Determination of exhaust gas flow rate of blood oxygenators

Abstract

A method (200) for determining the total flow rate of exhaust gas exiting a gas exchange device (110) coupled to the circulatory system of a patient (10) is disclosed. The gas exchange device is configured to provide oxygen-rich blood to the circulatory system by exposing oxygen-deficient blood to oxygen provided by an incoming gas and to allow the passage of excess oxygen into the exhaust gas. The method involves the step of determining the total flow rate of exhaust gas from the concentration and flow rate of oxygen leaving the gas exchange device. The concentration is recovered from a sensor, while the flow rate is determined based on a mass equilibrium approach, and the amount of oxygen leaving the gas exchange device corresponds to the difference between the amount of oxygen supplied to the gas exchange device and the amount of oxygen absorbed by the blood during gas exchange.

Description

Technology Field

[0001] The present disclosure relates to a method and system for gas exchange in a patient's circulatory system using a gas exchange device. More specifically, the present disclosure relates to a technique for determining the flow rate of exhaust gas exiting such a gas exchange device. Background Technology

[0002] Gas exchange in the blood is a physical process in which gases move through membranes, such as the blood-air barrier of the alveoli in mammalian lungs, allowing oxygen to be absorbed by the blood and carbon dioxide to be released from the blood.

[0003] In cases of respiratory failure or bypass, an external gas exchange device may be used to support or replace the patient's lung function. Gas exchange devices typically use sweep gas to supply oxygen to the blood and remove carbon dioxide from the blood.

[0004] The performance of gas exchange devices is critical for patient safety and efficient medical treatment. Too slow absorption of oxygen or too slow emission of carbon dioxide can rapidly lead to dangerous situations that jeopardize patient health and safety. Therefore, thorough monitoring of the composition and flow rate of the sweep gas is desirable.

[0005] A commonly monitored work parameter is oxygen uptake in the blood, which can be estimated by the difference between the oxygen content of the incoming sweep gas and the outgoing sweep gas—that is, the oxygen content before and after gas exchange occurs. This estimation typically requires knowing the total flow rate and oxygen concentration of the sweep gas.

[0006] While inflow rates can be measured directly using appropriate measuring devices, determining outflow rates with high accuracy is more difficult. Direct flow rate measurement at the outlet of a gas exchange device carries the risk of leakage losses, such as when sweep gas escapes through emergency outlets commonly implemented in gas exchange devices with high volumes. Furthermore, outflow sweep gas tends to become saturated with water vapor, and this condensation can limit the accuracy of flow rate measurements. The problem to be solved

[0007] Therefore, there is a need for improved and alternative technologies to monitor the flow rate of gas passing through gas exchange devices, and in particular to determine the total flow rate of exhaust gas exiting such gas exchange devices. means of solving the problem

[0008] In light of the preceding task, the present disclosure provides an improved or alternative technology having the characteristics set forth in the independent claim.

[0009] Therefore, according to a first aspect, a method for determining the total flow rate of exhaust gas exiting a gas exchange device coupled to the circulatory system of a patient is provided, wherein the gas exchange device is configured to provide oxygen-rich blood to the circulatory system by exposing the patient's oxygen-deficient blood to oxygen provided by the incoming gas, and to allow the passage of excess oxygen into the exhaust gas. The method is:

[0010] A step of receiving sensor data indicating the oxygen content in oxygen-rich blood and the oxygen content in oxygen-deficient blood;

[0011] A step of determining oxygen uptake in blood based at least partially on the blood flow rate through a gas exchange device and the difference between the oxygen content in oxygen-rich blood and the oxygen content in oxygen-deficient blood;

[0012] A step of determining the flow rate of oxygen in the incoming gas based at least partially on the oxygen concentration in the incoming gas and the total flow rate of the incoming gas;

[0013] A step of determining the flow rate of oxygen in the exhaust gas based at least partially on the difference between the flow rate of oxygen in the incoming gas and the oxygen absorption rate in the blood;

[0014] A step of receiving sensor data indicating the oxygen concentration in the exhaust gas; and

[0015] It includes a step of determining the total flow rate of the exhaust gas based at least partially on the flow rate of oxygen in the exhaust gas and the oxygen concentration in the exhaust gas.

[0016] In a second aspect, a system for exchanging blood with one or more gases in a patient's circulatory system is provided. The system comprises a gas exchange device having a gas inlet for receiving an incoming gas and an outlet for releasing an exhaust gas, wherein the gas exchange device is configured to provide oxygen-rich blood by exposing the patient's oxygen-deficient blood to oxygen provided by the incoming gas and to allow the passage of excess oxygen into the exhaust gas. The system also comprises a sensor device configured to generate sensor data indicating the oxygen content in the oxygen-rich blood, the oxygen content in the oxygen-deficient blood, and the oxygen concentration in the exhaust gas. Furthermore, the system comprises one or more processors and one or more non-transient computer-readable media storing instructions executable by the one or more processors, wherein, when the instructions are executed, the system

[0017] An operation to determine the degree of oxygen absorption in blood based at least partially on the blood flow rate through a gas exchange device and the difference between the oxygen content in oxygen-rich blood and the oxygen content in oxygen-deficient blood;

[0018] An operation to determine the flow rate of oxygen in an incoming gas based at least partially on the oxygen concentration in the incoming gas and the total flow rate of the incoming gas;

[0019] The operation of determining the flow rate of oxygen in the exhaust gas based at least partially on the difference between the flow rate of oxygen in the incoming gas and the oxygen absorption rate in the blood; and

[0020] An operation including determining the total flow rate of exhaust gas based at least partially on the flow rate of oxygen in the exhaust gas and the oxygen concentration in the exhaust gas is performed.

