Oxygen boost during mechanical ventilation of a patient

Abstract

A ventilator delivers breathing gas to a patient via a patient circuit connecting the ventilator and the patient. The ventilator is configured to, upon activation of an oxygen boost function of the ventilator, increase the oxygen concentration of the breathing gas so as to deliver oxygen-enriched breathing gas to the patient. The ventilator includes a control unit configured to determine the volume of a part of the patient circuit conveying breathing gas from the ventilator to the patient, determine a delay in delivery of the oxygen-enriched breathing gas to the patient based on the volume, and cause indication of the delay to an operator of the ventilator.

Claims

1. A ventilator for delivering a breathing gas to a patient, comprising: a control unit, wherein the breathing gas is delivered via a patient circuit, the patient circuit connecting the ventilator and the patient, the ventilator being configured to, upon activation of an oxygen boost function of the ventilator, increase an oxygen concentration of the breathing gas so as to deliver the oxygen-enriched breathing gas to the patient, and wherein the control unit is configured to (a) determine a volume of a part of the patient circuit conveying the breathing gas from the ventilator to the patient, (b) determine a delay in delivery of the oxygen-enriched breathing gas to the patient based on the volume, and (c) cause an indication of the delay to an operator of the ventilator, and (d) calculate, based on the delay, a start point in time at which the oxygen-enriched breathing gas reaches the patient and (e) cause an indication of the start point in time to the operator of the ventilator.

2. The ventilator according to claim 1, wherein the ventilator, upon activation of the oxygen boost function, is configured to deliver the oxygen-enriched breathing gas during a set period of time, the control unit being configured to (a) calculate, based on the delay and the set period of time, a finish point in time at which the oxygen-enriched breathing gas has been delivered to the patient for the set period of time and (b) cause an indication of the finish point in time to the operator of the ventilator.

3. The ventilator according to claim 2, wherein the control unit is configured to cause an indication of the time remaining until the finish point in time.

4. The ventilator according to claim 1, wherein the control unit is configured to cause an indication of a wash-in-wash-out process of oxygen content in the breathing gas reaching the patient, caused by the activation of the oxygen boost function.

5. The ventilator according to claim 1, further comprising: a display unit connected to the control unit, wherein the control unit is configured to cause the indication by causing display of an indicator on of the display unit.

6. The ventilator according to claim 1, wherein the control unit is configured to cause the indication by causing display of an indicator on a display unit of a monitoring system to which the ventilator is connected.

7. The ventilator according to claim 1, wherein the indicator is a dynamic indicator indicating whether the breathing gas currently reaching the patient is the oxygen-enriched breathing gas or not.

8. The ventilator according to claim 7, wherein the indicator indicates one of at least two colours, a first colour of the at last two colours representing a first state in which the oxygen-enriched breathing gas is delivered to the patient, a second colour of the at least two colours representing a second state in which the non-oxygen-enriched breathing gas is delivered to the patient, the indicator indicating one of the at least two colours in dependence of whether the breathing gas currently reaching the patient is the oxygen-enriched breathing gas or the non-oxygen-enriched breathing.

9. The ventilator according to claim 1, wherein the ventilator, upon the activation of the oxygen boost function, is configured to increase the oxygen concentration of the breathing gas to a set level of the oxygen concentration, the oxygen-enriched breathing gas being the breathing gas having the set level of oxygen concentration.

10. The ventilator according to claim 1, wherein the control unit is configured to automatically determine the volume of the part of the patient circuit based on information related to pressure changes in response to changes in a gas volume in the patient circuit.

11. The ventilator according to claim 1, wherein the control unit is configured to determine the volume of the part of the patient circuit during a pre-use check of the ventilator, prior to connection of the patient to the ventilator, during prevention of a gas flow through a proximal and expiratory part of the patient circuit.

12. The ventilator according to claim 1, wherein the control unit is configured to (a) automatically determine if a humidifier is present in a part of the patient circuit conveying the breathing gas from the ventilator to the patient and (b) determine a volume of the part of the patient circuit based on the presence of the humidifier.

13. A method for providing an improved oxygen boost functionality of a ventilator delivering breathing gas to a patient via a patient circuit, the patient circuit connecting the ventilator and the patient, the ventilator being configured to, upon an activation of an oxygen boost function of the ventilator, increase an oxygen concentration of the breathing gas so as to generate oxygen-enriched breathing gas to be delivered to the patient, the method comprising the steps of: determining a volume of a part of the patient circuit conveying the breathing gas from the ventilator to the patient; determining a delay in delivery of the oxygen-enriched breathing gas to the patient based on the volume, and causing an indication of the delay to an operator of the ventilator, andcalculating, based on the delay, a start point in time at which the oxygen-enriched breathing gas reaches the patient, andcausing an indication of the start point in time to the operator of the ventilator.

