System and method for blood gas measurements

Abstract

A system (100) is disclosed, comprising a gas exchange device (110) configured to be coupled to a circulatory system of a patient to transfer a gas component between blood in the circulatory system and a sweep gas passing through the gas exchange device. The system further comprises a valve arrangement (120) configured to selectively couple the gas exchange device to an exchange gas circuit (130) configured be operated as an open circuit providing the sweep gas to the gas exchange device from a gas supply, and a reference gas circuit (140) configured to be operated as a closed circuit recirculating the sweep gas through the gas exchange device. The system further comprises a sensor unit (150) configured to be coupled to the reference gas circuit to generate sensor data indicating a concentration or partial pressure of the gas component in the recirculated sweep gas.

Description

[0001] SYSTEM AND METHOD FOR BLOOD GAS MEASUREMENTS

[0002] Technical Field

[0003] The present invention relates to systems and methods for gas exchange in a circulatory system of a patient, using a gas exchange device. More particularly, the present disclosure concerns techniques for determining a partial pressure of a gas component in the patient’s blood.

[0004] Background

[0005] Gas exchange in blood is a physical process in which gases move through a membrane, such as the blood-air barrier in the alveoli of a mammal lung, to allow oxygen to be taken up by the blood and carbon dioxide to be released from the blood.

[0006] In instances of respiratory failure or when bypassing the patient’s lungs, an external gas exchange device may be employed to either support or replace the lung function. Such devices typically use a sweep gas to oxygenate the blood and facilitate the removal of carbon dioxide from the blood.

[0007] During this process, regular blood sampling may be employed to monitor the blood gas content and assess how effectively the gas exchange device oxygenates the blood and removes carbon dioxide. These blood samples may provide vital information for clinical management, enabling adjustments to the device settings based on the patient’s current gas exchange status and an overall monitoring of the patient’s health.

[0008] Given the critical nature of effective treatment in life-supporting applications, there is a need for enhanced technologies in determining and monitoring blood gas content.

[0009] Summary

[0010] In view of the above, the present disclosure provides an improved or alternative technology having the features set out in the independent claims.

[0011] Hence, according to a first aspect, there is provided a system comprising a gas exchange device configured to be coupled to a circulatory system of a patient to transfer a gas component between blood in the circulatory system and a sweep gas passing through the gas exchange device. The system further comprises a valve arrangement configured to selectively couple the gas exchange device to an exchange gas circuit configured be operated as an open circuit providing the sweep gas to the gas exchange device from a gas supply, and to a reference gas circuit configured to be operated as a closed circuit recirculating the sweep gas through the gas exchange device. The system also comprises a sensor unit configured to be coupled to the reference gas circuit to generate sensor data indicating a concentration or partial pressure of the gas component in the recirculated sweep gas.

[0012] According to a second aspect, there is provided a method for determining a partial pressure of a gas component in blood in a circulatory system of a patient. The method comprises passing a sweep gas through a gas exchange device, circulating the blood through the gas exchange device to allow a gas component to be transferred between the blood and the sweep gas, recirculating the sweep gas, passing through the gas exchange device, in a closed gas circuit comprising a sensor unit generating a sensor signal indicating a concentration or partial pressure of the gas component in the sweep gas, and determining the partial pressure of the gas component in the blood based on the sensor signal.

[0013] In the above aspects, the gas exchange device operates in two different main modes to exchange gases with the blood and to measure blood gas content. Traditionally, these measurements are performed through manual blood sampling, which is relatively resource-intensive and requires additional equipment and consumables. Moreover, manual sampling is typically conducted less frequently, usually only once a day or a few times per day. The proposed approach represents an improvement by streamlining these processes and allows for an increase in frequency of measurements.