[0021] In these aspects, the total flow rate of the exhaust gas is obtained from the concentration and flow rate of oxygen leaving the gas exchange device. While the concentration may be recovered from a sensor, the flow rate is determined based on a mass equilibrium approach, and the amount of oxygen leaving the gas exchange device corresponds to the difference between the amount of oxygen supplied to the gas exchange device and the amount of oxygen absorbed by the blood during gas exchange. The amount of oxygen absorbed by the blood may also be determined based on blood sensor data by comparing the oxygen content in oxygen-rich blood with the oxygen content in oxygen-deficient blood. By subtracting the amount of oxygen absorbed by the blood from the amount of oxygen supplied to the gas exchange device, the amount of oxygen remaining in the sweep gas after gas exchange can be determined. By combining the amount of oxygen in the exhaust gas with the concentration of oxygen in the exhaust gas, the total flow rate of the exhaust gas can be determined without directly measuring the flow rate, for example, using a flow meter.

[0022] Direct measurement of the total flow rate of exhaust gas may be difficult for several reasons. First, exhaust gas may be saturated with water vapor and may have an elevated temperature corresponding to or close to the patient's body temperature. This is associated with a significant risk of water vapor condensation, which can reduce the accuracy of flow rate measurements as the condensed water may interfere with sensor readings, block the sensor's path, and effectively alter the relative concentration of other gases, including oxygen. Second, many gas exchange devices are equipped with an additional gas outlet for patient safety reasons, and this additional outlet is often positioned in a constant open state to allow a portion of the exhaust gas flow to pass through. The additional outlet forms an emergency outlet that prevents overpressure from building up in the gas exchange device if the primary outlet becomes blocked for any reason. Since a portion of the exhaust gas may escape through the emergency outlet instead of the primary outlet, there is a risk that the flow sensor placed at the primary outlet will provide an inaccurate measurement of the total exhaust gas flow rate. Approximating the total exhaust gas flow rate based on the incoming gas flow rate carries a particular risk of inaccuracy for gas exchange devices with leaks, such as those through emergency outlets.

[0023] This aspect therefore provides an alternative to the method in which the total flow rate of exhaust gas is determined by direct flow rate measurement or approximated by the flow rate of incoming gas.

[0024] In the context of this disclosure, the terms “flow” or “flow rate” typically refer to how gas moves through a system. Flow rate may refer to the total flow rate of gas supplied to or exhausted by a gas exchange device, or the flow rate of a specific component of gas, such as oxygen or carbon dioxide. Flow rate may generally be understood as a term describing the amount of gas moving through a given cross-sectional area per unit time, and may be measured in volume or mass. A flow rate measured in volume may be referred to as volumetric flow rate, describing how much volume of gas passes through a given area at a specific time. In SI systems, volumetric flow rate is often cubic meters per second (m³). 3 It is expressed as / s). However, in this context, flow rate may also commonly be expressed in liters per minute (L / min). Accordingly, volumetric flow rate typically describes how many liters of gas, such as oxygen, are supplied to (or exhausted by) a gas exchange device per minute. Alternatively, flow rate may be measured as mass flow rate, which describes the mass of gas (such as oxygen) passing through a given area at a specific time. Mass flow rate may, accordingly, be expressed in kilograms per second (kg / s). Mass flow rate may be particularly useful when the density of the gas may vary under variable conditions, as it can provide a measurement independent of temperature, pressure, and moisture content. You will understand that volumetric flow rate is proportional to mass flow rate, and that volumetric flow rate can therefore be converted to mass flow rate (and vice versa) for a given temperature and pressure of the gas.

[0025] Standard Cubic Centimetre per Minute (SCCM) is an example of a unit that can be used to quantify the flow rate of a fluid and can be understood as the mass flow rate of one cubic centimeter per minute of gas at a density specified under certain standard conditions for temperature and pressure. Standard conditions may vary between different regulatory bodies, but may correspond, for example, to a temperature of 0°C and a pressure of 1.01 bar.

[0026] Oxygen content in blood typically refers to the total concentration of oxygen transported by the blood flow. Oxygen generally exists in the blood in two main forms: bound to hemoglobin and dissolved directly in the plasma. While other forms may exist, it should be understood that these two forms tend to account for the majority of the oxygen content. In common, the majority of oxygen transported in the blood is bound to hemoglobin, while a smaller portion of oxygen in the blood is dissolved in the plasma. Therefore, oxygen content typically refers to the total concentration of oxygen transported by hemoglobin and plasma. Oxygen content may also be expressed as the volume of oxygen per unit volume of blood (such as millimeters of oxygen per deciliter of blood) or the amount of oxygen per unit volume of blood (such as millimoles of oxygen per deciliter of blood).

[0027] The oxygen concentrations of the incoming and outgoing gases may typically be measured as a percentage of the total gas mixture. For example, medical oxygen supplied to a gas exchange device may have a concentration of approximately 21% (corresponding to the concentration in air) to 100%, depending on clinical need. Percentages are typically described as volumetric ratios, such as liters of oxygen per liter of total gas. However, in some examples, the concentration may also be expressed as a molar ratio (the number of moles of oxygen per mole of the gas mixture) or as the amount of oxygen substance per unit volume of the gas mixture.

[0028] Oxygen-deficient blood typically refers to blood circulating through the human body that delivers oxygen to tissues. Consequently, it may have a higher concentration of carbon dioxide. Oxygen-deficient blood may also be referred to as deoxygenated blood or venous blood. Oxygen-deficient blood may be supplied to a gas exchange device to enrich it with oxygen.

[0029] Oxygen-rich blood, also referred to as oxygenated blood or arterial blood, is understood as blood that has been enriched with oxygen by a gas exchange device. Oxygen-rich blood may be returned to the patient's body to supply oxygen to the tissues.

