System and method for blood gas measurements

Abstract

A system (100) is disclosed, comprising a fluid exchange module (110) configured to be coupled to an extracorporeal circuit (105), circulating blood of a circulatory system of a patient, to transfer a fluid component between the blood and an exchange medium flowing through the fluid exchange module. The system further comprises a gas exchange device (120) configured to be coupled to the extracorporeal circuit to transfer a gas component between the blood and a reference sweep gas passing through the gas exchange device, a reference gas circuit (130) configured to be operated as a closed circuit recirculating the reference sweep gas through the gas exchange device, and a sensor unit (140) 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 reference sweep gas.

Description

[0001] SYSTEM AND METHOD FOR BLOOD GAS MEASUREMENTS

[0002] Technical Field

[0003] The present invention relates to systems and methods for fluid transfer in a circulatory system of a patient. More particularly, the present disclosure concerns a fluid exchange module for transferring a fluid component between the patient’s blood and an exchange medium, as well as a gas exchange device for measuring a partial pressure of a gas component in the blood.

[0004] Background

[0005] Gas exchange in blood is a physical process where blood gases move through a membrane, such as the blood-air barrier in the alveoli of mammalian lungs. This process allows oxygen to be taken up by the blood and carbon dioxide to be released. Monitoring blood gas content is vital for patient care in clinical settings. Traditionally, blood gas measurements are performed through manual blood sampling and off-line analysis, either using a blood gas analyser available at the point of care or in a centralised laboratory. This type of measurements is relatively resource-intensive and typically requires additional equipment and consumables. As a result, manual sampling is often conducted infrequently, usually once a day or a few times per day.

[0006] Increasing the frequency of these measurements could allow for more precise monitoring of a patient’s status and evolving needs. Therefore, there is a need for improved technologies to enhance the determination and monitoring of the blood gas content.

[0007] Summary

[0008] In view of the above, the present disclosure provides an improved or alternative technology having the features set out in the independent claims.

[0009] Hence, according to a first aspect, there is provided a system comprising a fluid exchange module configured to be coupled to an extracorporeal circuit, circulating blood of a circulatory system of a patient, to transfer a fluid component between the blood and an exchange medium flowing through the fluid exchange module. The system further comprises a gas exchange device, a reference gas circuit, and a sensor unit. The gas exchange device is configured to be coupled to the extracorporeal circuit to transfer a gas component between the blood and a reference sweep gas passing through the gas exchange device. The reference gas circuit is configured to be operated as a closed circuit recirculating the reference sweep gas flow through the gas exchange device, and the sensor unit is 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 reference sweep gas.

[0010] 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 the blood and an exchange medium through a fluid exchange module device to transfer a fluid component between the blood and the exchange medium, passing the blood and a reference sweep gas through a gas exchange device to transfer the gas component between the blood and the reference sweep gas flow, recirculating the reference sweep gas flow, passing through the gas exchange device, in a closed circuit comprising a sensor unit generating a sensor signal indicating a concentration or partial pressure of the gas component in the reference sweep gas flow, and determining the partial pressure of the gas component in the blood based on the sensor signal.

[0011] In the above aspects, an equilibrium approach is utilised, where the reference sweep gas is recirculated through the gas exchange device to allow the reference sweep gas to equilibrate with the partial pressures of the gas components in the blood. Each gas component naturally seeks to equalise its partial pressure between the blood and the reference sweep gas, leading to a gradual decrease in the partial pressure differences. Eventually, the partial pressures in the recirculated gas may stabilise and can be considered to accurately reflect the partial pressures of the respective gas components in the blood. This method makes it possible to determine the blood gas content by measuring the gas component concentrations or partial pressures in the recirculated sweep gas, eliminating the need for direct blood measurement. The gas component concentrations or partial pressures may be measured directly in the equilibrated state or approximated based on a change rate of the concentrations or partial pressures during a transient phase. The gas exchange device is configured to be coupled to an extracorporeal circuit, which may be used in various medical treatments and procedures including dialysis, extracorporeal membrane oxygenation (ECMO), and cardiopulmonary bypass (CPB). These procedures typically involve a fluid exchange module, where fluid components such as blood gases or waste products are transferred between the blood and an exchange medium flowing through the fluid exchange module. By coupling the gas exchange device to the extracorporeal circuit, the partial pressures of the blood gas components may be determined based on sensor measurements performed on the reference sweep gas recirculating through the gas exchange device. In other words, the gas exchange device may act as an ‘add-on’ module, providing blood gas measurement capabilities to the medical treatment or procedure performed on the blood circulating in the extracorporeal circuit. The gas exchange device may be connected to the extracorporeal circuit at a position upstream of the fluid exchange module to measure the blood gas content pre-fluid exchange, or downstream of the fluid exchange module to measure the blood gas content post-fluid exchange.