[0014] Increasing the frequency of these measurements may enhance the time resolution of the collected data, allowing for more precise monitoring of the patient’s status. Additionally, this may enable timelier adjustments to the gas exchange settings. By capturing changes in the patient’s blood gas levels more rapidly, clinicians can respond more effectively to the patient’s evolving needs, optimising therapeutic outcomes. Thus, higher time resolution facilitates closer monitoring and more accurate management of the gas exchange process, ensuring that adjustments to the device are both appropriate and timely.

[0015] The blood gas measurements utilise an equilibrium approach, where the sweep gas is temporarily recirculated within the reference gas circuit to allow it to equilibrate with the partial pressure of the gas components in the blood. Experiments show that the transient phase before reaching a sufficient level of equilibrium is notably brief, typically lasting 60 seconds or less, such as 30 seconds or less. After this period, sensor unit readings may accurately reflect the blood gas levels to a satisfactory degree. The brevity of this phase has been found to not significantly interfere with the gas exchange with the blood. Consequently, the valve arrangement may promptly revert the gas exchange device to its normal operation by switching it back to the exchange gas circuit.

[0016] The sensor unit may comprise a sensor for generating data indicating a composition of the reference sweep gas, such as a concentration or partial pressure of the gas component in the reference sweep gas. Specifically, the data may indicate information about in what amounts or proportions oxygen or carbon dioxide are present in the sweep gas. Hence, the sensor unit may comprise an oxygen sensor and / or a carbon dioxide sensor. Depending on the specific gas component required for measurement, other types of sensors might be utilised either in conjunction with or as a replacement for these sensors. Each of these sensors may be communicatively linked to a control unit utilising these signals for calculating the concentrations and partial pressures of the gas components.

[0017] In some examples, the sensor unit comprises a pump for recirculating the sweep gas in the closed circuit. The pump may be employed to provide a continuous and controlled flow of the sweep gas, allowing for improved accuracy and stability of the measurement. By maintaining a consistent circulation of sweep gas, the pump aids in quickly achieving equilibrium between the sweep gas and the blood gas components.

[0018] The system may further comprise a gas reservoir configured to be coupled to the reference gas circuit, thereby increasing a volume of the recirculated gas. This reservoir may have a variable volume to accommodate volume changes of the recirculated gas and reduce pressure fluctuations in the reference gas circuit. Furthermore, increasing the total volume of the recirculated sweep gas may help stabilising the partial pressure of gas components within the system. A larger volume may serve to dilute fluctuations in partial pressure resulting from the gas exchange, enhancing the system’s resilience to changes in specific gas components and ensuring more consistent measurements. Additionally, an increased gas volume may permit longer measurement cycles without significantly interfering with the ongoing gas exchange with the blood. Examples of such a reservoir include flexible tanks, expandable bladders, and bellows.

[0019] Several types of membranes can be employed in the gas exchange device to transfer the gas component between the blood and the sweep gas. In an example, the gas exchange device comprises a fibre-based membrane, in which the blood may flow inside hollow fibres and the sweep gas outside the fibres. In alternative designs, the sweep gas may flow inside the fibres and the blood outside the fibres. Oxygen and carbon dioxide exchange may occur across the membrane formed by the walls of the hollow fibres.

[0020] During the initial phase of the measurement mode, there may be a transient phase where the partial pressures of gases in the blood and the sweep gas come into balance. More specifically, each gas component seeks to equalise its partial pressure between the blood and the sweep gas. The rate at which the adjustment happens typically depends on the diffusion rate across the membrane of the gas exchange device, the membrane surface area, as well as temperature and pressure within the gas exchange device. By monitoring a change in the partial pressure or the concentration of the gas component as a function of time during this initial phase, it may be possible to determine a status, or gas transfer capacity, of the gas exchange device. This may, for example, be realised by determining a time constant associated with the change and compare the time constant with a reference time constant. If the change rate in partial pressure or concentration is lower than expected, this may indicate a malfunction of the gas exchange device. The gas transfer capacity of the membrane may, for example, decline over time due to accumulation of blood clots, deposition of a layer increasing diffusion resistance, and water vapour condensing inside and blocking the fibres of the membrane. The reference time constant may correspond to an ideal gas transfer capacity, such as the expected gas transfer capacity of the gas exchange device assuming it is in pristine condition, without wear or deterioration. If the monitored gas transfer capacity falls outside acceptable limits, this indicates the need for replacement. A warning or error signal may be issued, prompting operator intervention.