[0030] As previously mentioned, the oxygen content in blood may refer to the total concentration of oxygen carried by the blood flow, including both oxygen bound to hemoglobin and oxygen dissolved in the plasma. Accordingly, sensor data may represent both: the concentration of oxygen bound to hemoglobin in oxygen-rich blood and oxygen-deficient blood, and the concentration of oxygen dissolved in the blood plasma in oxygen-rich blood and oxygen-deficient blood. By considering both the concentration of oxygen bound to hemoglobin and the concentration of oxygen dissolved in the plasma, the total concentration or amount of oxygen absorbed by the blood during gas exchange can be determined with relatively high accuracy.

[0031] Alternatively or additionally, for oxygen-deficient blood—that is, blood not sufficiently saturated with oxygen—the concentration of oxygen bound to hemoglobin may be determined based on the concentration of oxygen dissolved in plasma. This is based on establishing a known relationship between the concentration of oxygen dissolved in plasma (also referred to as the partial pressure of oxygen) and the concentration of oxygen bound to hemoglobin (also referred to as the oxygen saturation of hemoglobin). Accordingly, by measuring the partial pressure of oxygen in oxygen-deficient blood, this relationship may be used to estimate oxygen saturation without directly measuring the oxygen saturation level.

[0032] Several sensors may be used to measure oxygen concentration in exhaust gases. However, the concentration of water vapor in exhaust gases has been observed to present difficulties, as it may interfere with the sensors and affect the relative concentrations of other gases containing oxygen. In some cases, this may be resolved by reducing the temperature of the exhaust gas to allow water vapor to condense in a more controlled manner before the sensor is exposed to the gas. The exhaust gas may be cooled to ambient room temperature or even lower to further reduce the humidity of the exhaust gas. In additional examples, the sensor may be heated directly (directly on the sensor chip or adjacent to the sensor chip) or indirectly (the entire sensor assembly / tube) to reduce the risk of condensed water interfering with the sensor's operation. Additionally, or alternatively, the exhaust gas may be passed through a device to allow water vapor to be removed from the gas. An example of such a device is the Nafion tube, which will be described in more detail with reference to FIG. 1. A combination is also possible in which the exhaust gas is cooled and the heated sensor further reduces the risk of condensation.

[0033] A sensor for measuring the oxygen concentration of the exhaust gas may be integrated into the gas exchange device, that is, it may be installed, for example, permanently or replaceably at the outlet of the gas exchange device. However, in other examples, the sensor may be a separate unit configured to measure the exhaust gas downstream of the gas exchange device.

[0034] In some cases, the flow rate of carbon dioxide in the exhaust gas may be determined based on sensor data indicating the total flow rate of the exhaust gas and the concentration of carbon dioxide in the exhaust gas. The flow rate of carbon dioxide may be used as an indicator of the performance of the gas exchange device and, more specifically, the efficiency with which gas exchange is performed. A relatively low or decreasing concentration or flow rate of carbon dioxide in the exhaust gas may indicate that the membrane of the gas exchange device, where gas exchange between the sweep gas and blood occurs, is operating at reduced performance. Common causes may include membrane clogging or blockage and deposition on the membrane fibers, which may increase diffusion resistance and reduce gas exchange efficiency. Therefore, the condition of the gas exchange device may be determined by comparing the concentration or flow rate of carbon dioxide in the exhaust gas with a threshold measurement. If the concentration or flow rate of carbon dioxide meets or exceeds the threshold measurement, the gas exchange device may be determined to be operating as intended. If the concentration or flow rate of carbon dioxide is lower than the threshold measurement, a warning or signal may be issued indicating that the gas exchange device needs to be replaced. The threshold measurement may be a predetermined reference value based on the operating point of the gas exchange device, which is defined by, for example, the inflow rate of the sweep gas, the flow rate of blood through the gas exchange device, and the amount of carbon dioxide dissolved in the blood.

[0035] In the preceding example, while some parameters for determining the total flow rate of the exhaust gas may be known or predetermined from the system settings, other parameters may be recovered from sensor data. The flow of blood through the gas exchange device—that is, the flow rate of blood where gas exchange may occur—may be measured by an ultrasonic flow sensor, or it may be a known parameter determined by the system settings, such as the pump rate of the pump used to circulate blood through the system. Furthermore, the oxygen concentration in the incoming gas and the total flow rate of the incoming gas may be known from the settings of an incoming gas supplier, such as a gas blender used to supply the sweep gas required by the gas exchange device. However, the oxygen content in oxygen-rich and oxygen-deficient blood, and the oxygen concentration in the exhaust gas, may also be recovered from sensor data.

[0036] The second aspect may generally have the same characteristics and advantages as the first aspect. It should be further noted that the present disclosure relates to all possible combinations of characteristics unless otherwise expressly stated. Brief explanation of the drawing

[0037] The prior and additional purposes, features, and advantages of the present disclosure will be better understood through the following exemplary and non-limiting detailed description of examples of the present disclosure with reference to the accompanying drawings, in which the same reference numerals will be used for similar elements. FIG. 1 is a drawing illustrating a system according to an example, comprising a gas exchange device coupled to an extracorporeal circulation unit. Figure 2 is a diagram illustrating an example of a method for determining the total flow rate of exhaust gas emitted by a gas exchange device. As illustrated in the drawings, the sizes of elements and properties may be exaggerated for illustrative purposes and are thus provided to illustrate the general structure of the example. Similar reference numbers refer to similar elements throughout. Specific details for implementing the invention

[0038] FIG. 1 illustrates, by way of example, a system (100) for exchanging blood with one or more gases in the circulatory system of a patient (10). The system (100) includes a gas exchange device (110) configured to provide oxygen-rich blood by exposing the oxygen-deficient blood of the patient (10) to oxygen provided by an incoming gas and to allow the passage of excess oxygen into the exhaust gas. The system further includes sensor devices (122, 123, 124) configured to generate sensor data indicating the oxygen content in the oxygen-rich blood, the oxygen content in the oxygen-deficient blood, and the oxygen content in the exhaust gas. The sensor data may be processed by a processor (140) configured to determine the total flow rate of the exhaust gas based on the sensor data, as described in more detail in conjunction with FIG. 2.