[0012] The present disclosure may be employed to measure partial pressure of various gases in the blood, such as oxygen, carbon dioxide, and anaesthetic agents. It may be of particular interest to monitor anaesthetic agents when an oxygenator is used in conjunction with sedation in the ICU or when the patient is anaesthetised during heartlung procedures in the operating room. The partial pressure of anaesthetic agents is often a good estimate of the depth of anaesthesia.

[0013] As mentioned above, the gas exchange module may be used in conjunction with oxygenation or dialysis. The fluid exchange module may therefore include a dialysis membrane, with the exchange medium being a dialysate. The fluid exchange module typically operates by filtering waste products, excess fluids, and toxins from blood when the patient’s kidneys are unable to perform these functions effectively. The process involves passing the blood and the dialysate through the fluid exchange module, allowing waste products, excess fluids, and toxins to diffuse across the dialysis membrane into the dialysate. By placing the gas exchange device either upstream or downstream of the fluid exchange module, the partial pressures of the blood gas components, such as carbon dioxide and oxygen, may be monitored during dialysis. In other examples, the gas exchange module may be used in conjunction with oxygenation procedures, such as ECMO or CPB. In these cases, the fluid exchange module may include a gas transfer membrane, with the exchange medium being an exchange sweep gas. The fluid exchange module allows blood gas components, such as oxygen and carbon dioxide, to be exchanged between the sweep gas and the blood due to concentration differences or partial pressure gradients across the gas transfer membrane. By coupling the gas exchange device to the blood flow through the fluid exchange module, the gas content in the blood can be monitored during the oxygenation process.

[0014] This approach beneficially allows for continuous monitoring of the patient’s status and the efficiency of gas exchange in the blood, providing an improvement over traditional, manual blood sampling, which is typically conducted less frequently due to practical constraints. 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. 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] Several types of membranes can be employed in the fluid exchange module to transfer the fluid component between the blood and the fluid exchange medium. In some examples, both the dialysis membrane and the gas transfer membrane may comprise a fibre-based membrane, in which the blood may flow inside hollow fibres and the fluid exchange medium (such as the dialysate or the exchange sweep gas) outside the fibres. In alternative designs, the fluid exchange medium may flow inside the fibres and the blood outside the fibres. The exchange of fluid components may occur across the membrane formed by the walls of the hollow fibres.

[0016] The same applies to the gas exchange device, which may comprise a gas transfer membrane being, for example, a fibre-based membrane.

[0017] In some examples, the gas exchange device may be selectively coupled to the same gas flow as the fluid exchange module, such that both devices receive sweep gas from a common gas supply. This can be achieved using an exchange gas circuit and a valve arrangement. The exchange gas circuit is operable as an open circuit, providing sweep gas (exchange sweep gas) to the fluid exchange module from the gas supply, while the valve arrangement is operable to selectively couple the gas exchange device to either the exchange gas circuit or the reference gas circuit.

[0018] This configuration allows the gas exchange device to operate in different modes: a measurement mode, in which the sweep gas is recirculated as a reference sweep gas, allowing it to equilibrate with the blood gases and enable measurements of the partial pressures of the blood gases, and an exchange mode in which the gas exchange device receives fresh sweep gas (exchange sweep gas) to contribute to the oxygenation of the blood. Thus, the gas exchange device may have a dual functionality, participating in the oxygenation process when not used for blood gas measurements.

[0019] In some examples, the fluid exchange module and the gas exchange device are structurally separate units, meaning the gas exchange device can function as a standalone device rather than forming an integrated part of the fluid exchange module. This allows for flexibility in the system configuration and integration with existing equipment for extracorporeal circuits.

[0020] In other examples, the gas exchange device maybe integrated the fluid exchange module, forming a single, unified unit. Both the fluid exchange module and the gas exchange device may be housed within the same module, facilitating handling and compact design.