[0021] A series of measurements taken across multiple initial phases can be utilised to determine the gas transfer capacity of the gas exchange device. This approach may, for example, involve monitoring changes in the concentration or partial pressure of the gas component during these phases. By analysing these changes over time, it may be possible to detect any malfunctions in the gas exchange device or to estimate a time for its replacement.

[0022] In some examples, the change rate may be employed to identify when the system has reached equilibrium, i.e., when the gas component concentration gradients or partial pressures have been reduced to a minimum across the membrane. This equilibrium phase may be indicated by the concentration change rate or partial pressure change rate dropping below a specified threshold. It may then be concluded that the measurements of the gas component concentrations or partial pressures in the sweep gas accurately reflect the partial pressures of the blood gas components in the blood.

[0023] In further examples, the change rate may be used to approximate or extrapolate a steady state level of the gas components, potentially saving time by eliminating the need to wait for actual equilibration.

[0024] In the present disclosure, the term ‘gas exchange device’ may also be referred to as a ‘gas transfer unit’, ‘artificial lung’, ‘membrane lung’, or ‘oxygenator’.

[0025] Typically, the gas exchange device is configured to connect to the patient’s circulatory system via an extracorporeal circuit. This circuit is a medical setup that routes blood outside the patient’s body. As part of this setup, the gas exchange device may work in conjunction with pumps, tubing, heat exchangers, and other components necessary to either take over or support the function of the patient’s lungs.

[0026] By ‘sweep gas’ is typically understood a gas that is passed through the gas exchange device to facilitate the exchange of gases, such as oxygen and carbon dioxide. The sweep gas often comprises a controlled mixture of oxygen and in some cases carbon dioxide at proportions ensuring the proper balance of respiratory gases in the blood. The gas composition of the sweep gas may be adjusted, for example by a gas mixer or blender, based on the concentration or partial pressure of the gas component(s) determined based on the sensor data. Thus, the sensor data obtained by recirculating the sweep gas through the gas exchange device can serve as feedback for controlling the gas composition of the sweep gas supplied to the exchange gas circuit.

[0027] The exchange gas circuit can be described as an open circuit, wherein the gas exchange device is supplied with a flow of ‘fresh’ sweep gas. Once the sweep gas has passed through the gas exchange device, interacting with the blood to facilitate gas exchange, the gas may be expelled from the device and not reused. In contrast, the reference gas circuit may operate as a closed circuit. In this setup, the used sweep gas is not expelled but recirculated back through the gas exchange device.

[0028] The term ‘gas component’ refers to any individual gas that is part of a mixture of gases, such as the sweep gas or gases present in the blood. Examples include oxygen and carbon dioxide, as well as nitrogen, various anaesthetic agents, and other physiologically relevant trace gases that may be present in the blood.

[0029] Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

[0030] Brief Description of the Drawings

[0031] The above, as well as additional objects, features, and advantages of the present disclosure will be better understood through the following illustrative and non-limiting detailed description of examples, with reference to the appended drawings. Same reference numerals will be used for similar elements.

[0032] Figure 1 shows a gas exchange device coupled to a circulatory system of a patient.

[0033] Figure 2 shows a system according to an embodiment, comprising an exchange gas circuit providing sweep gas to a gas exchange device, and a reference gas circuit recirculating the sweep gas through the gas exchange device.

[0034] Figure 3 is a flow chart illustrating a method for determining a partial pressure of a gas component according to an embodiment.