[0039] Examples of systems (100) according to the present disclosure include cardiopulmonary bypass machines (cardiopulmonary machines) that provide circulatory and respiratory support in an operating room while the heart is stopped for surgery, extracorporeal membrane oxygenation (ECMO) devices that provide circulatory and respiratory support in an intensive care unit, and extracorporeal carbon dioxide removal (ECCO2R) devices that remove excess carbon dioxide from the blood.

[0040] In the present example, a gas exchange device (110) is placed in an extracorporeal circulation unit (105), where the patient's blood is circulated through the gas exchange device (110) by a circulation unit (107). The extracorporeal circulation unit (105) includes a conventional fluid line or circuit tubing for connecting various components of the extracorporeal circulation unit and transporting the patient's blood through the gas exchange device (110).

[0041] The circulation unit (107) may include a roller pump or a centrifugal pump, for example, depending on the specific type of system (100). A roller pump typically includes a rotating roller that compresses a flexible tube or membrane. As the roller rotates, it squeezes the tube to create a pulsating flow of blood. On the other hand, a centrifugal pump uses a rapidly rotating impeller to generate centrifugal force, which pushes the blood outward to create a substantially continuous flow of blood. Centrifugal pumps have been observed to reduce the risk of hemolysis, i.e., the destruction of red blood cells, and to improve patient comfort.

[0042] The gas exchange device (110) is configured to facilitate gas exchange between the patient's blood and sweep gas passing through the gas exchange device (110). Typically, the gas exchange device is configured to allow oxygen to pass from the sweep gas to the blood to supply oxygen to the blood, and to allow carbon dioxide to be expelled from the blood and pass into the sweep gas. It should be understood that other types of gases and substances, including anesthetic agents and nitric oxide, may be exchanged in a similar manner.

[0043] A gas exchange device (110), which may be referred to as an oxygen supply device in some examples, may include a gas region (117) and a blood region (118) separated by a gas-permeable membrane (119). Blood may be circulated through the blood region (118) by a circulation unit (107), while sweep gas may flow through the gas region (117) through a gas inlet (112) and a gas outlet (114). At the gas inlet (112), the sweep gas may be referred to as the incoming gas, while the gas leaving the gas exchange device (110) may be referred to as the outgoing gas. Due to a partial pressure gradient or a difference in concentration between an individual component of the sweep gas and a corresponding component in the blood, this component may pass through the membrane (119) from the gas region (117) to the blood region (118) or vice versa. In particular, oxygen may pass through the membrane (119) from the gas region (117) to the blood region (118), so that oxygen-deficient blood is supplied with oxygen and becomes oxygen-rich blood. Conversely, carbon dioxide may pass through the membrane (119) from the blood region (118) to the gas region (117), so that carbon dioxide is removed from the blood flow.

[0044] Various types of membranes (119) may be used. In the example, the gas exchange device (110) comprises a hollow fiber membrane, wherein blood flows in a blood region (118) inside the fiber and a gas mixture flows in a gas region (117) outside the fiber. Oxygen and carbon dioxide exchange may also occur across the membrane formed by the walls of the hollow fiber. In the example illustrated in FIG. 1, however, the membrane (119) is schematically illustrated as a sheet.

[0045] The oxygen or carbon dioxide delivery capacity, that is, the amount of carbon dioxide or oxygen supplied to or removed from the blood flow per unit time, depends particularly on the flow rate of the blood flow, the volumetric flow of the sweep gas, the composition of the sweep gas, and the condition of the gas exchange device (110) itself. In particular, the gas delivery capacity of the membrane (119) may deteriorate over time due to the accumulation of blood clots, the deposition of a layer of increased diffusion resistance, internal water vapor condensation, and clogging of the hollow fibers of the membrane. A gas exchange device (110) that is unable to supply oxygen to the blood to a satisfactory degree may be considered to be in a deteriorated or malfunctioning state.

[0046] The incoming gas may be provided by a gas blender (130). Typically, the gas blender (130) includes a plurality of inlets (132, 134) configured to receive medical gas from each gas source (not shown). In the example illustrated in FIG. 1, the gas blender (130) includes a first inlet (132) for a medical oxygen flow (P1) and a second inlet (134) for a medical air flow (P2). However, it should be understood that more inlets may be provided, and the gas blender (130) may be used to supply other types of gas, such as nitric oxide or anesthetics.

[0047] Medical oxygen may be supplied to the gas blender (130) from an oxygen source, and the oxygen source may be an oxygen outlet of a central medical gas system of a hospital facility, a pressurized gas cylinder, or another type of oxygen source suitable for delivering oxygen for medical applications. The same applies to air, and the air may be supplied from a pressurized air outlet of a central medical gas system of a hospital facility, a pressurized cylinder, or recovered from ambient air and pressurized.

[0048] The gas received at the outlets (132, 134) may be mixed into a sweep gas mixture by a valve device (collectively represented by reference number (135)) and supplied to the gas inlet (112) of the gas exchange device (110). The valve device (135) may be configured to adjust the oxygen concentration and flow rate of the incoming gas according to the patient's needs, allowing a medical professional to control the oxygen level delivered to the patient. The valve device (135) may be electronically controlled and, in some examples, may be configured to obtain the correct gas composition and flow rate using sensor input.