[0021] In some examples, the fluid exchange module and the gas exchange device may form separate compartments within a common gas exchange arrangement. The common gas exchange arrangement may comprise various inlets and outlets for guiding the blood and the respective sweep gas flows through the gas exchange arrangement. A blood inlet and a blood outlet may be provided to guide the blood through the respective compartments, a first gas inlet and a first gas outlet may be provided for guiding the exchange sweep gas through the fluid exchange module, and a second gas inlet and a second gas outlet may be provided for guiding the reference sweep gas through the gas exchange device. As mentioned above, the exchange sweep gas and the reference sweep gas may originate from separate gas sources or from the same gas source. In the latter case, the reference sweep gas may be provided by switching the second gas inlet from the common gas source to the reference gas circuit to allow the gas to recirculate through the gas exchange device during the measurement mode. 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

[0022] 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 reference 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.

[0023] In some examples, the sensor unit is configured to measure the concentration or partial pressure of the gas component in the exchange gas circuit, i.e., in the sweep gas leaving the gas exchange device, as well as in the reference gas circuit. This allows the sensor unit to be utilised to determine the partial pressure of the gas component in the blood when the gas exchange device is operated in measurement mode, and to determine effluent gas concentrations or partial pressures when the gas exchange device is operated in standard operation mode. To facilitate this dual functionality, the sensor unit may be arranged between an outlet of the gas exchange device and the valve arrangement. This placement allows the sweep gas to pass through the sensor unit in both operational modes, allowing continuous monitoring of gas parameters. In some examples, the sensor unit comprises a pump for recirculating the reference sweep gas in the closed circuit. The pump may be employed to provide a continuous and controlled flow of the reference sweep gas, allowing for improved accuracy and stability of the measurements. By maintaining a consistent circulation of reference sweep gas, the pump aids in quickly achieving equilibrium between the reference sweep gas and the blood gas components.

[0024] 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 reference sweep gas come into balance. More specifically, each gas component seeks to equalise its partial pressure between the blood and the reference 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 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.

[0025] 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.

[0026] 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 pressure differences 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 reference sweep gas accurately reflect the partial pressures of the blood gas components in the blood.

[0027] 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.

[0028] In the present disclosure, the term ‘fluid exchange module’ typically refers to a device capable of exchanging one or more fluid components between a fluid exchange medium and the patient’s blood. The fluid components may include gases, such as blood gases or anaesthetic agents, and liquids such as waste products, excess fluids, and toxins removed during dialysis. The fluid components are exchanged between the blood and the fluid exchange medium, which is understood to include a gas flow (such as the sweep gas used in oxygenation) or a liquid flow (such as the dialysate used in dialysis).

[0029] By ‘gas exchange device’ is meant a device or component used to exchange one or more gas component between the blood and a gas flow to enable the gas component to be measured in the gas flow. The gas exchange device may in some examples be referred to, or even form part of, a ‘gas transfer unit’, ‘artificial lung’, ‘artificial lung’, or ‘oxygenator’.

[0030] By ‘sweep gas’, or ‘carrier gas’ is typically understood a gas that is passed over one side of a membrane to facilitate the exchange of gases, such as oxygen and carbon dioxide, with blood passing over the other side of the membrane. The sweep gas used in oxygenation 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 exchange sweep gas may be adjusted, for example by a gas mixer or blender, based on the 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 exchange sweep gas supplied to the fluid exchange module.

[0031] The exchange gas circuit can be described as an open circuit, wherein the fluid exchange module 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 reference sweep gas is not expelled but recirculated back through the gas exchange device.

[0032] The term ‘gas component’ refers to any individual gas that is part of a mixture of gases, such as the reference 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.

[0033] 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.

[0034] Brief Description of the Drawings

[0035] 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.

[0036] Figure 1 is a general overview of a system for transfer of one or more fluid components between blood and a fluid exchange medium.

[0037] Figure 2 shows a fluid exchange module and a gas exchange device according to an embodiment, when coupled to a circulatory system of a patient.

[0038] Figure 3 shows a system according to an embodiment, in which the fluid exchange module and the gas exchange device form separate compartments within a common gas exchange arrangement.

[0039] Figure 4 is a flow chart illustrating a method for determining a partial pressure of a gas component according to an embodiment. Figure 5 is a flow chart illustrating a method for determining a status of an oxygenator according to an embodiment.