14. A computer program for providing an improved oxygen boost functionality of a ventilator delivering breathing gas to a patient via a patient circuit, the patient circuit connecting the ventilator and the patient, the ventilator being configured to, upon an activation of an oxygen boost function of the ventilator, increase an oxygen concentration of the breathing gas so as to generate the oxygen-enriched breathing gas to be delivered to the patient, the computer program comprising computer-readable program code which, when executed, causes a control unit of the ventilator to perform steps of claim 13.

15. A ventilator for an automatic determination of a presence of a humidifier in an inspiratory line of a patient circuit, the ventilator being connected the patient circuit, the ventilator comprising: a control unit configured to: cause a change in a gas composition in the patient circuit through a supply into the inspiratory line of a gas having a different composition than another gas previously occupying the patient circuit; determine a rate of change in the gas composition downstream a part of the inspiratory line, and determine if the humidifier is present in the part of the inspiratory line based on the rate of change in the gas composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description provided hereinafter and the accompanying drawings which are given by way of illustration only. In the different drawings, same reference numerals correspond to the same element.

(2) FIG. 1A illustrates a ventilator according to an exemplary embodiment of the present disclosure, connected to a patient circuit through which the ventilator is connected to a patient.

(3) FIG. 1B illustrates the ventilator in FIG. 1A prior to connection to the patient.

(4) FIG. 1C illustrates the ventilator in FIGS. 1A and 1B connected to another patient circuit comprising a humidifier in an inspiratory line thereof, prior to connection to the patient.

(5) FIG. 2A illustrates a graph representing measured oxygen concentration over time upon delivery of oxygen into an inspiratory line of an air-containing patient circuit, measured downstream a part of the inspiratory line not comprising any humidifier.

(6) FIG. 2B illustrates a graph representing measured oxygen concentration over time upon delivery of oxygen into an inspiratory line of an air-containing patient circuit, measured downstream a part of the inspiratory line comprising a humidifier.

(7) FIGS. 3A and 3B illustrate an exemplary GUI of a ventilator according to an exemplary embodiment of the present disclosure, which GUI is configured to indicate a delay in delivery of oxygen-enriched breathing gas from the ventilator to the patient upon activation of the oxygen boost function of the ventilator.

(8) FIG. 4 illustrates an exemplary embodiment of a method for providing improved oxygen boost functionality of a ventilator according to the principles of the present disclosure.

DETAILED DESCRIPTION

(9) FIG. 1A illustrates a ventilator 1 according to an exemplary embodiment of the present disclosure. In FIG. 1A, the ventilator 1 is connected to a patient 3 via a patient circuit 5 and configured to deliver breaths of pressurized breathing gas to the patient 3. The patient circuit 5 typically comprises a conventional ventilator breathing system (VBS).

(10) The ventilator 1 is configured for delivery of oxygen and at least one further gas or gas mixture to the patient 3. In this exemplary embodiment, the ventilator 1 is connected to two gas sources 7A and 7B, such as wall outlets for the supply of pressurized gas often available in medical care facilities (medical pipeline system), compressors or gas tanks. A first gas source 7A is a gas source for the supply of oxygen and a second gas source 7B is a gas source for the supply of air.

(11) The ventilator 1 comprises a gas mixing module 9 for regulating the composition of the breathing gas to be delivered to the patient 3. The breathing gas composition may be any of at least air (approximately 21% oxygen), oxygen-enriched air (>21% oxygen) and pure oxygen (100% oxygen).

(12) The ventilator 1 further comprises an inspiratory valve 11 for regulating the pressure and/or flow of breathing gas delivered to the patient 3, and an expiratory valve 13 for regulating an expiratory pressure applied to the patient 3 during expiration.

(13) Yet further, the ventilator 1 comprises a control unit 15 for controlling the gas mixing module 9, the inspiratory valve 11 and the expiratory valve 13 based on ventilator settings and sensor data obtained by various sensors of the ventilator.

(14) The patient circuit 5 comprises an inspiratory line for conveying breathing gas from the ventilator 1 to the airways of the patient 3. The inspiratory line comprises an inspiratory length of tubing 17 connecting an inspiratory port (outlet) 19 of the ventilator with an inspiratory port (inlet) 21 of a Y-piece 23, and a part of said Y-piece 23 connecting said inspiratory port 21 with a patient-connection port 25 of the Y-piece, which patient-connection port 25 is connected to a patient connector 27 connecting the patient circuit 5 to the airways of the patient 3. In this exemplary embodiment, the patient connector 27 is a breathing mask. In other embodiments, the patient connector may be a tracheal tube, nasal prongs or any other type of patient connector known in the art. The patient circuit 5 further comprises an expiratory line for conveying expiration gas exhaled by the patient 3 to the ventilator 1. The expiratory line comprises an expiratory length of tubing 18 connecting an expiratory port (outlet) 22 of said Y-piece 23 with an expiratory port (inlet) 33 of the ventilator, and a part of the Y-piece 23 connecting said expiratory port 22 of the Y-piece with the patient-connection port 25 of the Y-piece