[0049] The gas blender (130) may accordingly operate to deliver a specific concentration of oxygen, such as 100% oxygen, at a specific flow rate, such as 4 liters per minute. The oxygen concentration and flow rate may therefore be known or predetermined by the operation settings of the gas blender (130) and may be used as input when calculating the total flow rate of the exhaust gas, as described below. Additionally or alternatively, the mass flow rate of the gas may be determined. The mass flow rate may be determined by a mass flow sensor or by converting the volumetric flow rate into a mass flow rate. While the conversion typically requires actual conditions of known gas flow, namely temperature and pressure, the mass flow rate measurement requires information belonging to the composition of typically known gas flow. To this end, a temperature sensor, a pressure sensor, and / or a mass flow sensor (collectively indicated by reference numeral (125)) may be provided.

[0050] In the example illustrated in FIG. 1, an emergency outlet (116) is provided in the gas area (117) of the gas exchange device (110). The emergency outlet (116) forms an additional outlet, i.e., an additional "primary" outlet (114) discussed earlier, and serves to protect the gas exchange device (110) and the patient (10) from damage caused by overpressure if the primary outlet (114) is blocked or blocked. The emergency outlet (116) may be positioned in a constant-open state so that exhaust gas can freely pass through during the operation of the gas exchange device (110). Thus, the total flow of exhaust gas may be divided into partial flows: a first partial flow passing through the gas outlet (114) and a second partial flow passing through the emergency outlet (116).

[0051] The gas exchange device (110) may be positioned to discharge exhaust gas into open air, to a gas capture device, or to a gas discharge device (not shown in FIG. 1). The gas capture device or gas discharge device may be used to recycle components of the exhaust gas, for example, to prevent anesthetics and high-pressure oxygen from accumulating in the surrounding air. It should be understood that the primary discharge port (114) and the emergency discharge port (116) may be coupled to such a capture device or discharge device.

[0052] One or more sensor devices may be provided to generate sensor data indicating the oxygen content in oxygen-deficient blood, the oxygen content in oxygen-rich blood, and the oxygen content in exhaust gas. In the example illustrated in FIG. 1, a first sensor device (122) is placed at the blood outlet of the gas exchange device (110) to measure the oxygen concentration in the oxygen-rich blood leaving the gas exchange device (110). Furthermore, a second sensor device (123) is placed at the blood inlet of the gas exchange device (110) to measure the oxygen concentration in the oxygen-deficient blood supplied to the gas exchange device (110).

[0053] (In both upstream and downstream of the gas exchange device (110)) the oxygen concentration of the blood may refer to both the oxygen bound to hemoglobin and the oxygen dissolved in the plasma. The amount of oxygen bound to hemoglobin may refer to the oxygen saturation level and may be measured by an optical-based method in which the blood is illuminated and by backscattered light measured to determine the saturation level. Light at two or more separate wavelengths may be used to further increase the accuracy of the measurement of the oxygen saturation levels of oxygen-rich blood and oxygen-deficient blood, respectively.

[0054] The amount of oxygen dissolved in plasma, which may also be referred to as the partial pressure of oxygen, may be measured using a blood gas sensor, typically an electrochemical sensor such as a Clark electrode, or an optical sensor such as an optode. Electrochemical sensors typically need to come into contact with blood, such as through a gas-permeable membrane that allows oxygen to pass toward a cathode, where oxygen is electrolytically reduced. This reduction reaction generates a measurable current. The magnitude of this current is proportional to the concentration of oxygen dissolved in the blood.

[0055] Accordingly, in the example illustrated in FIG. 1, the first sensor device (122) and the second sensor device (123) each include a sensor for measuring oxygen saturation, such as a photospectral sensor, and a sensor for measuring the partial pressure of oxygen, such as a Clark electrode or an optode. However, as may already be known to those skilled in the art, other sensor configurations and technologies are also possible. Furthermore, in other examples, the oxygen saturation of hemoglobin in oxygen-rich and / or oxygen-deficient blood may be estimated based on the partial pressure of oxygen instead of being measured by a sensor. This estimation is based on the so-called oxygen dissociation curve, a known relationship describing the affinity of hemoglobin for oxygen, and how easily hemoglobin absorbs and releases oxygen dissolved in the plasma.

[0056] As illustrated in FIG. 1, the gas outlet (114) of the gas exchange device (110) may be equipped with a sensor (124) for measuring the oxygen concentration of the exhaust gas, that is, the gas released from the gas exchange device after the gas exchange process has occurred. The sensor (124) may be, for example, an electrochemical sensor that generates a current proportional to the oxygen concentration, a paramagnetic sensor that measures a change in the magnetic field caused by the presence of oxygen (due to the paramagnetic property of oxygen), or an optical sensor that measures a phase shift of modulated light caused by oxygen molecules. Other types of sensors already known to those skilled in the art are possible.

[0057] In some examples, the water vapor content in the exhaust gas may be reduced before the exhaust gas reaches the sensor (124) to measure the oxygen concentration. By removing moisture from the exhaust gas, the risk of condensation is reduced, which may now improve the accuracy of the oxygen concentration measurement. The water vapor content may be reduced by cooling the gas, for example, down to room temperature, and may cause the water vapor to condense in a more controlled manner. Additionally or alternatively, moisture may be removed by a Nafion tube (containing a sulfonated tetrafluoroethylene-based fluoropolymer copolymer), through which the exhaust gas may pass to the sensor (124). The walls of the Nafion tube may optionally be positioned to effectively "dry" the exhaust gas inside the tube, allowing water vapor to penetrate through the tube walls. In additional examples, the sensor (124) may be heated to reduce the risk of water vapor condensing on the sensor (124). The temperature of the sensor (124) may be increased, for example, by applying heat directly to the sensor chip or by applying heat to a structure adjacent to the sensor (124) and in thermal contact with it.

[0058] Each of the previously discussed sensors and sensor devices (122, 123, 124) may be an integral part of the gas exchange device (110) (and thus may be replaced together with the gas exchange device (110)), or may be a separate element that may be attached to or within the gas exchange device (110). In the latter case, the sensor(s) may be recycled. That is, they may be used with more than one gas exchange device (110).