[0040] 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.

[0041] Detailed Description

[0042] Figure 1 shows by way of example a system 100 for exchanging one or more fluid components with blood in a circulatory system of a patient 10. The system 100 comprises a fluid exchange module 110 for transferring fluid components between the blood and a fluid exchange medium, wherein the blood is circulated in an extracorporeal circuit 105 and the fluid exchange medium is passed through the fluid exchange module 110.

[0043] Examples of fluid exchange modules 110 as disclosed herein include devices for exchange of blood gases, as cardiopulmonary bypass machines (heart-lung machines) providing circulatory and respiratory support in the operating theatre while the heart is stopped for surgery, extracorporeal membrane oxygenator (ECMO) devices providing circulatory and respiratory support in intensive care units, and extracorporeal carbon dioxide removal (ECCO2R) devices removing excess carbon dioxide from the blood. Further examples include dialysis devices for exchange of liquid components, such as haemolysis machines and continuous renal replacement therapy (CRRT) machines.

[0044] The fluid exchange module 110 is configured to facilitate exchange of fluid components, such as gases or liquids, between the patient’s blood and a flow of fluid exchange medium passing through the fluid exchange module 110. The fluid exchange module 110 may comprise one region 114 for the fluid exchange medium and another region 116 for the blood, which are separated by a semi-permeable membrane 112.

[0045] Due to a partial pressure gradient, or a concentration difference, between individual fluid components of the fluid exchange medium and the corresponding component in the blood, this component may be passed through the membrane 112 from the fluid exchange medium into the blood region or vice versa. Several types of membranes 112 may be employed. In an example, the fluid exchange module 110 comprises a hollow fibre membrane, in which the blood flows in inside the fibres and the fluid exchange medium flows outside the fibres. Exchange of fluid components 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.

[0046] The blood in the extracorporeal circuit 105 may be circulated through the blood region 116 by a circulation unit 107, or pump. 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 comprise 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.

[0047] The subsequent sections will discuss several examples of gas exchange devices that facilitate the determination of the partial pressure of gas component in the blood passing through the fluid exchange module 110, with reference to figures 2 and 3. While these examples illustrate gas exchange devices integrated in systems comprising fluid exchange modules equipped with a gas transfer membrane for exchanging gas components between he blood and a sweep gas, it is important to recognise that the scope of the present disclosure is not limited to these configurations. The inventive concept can also be applied in conjunction with other types of fluid exchange modules, including but not limited to, those used in dialysis. Thus, the examples provided are intended to illustrate the general inventive concept and should not necessarily be construed as limiting the scope of the invention.

[0048] 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 fluid exchange module 110, in this example comprising a gas transfer membrane 112 to facilitate exchange of blood gases with a fluid exchange medium being an exchange sweep gas. More specifically, the depicted fluid exchange module 110 may be referred to as an oxygenator 110, arranged to oxygenate venous blood and remove carbon dioxide as the blood passes through the extracorporeal circuit.

[0049] The oxygenator 110 is connected to an exchange gas circuit 160 for supply of the exchange sweep gas. A gas blender 162 may be connected to the exchange gas circuit 160 to control the flow of exchange sweep gas to the oxygenator 110. Typically, the gas blender 162 comprises a plurality of inlets configured to receive medical gas Pl, P2, P3 from a respective gas source (not shown). Medical oxygen may be supplied to the gas blender 162 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. The gases may be mixed into a sweep gas mixture by the gas blender 162 and supplied to the oxygenator 110 via a tubing. The composition and flow rate of the exchange sweep gas may be adjusted according to the patient’s needs, allowing healthcare professionals to control the oxygen levels delivered to the patient. The gas blender 162 may be electronically controlled, and in some examples configured to utilise sensor input to achieve the accurate gas composition and flow rate.

[0050] During operation, gas components such as oxygen and carbon dioxide may pass through the membrane 112 of the oxygenator 110 such that venous blood supplied to the oxygenator 110 is oxygenated into arterial blood that can be fed back to the patient 10. Other gas components like anaesthetic gases present in the sweep gas or the blood may flow across the membrane as well. The used exchange sweep gas may leave the oxygenator 110 and be expelled to the ambient atmosphere or taken care of otherwise, such as through a gas discharge system. The exchange gas circuit 160 may hence be referred to as an open circuit, allowing the oxygenator 110 to be provided with a continuous flow of fresh exchange sweep gas which is discharged after use.