[0035] As illustrated in the figures, the sizes of the elements and features may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the examples. Detailed Description

[0036] Figure 1 shows by way of example a system 100 for exchanging one or more gases with blood in a circulatory system of a patient 10. The system 100 comprises a gas exchange device 110 for transferring blood gases between blood and a sweep gas, wherein the blood is circulated in an extracorporeal circuit 105 and the sweep gas is passed through the gas exchange device 110.

[0037] Examples of systems 100 according to the present disclosure include cardiopulmonary bypass machines (heart-lung machines) providing circulatory and respiratory support in the operating theatre while the heart is stopped for surgery. Further examples include extracorporeal membrane oxygenation (ECMO) devices providing circulatory and respiratory support in intensive care units, and extracorporeal carbon dioxide removal (ECCO2R) devices removing carbon dioxide from the blood.

[0038] The gas exchange device 110 is configured to facilitate exchange of gases between the patient’s blood and a sweep gas passing through the gas exchange device 110. Typically, the gas exchange device 110 is configured to allow oxygen to pass from the sweep gas into the blood, thereby oxygenating the blood, and to allow carbon dioxide to be released from the blood and pass into the sweep gas. It will be appreciated that other types of gases and substances may be exchanged in a similar way, including anaesthetic agents and nitric oxide.

[0039] The gas exchange device 110 may comprise a gas region 114 and a blood region 116 separated by a gas-permeable membrane 112. The blood in the extracorporeal circuit 105 may be circulated through the blood region 116 by a circulation unit 107, or pump, whereas the sweep gas may be supplied to the gas region 114 by means of a gas blender 132. Due to a partial pressure gradient, or a concentration difference, between individual components of the sweep gas and the corresponding component in the blood, this component may be passed through the membrane 112 from the gas region 114 into the blood region 116 or vice versa. In particular, oxygen may be passed from the gas region 114 to the blood region 116 through the membrane 112 so that the oxygen-poor, or venous, blood is oxygenated into oxygen-rich, or arterial, blood. Vice versa, carbon dioxide may be passed from the blood region 116 to the gas region 114 through the membrane 112 so that carbon dioxide is removed from the flow of blood. Other gas components like anaesthetic gases present in the sweep gas or the blood may flow across the membrane as well.

[0040] Several types of membranes 112 may be employed. In an example, the gas exchange device 110 comprises a hollow fibre membrane, in which the blood flows in the blood region 116 inside the fibres and the gas mixture flows in the gas region 114 outside the fibres. Oxygen and carbon dioxide exchange may occur across the membrane formed by the walls of the hollow fibres. In the example illustrated in figure 1, however, the membrane 112 is schematically illustrated as a sheet membrane.

[0041] The circulation unit 107 may, for example, comprise a roller pump or a centrifugal pump, depending on the specific type of system 100. Roller pumps typically comprises a rotating roller compressing a flexible tube or membrane. As the roller rotates, it squeezes the tube, creating a pulsatile flow of blood. Centrifugal pumps, on the other hand, use a rapidly rotating impeller to create a centrifugal force which pushes the blood outwards to generate a substantially continuous blood flow. Centrifugal pumps have been observed to reduce the risk for haemolysis, i.e., breakdown of red blood cells, and improve patient comfort.

[0042] The transfer capacity of oxygen or carbon dioxide, i.e., the amount of oxygen or carbon dioxide which is supplied to or removed from the flow of blood per unit of time depends, inter alia, on the flow rate of the blood, the flow rate of the sweep gas, the composition of the sweep gas, and the state of the gas exchange device 110 itself. In particular, the gas transfer capacity of the membrane 112 can decline over time due to accumulation of blood clots, deposition of a layer increasing diffusion resistance, and water vapour condensing inside and blocking the hollow fibres of the membrane 112. A gas exchange device 110 incapable of oxygenating the blood to a satisfying degree may hence be considered to be in a degraded or error state.