[0059] The sensors (122, 123, 124) may be configured to communicate with the processor (140) via a wired or wireless connection, such as a local area access network (LAN).

[0060] During the operation of the system (100), oxygen-deficient blood from the extracorporeal circulation unit is supplied to the blood region (118) of the gas exchange device (110), where oxygen is supplied by sweeping gas through the gas region (117) of the gas exchange device (110). The flow rate of blood passing through the gas exchange device (110) is Q as follows. blood It is named as, and the inflow rate of the sweep gas is Q inlet Named as such, the total exhaust flow rate of the sweep gas leaving the gas exchange device (110) is Q exhaust It is named as. Blood flow rate (Q blood While ) may have a range of 2 to 6 liters per minute (L / min), the flow rate of the incoming gas (Q inlet ) and exhaust gas flow rate (Q exhaust Each typically has a range of 1 to 10 L / min.

[0061] The concentration or fraction of oxygen in the incoming gas is F in the following inlet While it is named O2, the concentration of oxygen in the exhaust gas is F exhaustIt is designated as O2. The concentration of oxygen in the sweep gas may also typically be expressed as a volumetric ratio, that is, as liters of oxygen per liter of inlet / exlet gas. Therefore, the partial gas flow of oxygen in the inlet gas (also referred to as the oxygen flow rate) is F inlet O2·Q inlet It is expressed as, and the flow rate of oxygen in the exhaust gas is F exhause O2·Q exhaust It is expressed as. Typically, the incoming gas contains 100% oxygen, and thus the oxygen flow rate corresponds to the total flow rate of the incoming gas. After gas exchange occurs, the oxygen concentration in the exhaust gas (or "consumed" sweep gas) may still be relatively high, such as approximately 95%. However, it should be understood that the oxygen concentration in the exhaust gas may vary depending on several factors, such as the gas exchange efficiency between the sweep gas and circulating blood, the blood flow rate, the oxygen concentration in the sweep gas, the oxygen saturation in the oxygen-deficient blood, and the concentration of hemoglobin.

[0062] As previously mentioned, the flow rate of oxygen in the incoming gas may be predetermined by the operation setting controlling the gas blender (130), whereas the flow rate of oxygen in the exhaust gas may be approximated by the flow rate of any oxygen absorbed by the blood during gas exchange in the oxygen-gas exchange device (110) in the incoming gas. Therefore, by determining the flow rate of oxygen absorbed by the blood and comparing it with the flow rate of oxygen supplied to the gas exchange device (110), the flow rate released by the gas exchange device (110) can be estimated.

[0063] FIG. 2 is a flowchart of a method used to determine the flow rate of oxygen exiting the gas exchange device (110) and to calculate the total flow rate of exhaust gas emitted by the gas exchange device (110). The total flow rate of exhaust gas may now be used to determine the exchange rate of carbon dioxide, which is an indicator of the overall performance or condition of the gas exchange device (110), as will be discussed later.

[0064] The gas exchange device (110) may be part of a system (100) similar to that discussed in FIG. 1, and may be accordingly coupled to the patient's circulatory system to provide oxygen-rich blood by exposing oxygen-deficient blood to oxygen in a sweep gas passing through the gas region (117) of the gas exchange device (110).

[0065] The method involves the step (210) of receiving sensor data indicating the oxygen content in oxygen-rich blood and the oxygen content in oxygen-deficient blood. Oxygen content may refer to the total concentration of oxygen dissolved in plasma and oxygen bound to hemoglobin. Typically, a major portion of oxygen is bound to hemoglobin, while a smaller proportion (such as approximately 1.5–3% of the total oxygen concentration) is directly dissolved in plasma. In the following, examples of methods for determining each concentration will be discussed with reference to FIGS. 1 and FIGS. 2.

[0066] The concentration of oxygen bound to hemoglobin is proportional to a parameter referred to as blood oxygen saturation, which can be understood as the ratio of available oxygen binding sites on hemoglobin occupied by oxygen molecules. In healthy adult individuals, oxygen saturation in oxygen-rich blood is usually between 95% and 100%, whereas oxygen saturation in oxygen-deficient blood is usually between 60% and 80%.

[0067] Hemoglobin is known to be able to carry 1.34 mL of oxygen per gram when fully saturated with oxygen. The concentration of hemoglobin in the blood varies from person to person and is preferably measured for each individual patient. Typically, hemoglobin levels range from 13.5 to 18 g / dL for adult males, from 12 to 15 g / dL for adult females, and from 11 to 16 g / dL for children. The total concentration of oxygen bound to hemoglobin may therefore be proportional to the concentration of hemoglobin in the blood and oxygen saturation.

[0068] The concentration of oxygen dissolved in plasma can be considered to be directly proportional to the partial pressure of oxygen in the blood and can be calculated using a relationship referred to as Henry's Law. At body temperature, it is known that approximately 0.0033 mL of oxygen is dissolved in 1 mL of plasma per mmHg of partial pressure of oxygen.

[0069] The aforementioned relationship can be used to determine the concentration of oxygen, or the oxygen content in oxygen-rich blood and oxygen-deficient blood. As a result, the oxygen uptake (VO2) in the blood (e.g., in L / min) is determined (220) by comparing the concentration of oxygen in oxygen-rich blood and the concentration of oxygen in oxygen-deficient blood:

[0070] [Mathematical Formula 1]

[0071]

[0072] Q blood is the blood flow rate (L / min), Hb is the hemoglobin concentration (g / dL), and S a O2 is the oxygen saturation (%) in oxygen-rich blood, and S v O2 is the oxygen saturation (%) in oxygen-deficient blood, and p a O2 is the partial pressure of oxygen (mmHg) in oxygen-rich blood, and p v O2 is the partial pressure of oxygen (mmHg) in oxygen-deficient blood.