[0051] The system 100 shown in figure 2 may further comprise a gas exchange device 120, which is coupled to the extracorporeal circuit at a position downstream of the fluid exchange module 110 to allow the partial pressures of gas components in the blood to be determined. The gas exchange device 120 may operate in a similar manner as the oxygenator 110, comprising a gas transfer membrane 122 arranged to allow blood gases to be exchanged between the blood and a flow of a reference sweep gas. By recirculating the reference sweep gas through the gas exchange device 120, the reference sweep gas may equilibrate with the gas components in the blood. The concentrations or partial pressures of the gas components in the reference sweep gas may then be used as a measure of the partial pressures of the gas components in the blood.

[0052] The reference gas circuit 130 may hence, in contrast to the exchange gas circuit 160, be operated as a closed circuit in which substantially the same gas is recirculated throughout the measurements. The reference sweep gas may, for example, be of the same type and composition as the exchange sweep gas, or of another composition, including air. In some examples, the reference gas circuit 130 may be initially provided with gas from the gas blender 162 which is then recirculated to enable the gas component measurements.

[0053] The concentrations or partial pressures of the gas components in the recirculated reference sweep gas may be measured by means of a sensor unit 140 coupled to the reference gas circuit 130. The sensor unit 140 is coupled in series with the gas exchange device 120 and configured to generate data indicating the concentration or partial pressure of one or more gas components in the recirculated reference sweep gas. The sensor unit 140 in the example of figure 2 comprises an oxygen sensor 142 arranged to interact with the reference sweep gas flow to measure the oxygen concentration or oxygen partial pressure. Examples of oxygen sensors 142 include electrochemical sensors and optical sensors. Furthermore, the sensor unit 140 comprises a carbon dioxide sensor 144 arranged to measure the carbon dioxide concentration in the reference 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 reference sweep gas.

[0054] The sensors 142, 144 may be components of a gas analyser device, which can either be a standalone unit connected to the reference gas circuit 130 via tubing or integrated directly within the gas exchange device 120. In alternative configurations, one or more of these sensors 142, 144 may be deployed as independent units linked to the reference gas circuit 130. A pump 146 may be provided for recirculating the reference sweep gas in the closed circuit formed by the reference gas circuit 130. Examples of pumps include diaphragm pumps and piston pumps. In the present example, the pump 146 is integrated in the sensor unit 140, or gas analyser. However, in alternative configurations, the pump 146 may be a standalone unit coupled to the reference gas circuit 130.

[0055] The sensors 142, 144 are communicatively coupled to a control unit 180 for processing of the sensor data generated by the sensors 142, 144. The control unit 180 may be incorporated in the sensor unit 140 or the gas exchange device 120, or arranged at another location, physically separate from the sensor unit 140 and the gas exchange device 120. Further, the control unit 180 may be arranged to control the operation of the gas blender 162. Feedback from the sensor unit 140, which measures the partial pressures or concentrations of gases like oxygen and carbon dioxide in the recirculated reference 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 162 to the gas exchange device 120. For instance, if the sensor data indicates a deficiency in oxygen level in the blood, the control unit 180 can instruct the gas blender 142 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.

[0056] In some examples, a valve arrangement (not shown) may be provided to switch the gas exchange device 120 from the reference gas circuit 130 to the exchange gas circuit 160. More specifically, the gas exchange device 120 may be coupled to the open circuit supplying the oxygenator 110 with the fresh exchange sweep gas. This allows the gas exchange device 120 to be operated as an oxygenator, contributing to the oxygenation provided by the oxygenator 110. By switching the gas exchange device 120 between the two circuits, i.e., the gas exchange circuit and the reference gas circuit, the gas exchange device 120 may alternatingly be used for oxygenation and measurement purposes. In one example, the gas exchange device 120 may be switched from a measurement mode to an oxygenation mode in case the gas transfer capacity of the oxygenator 120 is sinking below a predetermined threshold due to, e.g., accumulation of blood clots or deposition of a layer increasing diffusion resistance of the membrane 112.