[0043] The sweep gas may be provided by a gas blender 132. Typically, the gas blender 132 comprises a plurality of inlets configured to receive medical gas Pl, P2 from a respective gas source (not shown). Medical oxygen may be supplied to the gas blender 132 from an oxygen source, which may be an oxygen outlet of a central medical gas system of a hospital facility, a pressurised gas cylinder, or any other type of oxygen source suitable for delivering oxygen for medical applications. The same applies to air, which may be supplied from a pressurised air outlet of a central medical gas system of a hospital facility, a pressurised cylinder, or retrieved and pressurised from the surrounding air.

[0044] The gases may be mixed into a sweep gas mixture by the gas blender 132 and supplied to the gas exchange device 110. The composition and flow rate of the sweep gas may be adjusted according to the patient’s needs, allowing healthcare professionals to control the oxygen levels delivered to the patient 10. The gas blender 132 may be electronically controlled, and in some examples configured to utilise sensor input to achieve the accurate gas composition and flow rate.

[0045] Figure 2 is a schematic illustration of a system 100 according to some examples. The depicted system 100 may be configured similarly to the system 100 discussed above in connection with figure 1. Hence, the system 100 may comprise a gas exchange device 110 configured to be coupled to a circulatory system of the patient (not shown) to transfer a gas component, such as oxygen and carbon dioxide, between the patient’s blood and a sweep gas passing through the gas exchange device 110. In figure 2, the extracorporeal circuit is indicated by circuit tubing 106, to which the gas exchange device 110 is connected.

[0046] The sweep gas may be routed through two different circuits: an exchange gas circuit 130, which supplies fresh sweep gas from the gas blender 132 to the gas exchange device 110, and a reference gas circuit 140, which recirculates the sweep gas through the gas exchange device 110. This recirculation allows for the equilibration of gas components between the sweep gas and the blood. In different words, the exchange gas circuit 130 may be considered to form an open circuit configuration, in which the sweep gas passes through the circuit 130 and is replaced by new gas, whereas the reference gas circuit 140 may be of a closed configuration in which substantially the same gas is circulated through the gas exchange device 110 and not replaced by new gas.

[0047] A valve arrangement 120 is provided to selectively couple the gas exchange device to the exchange gas circuit 130 and the reference gas circuit 140. The valve arrangement may comprise a first valve arranged upstream of the gas exchange device 110 to control the flow of sweep gas supplied to the gas exchange device 110, and a second valve arranged downstream of the gas exchange device 110 to control the flow of sweep gas leaving the gas exchange device 110. Each of the valves may be of a two- way valve type, which is operable to selectively direct the sweep gas either towards the exchange gas circuit 130 for ‘normal’ operation of the gas exchange device 110, such as oxygenation of the blood, or towards the reference gas circuit 140 for recirculation. Each valve can switch between opening to one circuit while closing off the other.

[0048] The valve arrangement 120 allows for the gas exchange device 110 to be operated in two different modes: a standard operation mode, or exchange mode, in which the valve arrangement 120 opens to allow fresh sweep gas from the gas blender 132 into the gas exchange device 110 via the exchange gas circuit 130, and a measurement mode, or recirculation mode, in which the valve arrangement 120 switches to direct the sweep gas through the reference gas circuit 140 to allow it to recirculate through the gas exchange device 110. This mode is a temporary mode, used to equilibrate the gas components to promote determination of a partial pressure of one or more gas components in the blood. During a typical operation, the gas exchange device 110 may be temporarily shut off from the flow of sweep gas delivered by the gas blender 132 and switched to the reference gas circuit for a relatively short time, such as 60 seconds or less, to allow the blood gas content in the circulating sweep gas to be analysed.

[0049] The system 100 includes a sensor unit 150 coupled to the reference gas circuit 140 to generate data indicating a concentration or partial pressure of one or more gas components in the recirculated sweep gas. The valve arrangement 120 may be configured to disconnect the gas exchange device 120 from the sweep gas supply, such as the gas blender 132, and instead connect it in series with the sensor unit 150. Consequently, the gas exchange device 110, the sensor unit 150, and the connecting tubing may collectively form the reference gas circuit 140. This setup allows for the recirculation of sweep gas during the measurement mode.