[0073] As previously discussed, the blood flow rate may be predetermined by an operation setting controlling the pump unit (107), while data indicating the oxygen concentration in the blood may be retrieved from the sensor devices (122, 123). In this example, an oximeter may be used to measure the concentration of oxygen bound to hemoglobin in oxygen-rich blood and oxygen-deficient blood, whereas a sensor such as an optode or Clark electrode may be used to measure the concentration of oxygen dissolved in the plasma of the oxygen-rich blood and oxygen-deficient blood, respectively. The first sensor device (122) and the second sensor device (123) may therefore each include an oximeter and a Clark electrode. The oximeter measures oxygen saturation (S a O2, S v While it can be used to generate sensor data indicating O2) and hemoglobin concentration in blood, the Clark electrode is used for partial pressure (p a O2, p v It may also be used to generate sensor data representing O2. As shown in FIG. 1, the first sensor device (122) may be located at the outlet of the gas exchange device (110) and the second sensor device (123) may be located at the inlet of the gas exchange device (110).

[0074] The flow rate of oxygen in the incoming gas may be determined (230) based on the oxygen concentration of the incoming gas and the total flow rate of the incoming gas. As previously mentioned, these parameters may be known from the settings controlling the operation of the gas blender (130). The gas blender (130) may be configured to deliver, for example, a total incoming flow rate of 4 L / min and an oxygen concentration of 80% or 100% oxygen. However, it should be understood that in some examples, the total incoming flow rate and / or oxygen concentration may be determined by one or more sensors, such as a flow meter or sensor, for measuring the oxygen concentration.

[0075] The flow rate of oxygen in the exhaust gas may be determined (240) based on the difference between the flow rate of oxygen in the incoming gas and the oxygen absorption rate in the blood. This is based on the realization that a major portion of the oxygen supplied to the gas exchange device (110) is absorbed by the blood or transferred to the exhaust gas flow as excess oxygen. This relationship may also be expressed as follows:

[0076] [Mathematical Formula 2]

[0077]

[0078] Here, VO2 is the oxygen uptake in the blood as previously determined, and F inlet O2 is the concentration of oxygen in the incoming gas, and Q inlet is the flow rate of the incoming gas, and F exhaust O2 is the concentration of oxygen in the exhaust gas, and Q exhust Q is the total flow rate of the exhaust gas. exhaust If we find the solution for:

[0079] [Mathematical Formula 3]

[0080]

[0081] is. Oxygen concentration in exhaust gas (F exhaustO2) can be recovered from sensor data received (250) from a sensor device (124) placed at the outlet (114) of a gas exchange device (110), as illustrated in the example of FIG. 1. The oxygen concentration may then be used in conjunction with the preceding Equation 3 to determine the total flow rate of the exhaust gas.

[0082] In some examples, the total flow rate of the exhaust gas may be used to determine (280) the flow rate of carbon dioxide in the exhaust gas. The flow rate of carbon dioxide may be determined based on the concentration of carbon dioxide in the exhaust gas and the total flow rate of the exhaust gas. The concentration of carbon dioxide may be received (270) from a carbon dioxide sensor that may be included in a sensor device (124) at the outlet (114) of the gas exchange device (110). Examples of carbon dioxide sensors include, but are not limited to, an infrared sensor that correlates the level of absorption of infrared light by carbon dioxide molecules with the concentration of carbon dioxide molecules in the exhaust gas.

[0083] The concentration or flow rate of carbon dioxide in the exhaust gas may be used to determine the state (290) of the gas exchange device (110). More specifically, the concentration or flow rate of carbon dioxide may be compared to a reference value, such as a threshold concentration or flow rate. If the concentration or flow rate of carbon dioxide meets or exceeds the threshold concentration or flow rate, this may indicate that the gas exchange device (110) is functioning well and thus can provide the intended gas-exchange rate. If the concentration or flow rate of carbon dioxide is lower than the threshold rate, this may indicate that the performance of the membrane (119) has deteriorated and the gas exchange device (110) may require service or replacement.

[0084] It should be understood that the term "condition" of the gas exchange device (110) generally refers to the condition or performance level of the gas exchange device (110). In a well-functioning, i.e., normal state, the gas exchange device (110) may provide a gas exchange rate within an acceptable range. This condition may be determined by comparing the concentration or flow rate of carbon dioxide in the exhaust gas to a reference measurement. In a deteriorated or malfunctioning state, the performance of the gas exchange device (110) may have dropped from its normal level. In this state, the membrane (119) may not be able to facilitate the intended exchange of blood gas. In other examples, the gas exchange device (110) may still function, but there may be a risk that it will not function properly. In other words, patient safety may be a trade-off. Terms such as "deteriorated," "damaged," or "service required" may be used to describe this condition.

[0085] The system (100) of the present disclosure may generally include one or more processors (140) and one or more non-transient computer-readable media, the media first storing computer-executable instructions, which, when executed by one or more processors, cause the system (100) to execute at least a portion of the operation illustrated in FIG. 2 and described above.

[0086] Generally, the system (100) may include circuits configured to implement the functions described herein (using one or more non-transient computer-readable media). Suitable processors for executing the program of instructions include, for example, general-purpose and special-purpose microprocessors, and one of a single processor or multiple processors or cores of any type of computer. The processor may be supplemented or combined with an application-specific integrated circuit (ASIC). Those skilled in the art will understand that the exemplary embodiments described above may be implemented with any suitable software, hardware, or firmware configuration or combination thereof. Exemplary hardware platforms for implementing the exemplary embodiments may include, for example, Intel x86-based platforms with compatible operating systems, Windows OS, Mac platforms, and mobile devices with operating systems such as MAC OS, iOS, Android, etc. In additional examples, an exemplary embodiment of the method described above may be implemented as a program comprising lines of code stored on a non-transient computer-readable storage medium that may be executed on a processor or microprocessor when compiled.