(15) The ventilator 1 is provided with oxygen boost functionality, meaning that it is configured to temporarily increase the oxygen concentration of the breathing gas delivered to the patient 3 upon activation of an oxygen boost function. In this exemplary embodiment, the ventilator is configured to, upon activation of the oxygen boost function, temporarily increase the oxygen concentration from a baseline level used prior to activation of the oxygen boost function to a desired and increased level of oxygen concentration (herein referred to as the oxygen boost level) and, when a certain time period has elapsed since activation of the oxygen boost function (herein referred to as the oxygen boost duration), return to the baseline level of oxygen concentration. The oxygen boost level is a set level of oxygen concentration which may be predefined (e.g. to 100% oxygen) or selectable by an operator of the ventilator 1.

(16) In some embodiments, the ventilator 1 may be configured to automatically activate the oxygen boost function upon detection of a situation in which certain criteria indicating an increased demand for oxygen by the patient 3 is met, e.g. when at least one sensor-monitored parameter indicative of increased demand for oxygen by the patient 3 exceeds a predetermined threshold value.

(17) Typically, however, the oxygen boost function is activated manually by an operator of the ventilator 1, e.g. by pressing a button causing the oxygen boost function of the ventilator 1 to be activated, such as a touch-button displayed on a touch-sensitive screen of a display unit 29 of the ventilator.

(18) In accordance with the principles of the present disclosure, the ventilator 1 is configured to determine a delay in delivery of the oxygen-enriched gas from the ventilator 1 to the patient 3, based on the volume of the inspiratory line of the patient circuit 5, and to communicate said delay to the operator of the ventilator. The delay is a time period between activation of the oxygen boost function, i.e. the point in time at which the ventilator 1 starts to deliver oxygen-enriched gas (breathing gas having increased oxygen concentration compared to the baseline level of oxygen concentration) to the point in time at which oxygen-enriched breathing gas reaches the patient. In this embodiment in which the ventilator 1 starts to deliver breathing gas having an oxygen concentration corresponding to the oxygen boost level immediately upon activation of the oxygen boost function, the delay may be defined as the time period between activation of the oxygen boost function and reception of the oxygen boost level by the patient 3.

(19) During start-up of the ventilator 1, prior to connection of the patient 3 to the ventilator, the ventilator 5 is configured to perform a pre-use check which may include tests and measurements of internal technical functionality, internal leakage, pressure sensors, flow sensors, gas meters (e.g. oxygen sensors), etc.

(20) The ventilator 1 is configured to determine the volume of the inspiratory line of the patient circuit 5 during said pre-use check, and to use the thus determined inspiratory line volume in the determination of the above mentioned delay, so as to be able to communicate it to the operator of the ventilator, e.g. by communicating the point in time at which the patient 3 starts to receive the oxygen-enriched breathing gas, and/or the point in time at which the patient 3 has received oxygen-enriched breathing gas for a period of time corresponding to the oxygen boost duration.

(21) The control unit 15 of the ventilator 1 is configured to automatically determine the volume of the inspiratory line of the patient circuit 5 through execution of a computer program, stored in a digital memory (not shown) of the ventilator, and executed by a processor (not shown) of the ventilator. The memory and the processor may be comprised in the control unit 15. The computer program may be a software module forming part of a pre-use check software which is automatically executed upon start-up of the ventilator for conducting said pre-use check of the ventilator 1.

(22) The volume of the inspiratory line is typically determined by the control unit 15 based on information related to pressure changes in the patient circuit 5 in response to changes in gas volume in the patient circuit, i.e. a pressure-to-volume response of the patient circuit 5.

(23) FIG. 1B illustrates the ventilator 1 and the patient circuit 5 during execution of the pre-use check of the ventilator 1, prior to connection the patient, at the time of determination of the volume of the inspiratory line of the patient circuit 5.

(24) First, the control unit 15 causes an occlusion instruction to be displayed on the display unit 29, instructing the operator of the ventilator 1 to occlude the proximal part of the patient circuit 5, e.g. by manually occluding the Y-piece or the proximal end of any patient connector already connected to the patient-connection port 25 of the Y-piece 23. This may be achieved by the operator by simply pressing a hand 31 against the proximal part of the patient circuit 5 to make a sealing engagement against the opening thereof. Also, the control unit 15 closes the expiratory valve 13 of the ventilator 1 to prevent any gas introduced into the patient circuit via the inspiratory valve 11 from leaving the patient circuit 5 via the expiratory part thereof.