[0050] The sensor unit 150 according to the present example comprises an oxygen sensor 152 arranged to interact with the sweep gas flow to measure the oxygen concentration or partial pressure. Examples of oxygen sensors 152 include electrochemical sensors and optical sensors. Furthermore, the sensor unit 150 comprises a carbon dioxide sensor 154 arranged to measure the carbon dioxide concentration or partial pressure in the sweep gas flow. Examples of carbon dioxide sensors include infrared (IR) sensors correlating the level of absorption of infrared light by carbon dioxide molecules to the concentration of carbon dioxide molecules in the sweep gas.

[0051] The sensors 152, 154 may be components of a gas analyser device, which can either be a standalone unit connected to the reference gas circuit 140 via tubing or integrated directly within the gas exchange device 110. In alternative configurations, one or more of these sensors 152, 154 may be deployed as independent units linked to the reference gas circuit 140.

[0052] A pump 156 may be provided for recirculating the sweep gas in the closed circuit formed by the reference gas circuit 140. Examples of pumps include diaphragm pumps and piston pumps. In the present example, the pump 156 is integrated in the sensor unit 150, or gas analyser. However, in alternative configurations, the pump 156 may be a standalone unit coupled to the reference gas circuit 140.

[0053] The sensors 152, 154 are communicatively coupled to a control unit 160 for processing of the sensor data generated by the sensors 152, 154. The control unit 160 may be incorporated in the sensor unit 150 or the gas exchange device 110, or arranged at another location, physically separate from the sensor unit 150 and the gas exchange device 110. Further, the control unit 160 may be arranged to control the operation of the valve arrangement 120 to allow the system 100 to automatically switch between the standard operation mode and the measurement mode.

[0054] The output from the control unit 160 may be utilised to control the operation of the gas blender 132. Feedback from the sensor unit 150, which measures the partial pressures or concentrations of gases like oxygen and carbon dioxide in the recirculated sweep gas, which is equilibrating with the partial pressure of gases in the blood, provides adjustments to the composition and flow rate of the sweep gas supplied by the gas blender to the gas exchange device 110. For instance, if the sensor data indicates a deficiency in oxygen level in the blood, the control unit 160 can instruct the gas blender 132 to increase the oxygen proportion in the sweep gas, ensuring desired blood gas levels are maintained. Similarly, if the sensor data indicate too high levels of carbon dioxide in the blood, the control unit 160 can instruct the gas blender 132 to increase the flow of the sweep gas, or, if applicable, reducing the carbon dioxide proportion in the sweep gas. An example of a method for determining a partial pressure of a gas component in the blood is illustrated in the flow chart of figure 3. The method may be performed in a system configured similarly to the one disclosed in figure 2. According to figure 3, the sweep gas is passed 210 through the gas exchange device 110 while the blood is circulated 220 through the same to allow one or more gas components, such as oxygen and carbon dioxide, to be transferred through the membrane 112 of the gas exchange device 110. In a typical use case, oxygen is transferred from the sweep gas to oxygenate the blood, while carbon dioxide may be released from the blood and discharged from the gas exchange device 110 through the sweep gas flow. This may be referred to as the standard operation mode, or gas exchange mode, of the gas exchange device 110, in which the gas exchange device 110 is coupled to the exchange gas circuit 130 to provide fresh sweep gas in an open circuit configuration.

[0055] In another step, the sweep gas is recirculated 230 within the exchange gas circuit 130, which is operated as a closed gas circuit 140 to allow the partial pressures of the gas components in the blood and the recirculated sweep gas to equilibrate. This process is part of the measurement mode of the gas exchange device 110, during which substantially the same volume of sweep gas continuously circulates through the gas exchange device 110. Gas exchange continues across the membrane 112 in a manner similar to the standard operation mode. However, a difference is that the sweep gas is not replenished. Over time, this leads to a gradual decrease in the concentration differences, or differences in partial pressure, between the gas components in the recirculated sweep gas and those in the blood. Eventually, the concentrations or partial pressures in the recirculated sweep gas stabilise in an equilibrium phase and can be considered representative of the partial pressures of the respective gas components in the blood.