[0057] An alternative configuration of the gas exchange device 120 is shown in figure 3, where the fluid exchange module and the gas exchange device form separate compartments within a common gas exchange arrangement 150. The gas exchange module and the gas exchange device may be configured similarly to the ones in figure 2, with gas transfer membranes facilitating gas exchange between the blood and a gas flow. However, in the present configuration, two (or more) flow paths are defined through the gas exchange arrangement 150: a main flow path for the ‘normal’ operation, i.e., the oxygenation of the blood (corresponding to the operation of the fluid exchange module 110 described with reference to figure 2), and a secondary flow path for the measurements of the gas components (corresponding to the operation of the gas exchange device in figure 2). The first flow path may be defined by a first compartment 151 and the second flow path by a second compartment 152 of the gas exchange arrangement 150. The gas flows supplied to the respective flow paths may be controlled by a valve arrangement 170, as will be described in the following.

[0058] The gas exchange arrangement 150 may comprise a blood inlet 153 and a blood outlet 154 for guiding the blood of the extracorporeal circuit through both compartments 151, 152. As shown in figure 3, the first compartment 151 and the second compartment 152 may be arranged in series with respect to the flow of blood, such that the blood first passes through the first compartment 151 and thereafter the second compartment 152 on its way between the blood inlet 153 and the blood outlet 154. The first compartment 153, in which the blood is oxygenated by fresh sweep gas, may be larger than the second compartment 154.

[0059] The exchange sweep gas may be guided through the first compartment 151, i.e., along the main flow path, by means of a first gas inlet 155 and a first gas outlet 156. In the depicted example, the flow path between the first gas inlet 155 and the first gas outlet 156 is substantially orthogonal to the blood’s flow path between the blood inlet 153 and the blood outlet 154. Similarly, the reference sweep gas may be guided through the second compartment 152, i.e., along the secondary flow path, by means of a second gas inlet 157 and a second gas outlet 158. The secondary flow path may typically be parallel to the main flow path and orthogonal to the blood’s flow path. It will however be appreciated that other configurations and orientations may be possible, as long as the blood may pass through both compartments 151, 152 and interact both with the main flow of sweep gas for oxygenation and the secondary flow of sweep gas for measurement purposes.

[0060] The membrane 112 may be a fibre membrane comprising a plurality of hollow fibres, configured to allow the gas transfer to occur through the walls of the fibres. In one example, the blood may flow inside the fibres and the sweep gas (i.e., the exchange sweep gas and the reference sweep gas) outside the fibres. The fibres may extend in parallel along the flow path of the blood, between the blood inlet 153 and the blood outlet 154.

[0061] The sweep gas compartments 151, 152 may be separated from each other by a wall 159. The wall 159 may be gas tight so keep the respective gas flows separate, and may further be arranged such that the second compartment 152, for the reference sweep gas, is as small as possible so as to not significantly interfere with the overall gas exchange capacity of the gas exchange arrangement 150.

[0062] The first compartment 151 may hence be part of an exchange gas circuit for providing fresh sweep gas for the gas transfer process, whereas the second compartment 152 may be part of a reference gas circuit 130 for circulating the sweep gas to allow it to equilibrate with the blood gases. The concentration or partial pressure of various gas components in the reference sweep gas, such as oxygen, carbon dioxide, and anaesthetic agent, may be measured by a sensor unit 140 coupled to the reference gas circuit 130 as mentioned above.

[0063] The valve arrangement 170 may be configured to selectively couple the gas exchange 110 device to the exchange gas circuit and the reference gas circuit 130. The valve arrangement 170 may comprise a first valve arranged upstream of the gas exchange arrangement 150 to control the flow of sweep gas supplied to the second compartment 152, and a second valve arranged downstream of the gas exchange arrangement 150 to control the flow of sweep gas leaving the second compartment 152. Each of the valves may be of a two-way valve type, which can switch between opening to one circuit while closing off the other. The first valve allows the second gas inlet 157 to either be connected to the supply of fresh sweep gas or to the sweep gas circulating in the reference gas circuit 130. Similarly, the second valve may be operable to either exhaust the used sweep gas from the system or direct it back towards the second gas inlet 157 for recirculation through the second compartment 152. The valve arrangement 170 allows for the gas exchange device 110 to be operated in two different modes: a measurement mode, or recirculation mode, in which the valve arrangement 170 directs the flow of reference sweep gas through the reference gas circuit 130, and an oxygenation mode in which the valve arrangement 170 opens the second compartment 152 to fresh sweep gas.