(25) Then the control unit 15 opens the inspiratory valve 11 to deliver a flow of gas into the patient circuit 5. Typically, the gas used during determination of the volume of the inspiratory line is air. The control unit 15 determines the volume of gas that is introduced into the patient circuit 5, typically from flow measurements obtained by a flow sensor (not shown) located in an inspiratory module of the ventilator 1, between the inspiratory valve 11 and the inspiratory port 19. The control unit 15 is further configured to receive pressure measurements related to the pressure in the patient circuit 5 from at least one pressure sensor (not shown), e.g. a pressure sensor disposed in the Y-piece 23 of the patient circuit 5 or in an expiratory module of the ventilator 1, between the expiratory port 33 of the ventilator and the expiratory valve 13.

(26) The control unit 15 then derives the volume of the patient circuit 5 based on the pressure-to-volume response of the patient circuit, i.e. based on the volume of delivered gas required to cause a certain change in pressure in the patient circuit 5. More precisely, the control unit 15 calculates a compliance value, C.sub.tot, as:
C.sub.tot=V/P,eq. (1)

(27) where V is the change in gas volume in the patient circuit 5 (i.e. the volume of gas delivered through the inspiratory valve 11), and P is the pressure change in the patient circuit caused by said change in gas volume. The thus derived compliance value, C.sub.tot, is the sum of the compliance of the tubing of the patient circuit 5 (C.sub.pc) and the compliance of the gas (air) that was present in the patient circuit 5 prior to said change in gas volume (C.sub.gas), meaning that:
C.sub.tot=C.sub.pc+C.sub.gaseq. (2)

(28) The compliance of the gas that was present in the patient circuit 5 prior to said change in gas volume equals the volume of said gas divided by the ambient pressure, i.e.:
C.sub.gas=V.sub.gas/P.sub.amb,eq. (3)

(29) where V.sub.gas is the volume of the gas (air) that was present in the patient circuit 5 prior to the opening of the inspiratory valve 11, and P.sub.amb is the ambient pressure, i.e. the pressure surrounding said gas. The volume of the gas (air) that was present in the patient circuit 5 prior to the opening of the inspiratory valve 11 equals the volume of the patient circuit, i.e.:
V.sub.gas=V.sub.pc,eq. (4)

(30) where V.sub.pc is the unknown volume of the patient circuit. Combining equations 1-4 yields:
V.sub.pc=((V/P)C.sub.pc)*P.sub.ambeq. (5)

(31) Thus, assuming that the compliance of the patient circuit tubing (C.sub.pc) is zero or nearly zero, i.e. that the patient circuit material is stiff, the unknown volume of the patient circuit, V.sub.pc, can be derived as the quotient V/P multiplied by ambient pressure. The ambient pressure may be measured by a sensor that is communicatively connected to the control unit 15, or be assumed by the control unit 15 to be 1 atm (101,325 kPa).

(32) Based on the volume of the patient circuit 5, the control unit 15 may determine the volume of the inspiratory line conveying breathing gas from the ventilator 1 to the patient 3. For example, the control unit may be configured to assume that the volume of the inspiratory line constitutes 50% of the total volume of the patient circuit, meaning that the control unit is configured to determine the volume of the inspiratory line as:
V.sub.insp=0.5*V.sub.pc,eq. (6)

(33) where V.sub.insp is the volume of the inspiratory line. This is normally a good approximation as the volume of the inspiratory line typically constitutes half or approximately half the total volume of the patient circuit.

(34) However, if a humidifier for humidifying the breathing gas that is to be delivered to the patient is mounted in the inspiratory line, the volume of the inspiratory line (including the volume of the humidifier) typically constitutes substantially more than half the total volume of the patient circuit.

(35) FIG. 1C illustrates a ventilator set up wherein the inspiratory line of the patient circuit 5 comprises a humidifier 35.

(36) In cases where the inspiratory line comprises a humidifier, the control unit 15 of the ventilator may be configured to determine the volume of the inspiratory line (including the humidifier) taking both the calculated total volume of the patient circuit, V.sub.pc, and the presence of the humidifier into account. This means that the control unit 15, in case of the presence of a humidifier in the inspiratory line of the patient circuit 5, may be programmed to assume that the volume of the inspiratory line of the patient circuit constitutes a major part of the total volume of the patient circuit, i.e. that the volume of the inspiratory line constitutes more than 50% of the total volume of the patient circuit. In one embodiment, the control unit 15 is configured to determine the volume of the inspiratory line as 55%-65% of the calculated total volume of the patient circuit if a humidifier is present.

(37) The control unit 15 may be configured to receive information indicative of the presence of any humidifier from the operator of the ventilator 1, and use this information in the determination of the volume of the inspiratory line.

(38) However, the control unit 15 may also be configured to automatically determine if a humidifier is present in the inspiratory line. Preferably, the automatic determination of the presence of any humidifier in the patient circuit is also conducted by the control unit 15 during the pre-use check of the ventilator 1, and during occlusion of the proximal part of the patient circuit 5.