[0056] The sensor unit 150, which in this example is integrated into the reference gas circuit 140, generates 240 a sensor signal that indicates the concentrations or partial pressures of various gas components in the recirculating sweep gas. This sensor signal may be transmitted to the control unit 160, which processes the signal to determine 250 the partial pressure of these gas components in the blood. In one approach, it is assumed that the gas components have equilibrated across the membrane 112. This assumption allows the control unit 160 to equate the concentrations or partial pressures of oxygen and carbon dioxide in the recirculated sweep gas with their respective partial pressures in the blood. Typically, this approach may be applied when the measurement mode extends over a relatively long duration, such as about 30 seconds, providing a high degree of confidence that equilibration has been adequately achieved.

[0057] It is also possible to monitor the change rate in the gas component concentrations or partial pressures over time. Specifically, during the transient phase after switching to the measurement mode, this rate can be analysed to identify when the system reaches equilibrium. The rate of approach to this equilibrium may be modelled using exponential decay functions, or negative exponential models, characterised by a time constant and an asymptotic approach towards equilibrium. The time constant and the asymptote can be used to gain information about the system and to estimate the blood gas values.

[0058] The time constant can be used to predict when the system is close enough to equilibrium (the asymptote) to accurately reflect the blood gases. By monitoring the rate of change and comparing it to the modelled asymptotic approach, it may be possible to determine when the changes have slowed to within a threshold that is considered practically stable or equilibrated. This means that once the change rate in the gas component’s concentrations or partial pressures drops below a certain threshold - indicating that the values are approaching the asymptote - it may be assumed that the values have stabilised. Thus, further measurement can be considered to reliably reflect the blood gas values, facilitating quicker and potentially more frequent assessments without waiting for full equilibrium.

[0059] In further examples, the exponential decay model may be used to determine or predict the asymptote, which may serve as an estimate of the concentration or partial pressures in the blood.

[0060] Moreover, the rate at which the equilibrium is approached (as evidenced by the time constant) may serve as an indicator of the gas exchange device’s 110 health. A slower than expected approach can signal potential malfunctions. For instance, if the rate of change in the gas component concentration or partial pressure in the sweep gas is slower than expected, it may suggest a diminished gas transfer capacity of the membrane 112. This diminished capacity could result from factors such as the accumulation of blood clots, deposition increasing diffusion resistance, or condensation blocking the membrane’s fibres. The reference time constant may align with the ideal gas transfer capacity expected from a pristine device. Deviations from this standard may necessitate a replacement of parts, and a warning or error signal could be issued to prompt operator intervention.

[0061] A series of measurements taken across multiple initial phases can also be utilised to determine the gas transfer capacity of the gas exchange device 110. This approach may, for example, involve monitoring changes in the concentration or partial pressure of the gas component during these phases. By analysing these changes over time, it may be possible to detect any malfunctions in the gas exchange device 110 or to estimate a time for its replacement

[0062] By alternating between the standard operation mode and the measurement mode, the blood gas content and patient’s status, as well as the functionality of the gas exchange process, can be monitored regularly without the need for manual blood sampling. Moreover, by engaging the measurement for brief periods - typically less than 1 minute, or even less than 30 seconds - the measurements can be conducted without significantly disrupting the primary gas exchange functions.