[0064] The valve arrangement 170 allows the gas exchange device to operate in two distinct modes, i.e., the oxygenation mode and the measurement mode. When not engaged in measurement activities, the device may be switched to the oxygenation mode, where it may contribute to the oxygenation of the blood. This dual-mode functionality allows for efficient utilisation of the device, ensuring continuous and efficient oxygenation.

[0065] Alternatively, the gas exchange device is arranged permanently in the measurement mode to allow continuous monitoring of the blood gas content. This mode may be maintained until there is a need for an additional ‘boost’ in oxygenation efficiency, for example in case there is a reduced gas transfer capacity of the fluid exchange module. The gas transfer capacity of the membrane 112 may 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 112. By engaging the second compartment 152 in the oxygenation process, a temporary increase in gas transfer capacity may be achieved.

[0066] The valve arrangement 170 may be controlled by the control unit 180. The control unit 180 may, for example, be configured to switch the gas exchange device 120 back to the oxygenation mode after the blood gas measurements have been finished. This allows the gas exchange unit 120 to take part in the oxygenation process performed by the oxygenator part of the gas exchange arrangement 150. As previously mentioned, the control unit 180 may also be arranged to control the operation of the gas blender controlling the composition and flow rate of exchange sweep gas.

[0067] 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 4. The method may be performed in a system 100 configured similarly to the ones disclosed in figures 2 and 3. According to figure 4, blood and exchange medium are passed SI 10 through the fluid exchange module 110 to allow fluid transfer to take place across the membrane of the fluid exchange module 110. This may for example be part of an oxygenation process or a dialysis process. The method further comprises passing S120 the blood and a reference sweep gas through a gas exchange device 120 to transfer one or more gas components between the blood and the reference sweep gas. The gas exchange device 120 may be a separate unit, utilised in conjunction with e.g. an oxygenator or a dialysis apparatus. In case of an oxygenator 110, the gas exchange device 120 may also be integrated with the oxygenator 110 as shown in figure 3. The gas exchange device 120 may be supplied with the reference sweep gas from a reference gas circuit 130, or from an exchange gas circuit which also provides the oxygenator 110 with sweep gas.

[0068] The gas exchange device 120 may be operated in a measurement mode, where the reference sweep gas is recirculated S130 in the exchange gas circuit 130. Gas exchange occurs across the membrane 112 in a manner similar to the oxygenator 110. However, a difference is that the sweep gas is not replenished. Over time, this leads to a gradual decrease in the concentration differences or partial pressure differences between the gas components in the 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. The partial pressures of the gas components in the blood may then be determined S140 by measuring the concentration or partial pressure of the gas components in the recirculating reference sweep gas.

[0069] The transient phase of the measurement mode may be utilised to gather information about the system. One example is depicted in figure 5, which is allow chart outlining a method for determining a status of a system similar to the one shown in figure 3, i.e., with the oxygenator 110 and the gas exchange device 120 integrated into the same unit. Figure 5 shows a method wherein blood is passed S210 through the first and second compartments 151, 152 of the gas exchange arrangement 150, and wherein sweep gas is passed S220 through two separate compartments 151, 152 of the same. In this state, both compartments 151, 152 are supplied with the same flow of sweep gas passing S220 through the gas exchange arrangement 150 through two separate, parallel flow paths - a main flow path through the first compartment 151 and a secondary, smaller flow path through the second compartment 152.

[0070] In another step, the path of sweep gas through the second compartment 152 is switched into a closed circuit, in which the gas is recirculating through the second compartment. The concentration or partial pressure of the gas component in the recirculating gas may be monitored S240 during the initial, transient phase of the measurement mode. The rate of the change can be analysed to identify when the system reaches equilibrium, i.e., when the partial pressures of the gas components in the blood have equilibrated with the partial pressures of the blood gases in the recirculating sweep gas. 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.

[0071] By determining S250 the time constant, it 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.

[0072] 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.

[0073] Moreover, the rate at which the equilibrium is approached (as evidenced by the time constant) may help determining S260 the status of the gas exchange device 110 and the common gas exchange arrangement 150. 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. 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.