(39) Automatic determination of whether a humidifier is present in the inspiratory line of the patient circuit 5 may be made based on a measured rate of change in gas composition, caused by introduction through the inspiratory line of the patient circuit of a gas having a different composition than another gas currently occupying the patient circuit, measured downstream a part of the patient circuit in which a humidifier may be present.

(40) To this end, the control unit 15 is configured to cause a change in composition of the gas within the patient circuit 5 through introduction into the inspiratory line of the patient circuit 5 of a gas being different than a gas currently present in the patient circuit, and to determine if a humidifier is present in in a part of the inspiratory line by determining the rate of change in gas composition downstream said part of the inspiratory line, e.g. from gas composition measurements obtained by a gas sensor located in the Y-piece 23 or in an expiratory module of the ventilator 1.

(41) In one embodiment, the above described volume determination is made using air, meaning that the pressure-to-volume response of the patient circuit is determined during the supply of air into the inspiratory line of the patient circuit 5. When, during the pre-use check of the ventilator 1, the determination of the volume of the patient circuit (V.sub.pc) is made, the control unit 15 opens the expiratory valve 13 of the ventilator, still during occlusion of the proximal part of the patient circuit 5, and causes the ventilator 1 to switch from delivery of air to delivery of oxygen. A gas meter in form of an oxygen sensor (not shown), located downstream the part of the patient circuit 5 in which the humidifier 35 is located, measures the oxygen concentration of gas downstream said part of the patient circuit 5 and communicates the result of said measurements to the control unit 15 of the ventilator 1. The oxygen sensor may be located in the Y-piece 23 or the expiratory line of the patient circuit 5, or in an expiratory module of the ventilator 1. The control unit 15 is configured to determine the rate of change in oxygen concentration of the gas measured upon, based on the received measurement values. In one embodiment this is achieved by determining the time elapsed from the start of oxygen delivery by the ventilator 1 to the point in time at which the measured oxygen concentration reaches 90%, i.e. the time it takes to cause an increase in oxygen concentration from 21% (air) to 90%.

(42) FIGS. 2A and 2B illustrate the difference in measured oxygen concentration over time between a situation in which measurements are obtained downstream a part of the inspiratory line not comprising any humidifier (FIG. 2A) and a situation in which measurements are obtained downstream a part of the inspiratory line comprising a humidifier (FIG. 2B).

(43) FIG. 2A illustrates measured oxygen concentration in the absence of any humidifier. The left-hand graph shows the oxygen concentration (O.sub.2) of gas delivered by the ventilator 1 into the inspiratory line of the patient circuit 5, prior to and after said change from delivery of air to delivery of oxygen. The delivered oxygen concentration is seen to increase almost momentarily from a first level of oxygen concentration in air (21%) to a second level of oxygen concentration (100%) in pure oxygen. The right-hand graph shows the oxygen concentration of gas downstream the part of the patient circuit 5 in which a humidifier might be present, e.g. as measured by an oxygen sensor in the expiratory module of the ventilator 1. The measured response to the change in oxygen concentration is seen to be fairly quick. Based on the time elapsed from the start of oxygen delivery by the ventilator 1 to the point in time at which the measured oxygen concentration reaches 90%, the control unit may calculate the slope of the graph (k60), representing the mean rate of change in oxygen concentration from 21% to 90% of the gas measured upon.

(44) FIG. 2B illustrates measured oxygen concentration in the presence of a humidifier in the inspiratory line of the patient circuit 5. Here, the response to the change in oxygen concentration is seen to be considerably slower due to the increased degree of mixing of air and oxygen caused by the presence of the humidifier. Here, the mean rate of change in oxygen concentration from 21% to 90% yields a slope coefficient around 30.

(45) The control unit 15 may for example be programmed to assume that a humidifier is present in the inspiratory line of the patient circuit 5 if said slope coefficient falls below a predetermined threshold value.

(46) It should thus be appreciated that the control unit 15 may be configured to determine if a humidifier is present in a part of the inspiratory line of the patient circuit 5 by comparing the rate of change in gas composition (in this exemplary case oxygen concentration) downstream said part of the inspiratory line with a predetermined threshold value. The rate of change may, in this context, be represented by the above discussed slope coefficient, the time required to cause the increase in oxygen concentration from 21% to 90% or any other parameter indicative of said rate of change.

(47) Preferably, the control unit 15 is configured to determine if a humidifier is present in the inspiratory line of the patient circuit 5 not only based on the rate of change in measured oxygen concentration but also based on the determined (total) volume of the patient circuit. If this volume is bigger than the volume of a normal patient circuit, this too is an indication that a humidifier is present in the inspiratory line thereof. Therefore, the control unit is advantageously configured to establish if the determined volume of the patient circuit is bigger than the volume of a normal patient circuit, as described in the following.