[0063] The control unit 160 of the present disclosure may generally comprise one or more processors and one or more non-transitory computer-readable media storing first computer executable instructions that, when executed by the one or more processors, cause the system 100 to perform at least parts of the actions shown in figure 3 and described above. Generally, the control unit 160 may comprise circuitry which is configured to implement (using one or more non-transitory computer-readable media) the functionality described herein. Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors or cores, of any kind of computer. The processors can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). Those skilled in the art will understand that the above-described exemplary embodiments may be implemented in any suitable software, hardware, or firmware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Windows OS, a Mac platform and MAC OS, a mobile device having an operating system such as iOS, Android, etc. In a further example, the exemplary embodiments of the abovedescribed method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practising the claimed invention, from a study of the drawing, the disclosure, and the appended claims. Moreover, in the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. The scope of the invention is set forth in the following claims, in which the word ‘comprising’ does not exclude other elements or steps, and the indefinite article ‘a’ or ‘an’ does not exclude a plurality.

Claims

CLAIMS1. A system (100) comprising: a gas exchange device (110) configured to be coupled to a circulatory system of a patient to transfer a gas component between blood in the circulatory system and a sweep gas passing through the gas exchange device; a valve arrangement (120) configured to selectively couple the gas exchange device to: an exchange gas circuit (130) configured be operated as an open circuit providing the sweep gas to the gas exchange device from a gas supply, and a reference gas circuit (140) configured to be operated as a closed circuit recirculating the sweep gas through the gas exchange device; the system further comprising a sensor unit (150) configured to be coupled to the reference gas circuit to generate sensor data indicating a concentration or partial pressure of the gas component in the recirculated sweep gas.

2. The system according to claim 1, wherein the sensor unit comprises at least one of: an oxygen sensor (152) for generating sensor data indicating a concentration or partial pressure of oxygen in the sweep gas, and a carbon dioxide sensor (154) for generating sensor data indicating a concentration or partial pressure of carbon dioxide in the sweep gas.

3. The system according to claim 1 or 2, wherein the sensor unit comprises a pump (156) for circulating the sweep gas in the closed circuit.

4. The system according to any of the preceding claims, further comprising a gas reservoir configured to be coupled to the reference gas circuit to increase a volume of the recirculated sweep gas.

5. The system according to claim 4, wherein the gas reservoir comprises a bellows.

6. The system according to any of the preceding claims, wherein the gas exchange device comprises a fibre-based membrane (112) for transferring the gas component between the blood and the sweep gas.

7. A method for determining a partial pressure of a gas component in blood in a circulatory system of a patient, comprising: passing (210) a sweep gas through a gas exchange device; circulating (220) the blood through the gas exchange device to allow a gas component to be transferred between the blood and the sweep gas; recirculating (230) the sweep gas, passing through the gas exchange device, in a closed gas circuit comprising a sensor unit; generating (240), by means of the sensor unit, a sensor signal indicating a concentration or partial pressure of the gas component in the sweep gas; and determining (250) the partial pressure of the gas component in the blood based on the sensor signal.

8. The method according to claim 7, comprising: operating the gas exchange device in a standard operation mode, in which the gas exchange device is provided with fresh sweep gas from a gas supply, using an open gas circuit; operating the gas exchange device in a measurement mode in which the sweep gas is recirculated through the closed gas circuit; and selectively switching the gas exchange device between the standard operation mode and the measurement mode.

9. The method according to claim 8, comprising operating the gas exchange device in the measurement mode for less than 1 minute before switching back to the standard operation mode.

10. The method according to claim 8 or 9, comprising: monitoring a change in the concentration or partial pressure of the gas component during an initial phase of the measurement mode;determining a time constant associated with the change; and determining a status of the gas exchange device based on the time constant.

11. The method according to claim 8, comprising: determining a change rate in the concentration or partial pressure of the gas component during the measurement mode; determining an equilibrium phase in which the change rate is below a predetermined change rate threshold; and determining the concentration or partial pressure of the gas component during the equilibrium phase.

12. The method according to claim 8, comprising: determining a change rate in the concentration or partial pressure of the gas component during the measurement mode; estimating, based on the change rate, a concentration or partial pressure of the gas component in an equilibrium phase; and determining the partial pressure of the gas component based on the estimated concentration or partial pressure.

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