintain PEEP”, “increase PEEP” or “decrease PEEP”, or any similar or equivalent indication.

[0087] It may be accompanied by a display of a graphic representation allowing the nursing staff to better visualize the recommended action to be taken, such as an arrow pointing upwards to indicate an increase in positive pressure or, conversely, downwards to indicate a decrease in positive pressure, or even an “=” sign for maintaining or preserving the current positive pressure.

[0088] In addition, the control means 7 can also be configured to control a display on the display screen 8:

[0089] - of a graphical representation and / or the value of the RI ratio having been determined as a unitless value between 0 and 5, and / or

[0090] - of one (or more) real-time curve(s) (8-3) of pressure or volume type obtained at from several successive measurements of gas pressure and / or gas flow rate processed by the microprocessor of the control means 7, as illustrated in [Fig.2].

[0091] In addition, other information useful to the nursing staff can be displayed (8-4) on the display screen 8, such as the tidal volume (Vte), the respiratory rate (Fr), the expiratory pressure or PEEP, or other ventilatory parameters, as visible in [Fig.2].

[0092] A ventilator 1 according to the invention is of great help to the nursing staff because it provides them with a reliable assessment of the recruitability of a patient suffering from ARDS, thanks to the calculation and display of the recruitment / inflation ratio or RI ratio, thus enabling them to personalize the ventilation of the patient in question, in particular the PEEP setting to be applied to them, to ensure effective, non-harmful ventilation, whether the patient is a recruiter or not.

[0093] Generally speaking, a medical ventilator 1 of the invention can be used to ventilate a person, i.e. a patient, suffering from respiratory distress, i.e. ARDS, by providing the healthcare personnel with an indication(s) of whether or not the lungs of the patient in question can be recruited and preferably also a recommendation for action to be taken regarding the PEP to be implemented.

[0094] Such information makes it possible to help the healthcare personnel, i.e. doctor or the like, to adapt the PEP setting, preferably in association with other available clinical data or parameters, such as real-time pressure, volume and / or flow rate curves or others.

[0095] Furthermore, such a ventilator has the advantage of making it possible to give an indication of the possibility of a patient's lungs opening further to participate in gas exchanges when implementing PEP on expiration, directly at the patient's bedside and without the need for additional equipment.

Claims

Claims

1. A medical ventilator (1) comprising: - a gas circuit (2) comprising an inspiratory branch (2-1) for conveying a respiratory gas and an expiratory branch (2-2) for evacuating the exhaled gas to the atmosphere, - flow rate measuring means (6) configured to determine at least one gas flow rate in the gas circuit (2), - pressure measuring means (5) configured to determine at least one gas pressure in the gas circuit (2), - a PEP valve (12) arranged on the expiratory branch (2-2), - a graphic display (8), and - control means (7) with microprocessor (7-1) cooperating with the flow measurement means (6), the pressure measurement means (5), the PEP valve (12) and the graphic display (8), characterized in that: - the control means (7) are configured to: a) determining an RI ratio from the flow and pressure measurements made by the flow measuring means (6) and the pressure measuring means (5), where the RI ratio is such that: RI ratio = Created / Crs Or : - Creates the compliance of the patient's recruited lungs and - Crs is the compliance of the respiratory system, b) order a display on the graphic display (8) of the calculated RI ratio, - and the graphic display (8) is configured to display (8-1) the RI ratio.

2. Ventilator according to claim 1, characterized in that the control means (7) are configured to determine the compliance (Crs) of the respiratory system (Crs) such that: Crs = Life / (Ppiat- low_measured PEEP), where: - Ppiat is the plateau pressure at low_PEEP, with: low_PEEP = high_PEEP - A and high_PEEP between 10 and 30 cmH20 and A between 5 and 15 cmH20, - low_measured PEEP is a low_PEEP value measured by the pressure sensor (5), and - Life is the tidal volume expired by the patient.

3. Ventilator according to claim 2, characterized in that the control means (7) are configured to determine the compliance (Created) of the recruited lungs of the patient such that: Created = AVrec / PFP., - PFP. - 1 v iw / ± high_measured A low_measured / where: AVrec is the recruited gas volume with: AVrec = AEELVmeSuré-AEELVeStimé- Vte where: - AEELVmeSuréis the gas volume AEELVmesUré measured and generated by the transition between PEPhaute and PEPbasse, and - AFFT V - Crs (PFP- PFP u 1 / ti / i yi— / v estimate . y a j_ / a high_measured x low_measured / *

4. Ventilator according to one of the preceding claims, characterized in that the control means (7) are further configured to determine a recruitability status of the patient by comparing the Rl-ratio determined for the patient in question with a given recruitability threshold value and by determining that: - the patient is non-recruitable when the RI ratio is less than or equal to the recruitability threshold value, or - the patient is recruitable when the RI ratio is greater than the recruitability threshold value.

5. Fan according to claim 4, characterized in that the recruitability threshold value is between 0 and 2, preferably equal to 0.

5.

6. Ventilator according to claim 1, characterized in that: - the control means (7) are further configured to control a display on the graphic display (8), of the recruitability status of the patient (8-1) and - the graphic display (8) is configured to display (8-1) the recruitability status of the patient.

7. Fan according to claim 1, characterized in that the control means (7) are configured to determine the calculated RI ratio, after activation by the user of a selection means (13) displayed on the graphic display (8), preferably by digitally pressing a virtual key or a numeric keypad.

8. Fan according to claim 1, characterized in that: - the control means (7) are further configured to determine a recommendation for action to be taken as a function of the recruitability status having been determined and further control a display (8-2) on the graphic display (8), of the recommendation for action to be taken, and - the graphic display (8) is configured to display the recommendation for action to be taken (8-2).

9. Ventilator according to claim 8, characterized in that it comprises storage means (14) configured to store recommendations for action to be taken including an increase in PEP, a decrease in PEP or a maintenance of PEP.

10. Ventilator according to claim 1, characterized in that it further comprises a micro-blower (14) as a gas source (4) supplying the inspiratory branch (2-1) of the gas circuit (2) with air or air / oxygen mixture.

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