(48) During supply of oxygen by the ventilator 1 (i.e. after having switched from delivery of air to delivery of oxygen during the pre-use check), the control unit 15 is configured to receive measurements on gas pressure and gas flow, and to determine the resistance and the type of the patient circuit 5 based on said pressure and flow measurements. Flow measurements may for example be provided to the control unit 15 by means of the above mentioned flow sensor in the inspiratory module of the ventilator 1, and pressure measurements may be provided by the above mentioned pressure sensor in the Y-piece 23 of the patient circuit 5 or the expiratory module of the ventilator 1.

(49) The control unit 15 is preferably configured to first cause delivery of a flow of oxygen of 10 lpm, and to calculate the resistance of the patient circuit based on the thus obtained pressure and flow values. If the resistance is high, meaning that it exceeds a predetermined threshold value, the control unit 15 is programmed to conclude that the patient circuit 5 is a neonatal type of patient circuit 5, whereby no further resistance measurements are performed and the resistance value already derived is used to compensate for resistive losses of the patient circuit 5 during subsequent ventilation of the (neonatal) patient. If, on the other hand, the resistance is low or relatively low (below said threshold value), the control unit 15 is configured to conclude that the patient circuit 5 is an adult type of patient circuit, and to cause delivery of an increased flow of oxygen through the patient circuit 5, e.g. a flow of 60 lpm. Based on the pressure values obtained at the increased flow level, the control unit 5 calculates a new resistance value which is used by the control unit 15 during subsequent ventilation of the (adult) patient 3 to compensate for resistive losses of the patient circuit 5.

(50) The measurement of the patient circuit resistance thus serves the double purposes of determining the type of the patient circuit and the resistive losses of the patient circuit.

(51) Once the type of the patient circuit 5 has been determined, the control unit 15 can determine whether the determined volume of the patient circuit is bigger than normal. To this end, the ventilator may store, e.g. in a digital memory thereof, a plurality of reference values indicative of typical volumes of patient circuits of different types, e.g. one reference value indicative of the volume of a typical neonatal patient circuit and one reference value indicative of the volume of a typical adult patient circuit. The control unit 15 may then compare the determined volume of the patient circuit 5 with the relevant reference value in dependence of the determined type of patient circuit, and determine whether or not the determined volume of the patient circuit is bigger than normal based on said comparison.

(52) If the response to the change in oxygen concentration is quick and the determined volume of the patient circuit (V.sub.pc) is not bigger than normal, then the control unit 15 is programmed to conclude that no humidifier is present in the inspiratory line of the patient circuit 5. If, however, the response to the change in oxygen concentration is slow and the determined volume of the patient circuit (V.sub.pc) is bigger than normal, then the control unit 15 is programmed to conclude that a humidifier is present in the inspiratory line of the patient circuit 5.

(53) Once the control unit 15 has determined whether the inspiratory line of the patient circuit 5 comprises a humidifier or not, the volume of the inspiratory line (V.sub.insp) may be determined based on the total volume of the patient circuit (V.sub.pc) and the presence of any humidifier. For example, as described above, the volume of the inspiratory line may be determined by the control unit as 50% of the total volume of the patient circuit in case of absence of any humidifier, and as 55%-65% of the total volume of the patient circuit in case of presence of a humidifier.

(54) In one embodiment, the control unit 15 may be configured to, if a humidifier is deemed to be present, determine the volume of the inspiratory line more precisely from the total volume of the patient circuit and the type of the humidifier.

(55) Typically, there is one type of humidifiers used for adult patient circuits (hereinafter referred to as adult humidifiers) and one type of humidifiers used for neonatal/pediatric patient circuits (hereinafter referred to as neonatal humidifiers). Before use, the humidifier is partly filled with water such that breathing gas passing through the humidifier is humidified before being delivered to the patient. The volume of the humidifier not filled by water adds volume to the inspiratory line of the patient circuit. This volume is typically 300 ml for an adult humidifier and 200 ml for a neonatal humidifier.

(56) The control unit 15 may be configured to determine the type of the humidifier based on the type of the patient circuit currently connected to the ventilator 1, determined in accordance with the above described principles. If the patient circuit is determined to be an adult patient circuit, then the humidifier is assumed to be an adult humidifier. If, on the other hand, the patient circuit is determined to be a neonatal/pediatric patient circuit, then the humidifier is assumed to be a neonatal humidifier.

(57) For example, the control unit 15 may be configured to determine the inspiratory line volume as 55%-60% of the total volume of the patient circuit if the humidifier is assumed to be a neonatal humidifier, and as 60%-65% of the total volume of the patient circuit if the humidifier is assumed to be an adult humidifier.