[0074] 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

[0075] The control unit 180 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 figures 3-4 and described above. Generally, the control unit 180 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

22CLAIMS1. A system (100) comprising: a fluid exchange module (110) configured to be coupled to an extracorporeal circuit (105), circulating blood of a circulatory system of a patient, to transfer a fluid component between the blood and an exchange medium flowing through the fluid exchange module; a gas exchange device (120) configured to be coupled to the extracorporeal circuit to transfer a gas component between the blood and a reference sweep gas passing through the gas exchange device; a reference gas circuit (130) configured to be operated as a closed circuit recirculating the reference sweep gas through the gas exchange device; and a sensor unit (140) 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 reference sweep gas; wherein the fluid exchange module and the gas exchange device form separate compartments (151, 152) within a common gas exchange arrangement (150).

2. The system according to claim 1, wherein the fluid exchange module comprises a dialysis membrane and wherein the exchange medium is a dialysate.

3. The system according to claim 1, wherein the fluid exchange module comprises a gas transfer membrane and wherein the exchange medium is an exchange sweep gas.

4. The system according to claim 3, wherein the gas transfer membrane comprises a plurality of hollow fibres.

5. The system according to claim 4, wherein the fluid exchange module is configured to pass the blood through the plurality of hollow fibres and to pass the exchange medium outside the plurality of hollow fibres.

6. The system according to claim 4, wherein the fluid exchange module is configured to pass the exchange medium through the plurality of hollow fibres and to pass the blood outside the plurality of hollow fibres.

7. The system according to any of the preceding claims, wherein the common gas exchange arrangement comprises: a blood inlet (153) and a blood outlet (154) for guiding the blood through the compartments; a first gas inlet (155) and a first gas outlet (156) for guiding the exchange sweep gas through the fluid exchange module; and a second gas inlet (157) and a second gas outlet (158) for guiding the reference sweep gas through the gas exchange device.

8. The system according to any of the preceding claims, further comprising: an exchange gas circuit (160) configured to be operated as an open circuit providing the exchange sweep gas to the fluid exchange module from a gas supply; and a valve arrangement (170) configured to selectively couple the gas exchange device to the exchange gas circuit and the reference gas circuit.

9. The system according to any of the preceding claims, wherein the sensor unit comprises a pump for circulating the reference sweep gas in the closed circuit.

10. The system according to any of the preceding claims, wherein a flow rate of the reference sweep gas is smaller than a flow rate of the exchange medium.

11. A method for determining a partial pressure of a gas component in blood in a circulatory system of a patient, comprising: passing (SI 10) the blood and an exchange medium through a fluid exchange module device to transfer a fluid component between the blood and the exchange medium;passing (S 120) the blood and a reference sweep gas flow through a gas exchange device to transfer the gas component between the blood and the reference sweep gas flow; recirculating (SI 30) the reference sweep gas flow, passing through the gas exchange device, in a closed circuit comprising a sensor unit generating a sensor signal indicating a concentration or partial pressure of the gas component in the reference sweep gas flow; and determining (SI 40) the partial pressure of the gas component in the blood based on the sensor signal.

12. The method according to claim 11, wherein the fluid exchange module comprises a dialysis membrane and wherein the exchange medium is a dialysate.

13. The method according to claim 11, wherein the fluid exchange module comprises a gas transfer membrane, the exchange medium is an exchange sweep gas, and the fluid component is the gas component, the method comprising: operating the gas exchange device in a standard operation mode in which the gas exchange device is coupled to a flow of the exchange sweep gas; operating the gas exchange device in a measurement mode in which the gas exchange device is coupled to the reference gas flow; and selectively switching the gas exchange device between the standard operation mode and the measurement mode.

14. The method according to claim 13, comprising: monitoring a change in the concentration or partial pressure of the gas component in the reference sweep gas during an initial phase of the measurement mode; determining a time constant associated with the change; and determining a status of the fluid exchange module based on the time constant.

15. The method according to claim 13, wherein the gas component is one or more of oxygen, carbon dioxide, and an anaesthetic agent.2516. The method according to any of claims 11-15, comprising: passing the blood through a plurality of hollow fibres of a hollow-fibre membrane; and passing the exchange medium outside the plurality of hollow fibres.

17. The method according to any of claims 11-15, comprising: passing the exchange medium through a plurality of hollow fibres of a hollowfibre membrane; and passing the blood outside the plurality of hollow fibres.

18. The method according to any of claims 11-17, wherein a flow rate of the reference sweep gas is smaller than a flow rate of the exchange medium.

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