(58) The control unit 15 may also be configured to determine the volume of the inspiratory line of the patient circuit based on the total volume of the patient circuit and the volume of the humidifier itself. To this end, the control unit 15 may for example be configured to store a look-up table of typical humidifier volumes associated with different types of humidifiers, e.g. 300 ml for adult humidifiers and 200 ml for neonatal humidifiers, and to use these humidifier volumes in the determination of the inspiratory line volume. The control unit 15 may select the humidifier volume associated with the determined type of humidifier, and calculate the volume of the inspiratory line based on the so selected humidifier volume and the total volume of the patient circuit. In one exemplary embodiment, the control unit 15 is configured to calculate the volume of the inspiratory line of the patient circuit using the following relationship:
V.sub.insp=(V.sub.pcV.sub.h)/2+V.sub.h,(eq. 7)

(59) where V.sub.insp is the volume of the inspiratory line of the patient circuit, V.sub.pc is the total volume of the patient circuit, and V.sub.h is the active volume of the humidifier conveying breathing gas from the ventilator towards the patient, typically corresponding to the humidifier volume not filled by water. The determined volume of the inspiratory line may then be stored in a digital memory of the ventilator 1 for subsequent use during ventilation of the patient 3, and in particular upon activation of the oxygen boost function of the ventilator 1.

(60) When, during ventilation of the patient 3, the operator activates the oxygen boost function, the control unit 15 retrieves the volume of the inspiratory line from memory and uses it together with current ventilation settings in order to determine the delay in delivery of the oxygen-enriched gas to the patient 3. Said current ventilation settings typically includes the current minute ventilation of the patient 3, which may be a set parameter or calculated by the control unit based on tidal volume and respiratory rate settings. Preferably, the control unit is configured to determine the net ventilation of the patient 3 from the current minute ventilation of the patient 3 and information related to leakage in the ventilation system, and to determine the delay in delivery of the oxygen-enriched gas to the patient 3 from the determined volume of the inspiratory line and said net ventilation of the patient 3.

(61) FIGS. 3A and 3B illustrate an exemplary embodiment of a GUI (graphical user interface) that may be caused by the control unit 15 to be displayed on the display unit 29 of the ventilator 1 upon activation of the oxygen boost function by the operator. The GUI comprises three examples of indicators 37A-C which may be displayed separately or in different combinations to indicate the delay in delivery of oxygen-enriched gas to the patient 3. FIG. 3A illustrates the appearance of said indicators 37A-C at a point in time after activation of the oxygen boost function but prior to delivery of the oxygen-enriched gas to the patient, whereas FIG. 3B illustrates the appearance of the indicators 37A-C at a later point in time, during delivery of the oxygen-enriched gas to the patient.

(62) The first indicator 37A is a symbol, such as a circle, which is displayed in a colour selected in dependence of said delay. Upon activation of the oxygen boost function, the control unit 15 causes the indicator 37A to be displayed in a first colour (e.g. red) indicating that the oxygen-enriched breathing gas has not yet reached the patient. After a time period corresponding to said delay, the control unit 15 causes the indicator 37A to switch from the first colour to a second colour (e.g. green) indicating that oxygen-enriched breathing gas is now being delivered to the patient 3. After a yet another time period corresponding to the oxygen boost duration, the control unit causes the indicator 37A to switch back to the first colour to indicate that the patient has received oxygen-enriched breathing gas for the entire oxygen boost duration and that the oxygen concentration of the breathing gas currently being delivered to the patient is back at the baseline level.

(63) The second indicator 37B is a text-based indicator indicating the time remaining to the next substantial change in oxygen concentration of the breathing gas reaching the patient, as determined from said delay. As indicated in FIG. 3A, the second indicator 37B may indicate, after activation of the oxygen boost function but prior to delivery of the oxygen-enriched breathing gas to the patient, the time remaining until a start point in time at which the patient starts to receive oxygen-enriched breathing gas. As indicated in FIG. 3B, the second indicator 37B may also indicate, once the oxygen-enriched breathing gas has started to reach the patient 3, the time remaining to a finish point in time at which the patient has received oxygen-enriched breathing gas during a time period corresponding to the set oxygen boost duration.

(64) The third indicator 37C is an indicator indicating a wash-in-wash-out process of oxygen content in the breathing gas reaching the patient 3, caused by the activation of the oxygen boost function. To this end, the third indicator 37C comprises an elongated field 39 representing a time line, and an indicator 41 indicating the current point in time in relation to said time line. In this exemplary embodiment, the indicator 41 indicating the current point in time moves along the elongated field 39 as time goes by, as indicated by the arrow 43. The elongated field 39 comprises indications of at least a start point in time, t.sub.2, at which breathing gas at said set oxygen boost level (typically 100% oxygen) reaches the patient 3, and a finish point in time, t.sub.3, at which breathing gas at said set oxygen boost level has been delivered to the patient for a time period corresponding to the set oxygen boost duration. The elongated field 39 may further comprise any or any combination of an indication of the point in time, t.sub.0, of activation of the oxygen boost function; an indication of a point in time, t.sub.1, at which the oxygen content in the breathing gas reaching the patient 3 starts to increase from the baseline level towards the set oxygen boost level, and an indication of a point in time, t4, at which the oxygen content in the breathing gas reaching the patient 3 starts to decrease from the set oxygen boost level towards the baseline level. Said indications may for example be provided by causing different areas of the elongated field 39 to be displayed in different colours. An area may in this context be an area of the elongated field 39 between any two of said points in time, t.sub.0-t.sub.4. For example, areas of the elongated field 39 representing delivery to the patient 3 of oxygen concentration at the baseline level (i.e. the area between to and t.sub.1 and the area following t.sub.4) may have one colour, areas of the elongated field 39 representing delivery to the patient 3 of increasing or decreasing oxygen concentration (i.e. the area between t.sub.1 and t.sub.2 and the area between t.sub.3 and t.sub.4) may have another colour, and the area of the elongated field 39 representing delivery to the patient 3 of oxygen concentration at the set oxygen boost level (i.e. the area between t.sub.2 and t.sub.3) may have yet another colour.

(65) FIG. 4 illustrates an exemplary embodiment of a method for providing improved oxygen boost functionality of a ventilator according to the principles of the present disclosure. The method will be described with simultaneous reference to previous drawings.

(66) Steps S1 to S10 (A or B) are typically performed by the control unit 15 of the ventilator during the pre-use check of the ventilator 1, prior to connection of the patient 3 to the ventilator. Steps S11 and S12 are typically performed by the control unit 15 upon activation of the oxygen boost function by an operator of the ventilator.

(67) In the first step S1, gas flow through the proximal and expiratory parts of the patient circuit 5 is prevented. As described above, this may be achieved by the control unit 15 through the display of an instruction to manually occlude the proximal part of the patient circuit on the display unit 29 of the ventilator 1, and closure of the expiratory valve 13 of the ventilator.

(68) In a next step S2, a first gas, typically air, is delivered into the inspiratory line of the patient circuit 15.

(69) In a next step S3, the patient circuit volume, V.sub.pc, i.e. the total volume of the inspiratory line and the expiratory line of the patient circuit, is determined from pressure and volume measurements. As described above, this is typically achieved by determining a pressure-to-volume response of the patient circuit, assuming the compliance, C.sub.pc, of the tubing of the patient circuit to be negligible and taking surrounding pressure, P.sub.amb, into account.

(70) In a next step S4, action is taken to now permit gas flow through the expiratory part of the patient circuit 5, typically by opening said expiratory valve 13 of the ventilator 1.

(71) In a next step S5, a second gas, typically oxygen, is delivered into the inspiratory line of the patient circuit 5.

(72) In a next step S6, a response to the change in gas composition in the patient circuit 5, caused by the introduction of the second gas into the inspiratory line, is determined. As described above, this involves determination of a parameter indicative of the rate of change in gas composition downstream a part of the inspiratory line in which a humidifier may or may not be present.

(73) In a next step S7, typically carried out in parallel with step S6, the resistance of the patient circuit is determined from flow and pressure measurements.

(74) In a next step S8, the type of the patient circuit 5 currently connected to the ventilator 1 is determined from the resistance of the patient circuit 5, determined in step S7.

(75) In a next step S9, it is determined whether the inspiratory line of the patient circuit comprises any humidifier. This determination is made based on the response to the change in gas composition in the patient circuit, determined in step S6. Preferably, it is also made based on the volume of the patient circuit, determined in step S3, taking the type of the patient circuit determined in step S8 into account.

(76) In the next steps S10A and S10B, the volume of the inspiratory line of the patient circuit 5 is determined in dependence of the total volume of the patient circuit 5, determined in step S3, and the presence of any humidifier in the inspiratory line, as determined in step S9.

(77) If no humidifier is determined to be present in step S9, the method continues to step S10A. If, on the other hand, a humidifier is determined to be present, the method continues to step S10B.

(78) In step S10A, the volume of the inspiratory line of the patient circuit is determined to constitute approximately 50% of the total volume of the patient circuit since the inspiratory line volume substantially equals the expiratory line volume in the absence of any humidifier in the inspiratory line.

(79) In step S10B, the volume of the inspiratory line of the patient circuit is determined to constitute the majority part of the total volume of the patient circuit since the presence of a humidifier adds considerable volume to the inspiratory line. As described above, in this scenario, the volume of the inspiratory line may be assumed to constitute e.g. 55%-65% of the total volume of the patient circuit, or be calculated more precisely using e.g. equation 7.

(80) In a next step S11, typically taking place after connection of a patient 3 to the ventilator 1 and upon activation of the oxygen boost function of the ventilator, a delay in delivery of gas from the ventilator to the patient is calculated based on the volume of the inspiratory line, determined in step S10A or S10B. As described above, said delay is typically determined based on the volume of the inspiratory line together with the current minute ventilation (preferably net ventilation) of the patient 3.

(81) In a next step S12, an indication of said delay is communicated to the operator of the ventilator 1, typically through the display of an indicator indicating said delay on a display unit 29 of the ventilator.