[0087] Furthermore, modifications to the disclosed embodiments may be understood and realized by those skilled in the art when practicing the claimed invention from the study of the drawings, the disclosure, and the appended claims. In addition, preferred embodiments of the invention are disclosed in the drawings and the specification, and although specific terms are used, these terms are used only in a general and descriptive sense and are not used for limiting purposes. The scope of the invention is set forth in the following claims, and the word “comprising” does not exclude other elements or steps, and elements in the singular form (‘a’ or ‘an’) do not exclude the plurality.

Claims

Claim 1 A method (200) for determining the total flow rate of exhaust gas exiting a gas exchange device coupled to a patient's circulatory system, wherein the gas exchange device is configured to provide oxygen-rich blood to the circulatory system by exposing the patient's oxygen-deficient blood to oxygen provided by an incoming gas, and to allow the passage of excess oxygen into the exhaust gas, the method comprises: receiving sensor data indicating the oxygen content in the oxygen-rich blood and the oxygen content in the oxygen-deficient blood (210); determining the oxygen uptake in the blood based at least partially on the difference between the oxygen content in the oxygen-rich blood and the oxygen content in the oxygen-deficient blood and the blood flow rate through the gas exchange device (220); determining the flow rate of oxygen in the incoming gas based at least partially on the oxygen concentration in the incoming gas and the total flow rate of the incoming gas (230); determining the flow rate of oxygen in the exhaust gas based at least partially on the difference between the oxygen flow rate in the incoming gas and the oxygen uptake in the blood (240); and receiving sensor data indicating the oxygen concentration in the exhaust gas (250). A method comprising the step (260) of determining the total flow rate of exhaust gas based at least partially on the flow rate of oxygen in the exhaust gas and the oxygen concentration in the exhaust gas. Claim 2 A method according to claim 1, wherein the sensor data representing the oxygen content in oxygen-rich blood and the oxygen content in oxygen-deficient blood represents the amount of oxygen bound to hemoglobin in each of the oxygen-rich blood and oxygen-deficient blood, and the amount of oxygen dissolved in the plasma of each of the oxygen-rich blood and oxygen-deficient blood. Claim 3 A method according to claim 2, wherein the sensor data representing the amount of oxygen dissolved in the plasma of each oxygen-rich blood and oxygen-poor blood is measured by each blood gas sensor. Claim 4 A method according to any one of claims 1 to 3, further comprising the step of reducing the temperature of the exhaust gas; and then the step of exposing a sensor to the exhaust gas, wherein the sensor is configured to generate sensor data indicating the oxygen concentration in the exhaust gas. Claim 5 A method according to claim 4, comprising the step of reducing the temperature of the exhaust gas to ambient temperature. Claim 6 A method according to claim 4 or claim 5, wherein the sensor is integrated into the gas exchange device. Claim 7 A method according to any one of claims 1 to 6, further comprising: receiving sensor data indicating the carbon dioxide concentration in the exhaust gas (270); determining the flow rate of carbon dioxide in the exhaust gas based at least partially on the total flow rate of the exhaust gas and the carbon dioxide concentration (280); and determining the state of the exhaust exchange device based at least partially on whether the flow rate of carbon dioxide satisfies or exceeds a threshold flow rate (290). Claim 8 A method according to any one of claims 1 to 7, wherein the blood flow rate, the oxygen concentration in the incoming gas, and the total flow rate of the incoming gas are each predetermined parameters. Claim 9 A system (100) for exchanging blood and one or more gases in the circulatory system of a patient (10), comprising a gas exchange device (110) including a gas inlet (112) for receiving an incoming gas and an outlet (114) for releasing an exhaust gas, wherein the gas exchange device is configured to provide oxygen-rich blood by exposing the patient's oxygen-deficient blood to oxygen provided by the incoming gas and to allow the passage of excess oxygen into the exhaust gas; a sensor device (120) configured to generate sensor data indicating the oxygen content in the oxygen-rich blood, the oxygen content in the oxygen-deficient blood, and the oxygen concentration in the exhaust gas; and one or more processors. A system comprising one or more non-transient computer-readable media storing instructions executable by one or more processors, wherein, when the instructions are executed, the system performs operations including: determining the oxygen absorption rate in blood based at least partially on the difference between the oxygen content in oxygen-rich blood and the oxygen content in oxygen-deficient blood and the blood flow rate through the gas exchange device; determining the oxygen flow rate in the incoming gas based at least partially on the oxygen concentration in the incoming gas and the total flow rate of the incoming gas; determining the oxygen flow rate in the exhaust gas based at least partially on the difference between the oxygen flow rate in the incoming gas and the oxygen absorption rate in blood; and determining the total flow rate of the exhaust gas based at least partially on the oxygen flow rate in the exhaust gas and the oxygen concentration in the exhaust gas. Claim 10 In claim 9, the gas exchange device further comprises an emergency outlet (116), and through the emergency outlet (116), at least a portion of the exhaust gas is discharged, in a system Claim 11 A system according to claim 9 or claim 10, wherein the sensor device comprises: a first oxygen meter positioned to measure the oxygen saturation level of oxygen-rich blood and a second oxygen meter positioned to measure the oxygen saturation level of oxygen-deficient blood; and a first blood gas sensor positioned to measure the partial pressure of oxygen in oxygen-rich blood and a second blood gas sensor positioned to measure the partial pressure of oxygen in oxygen-deficient blood. Claim 12 A system according to claim 9 or claim 10, wherein the operation further comprises at least one of the steps of: determining an oxygen saturation level of oxygen-rich blood based on the partial pressure of oxygen-rich blood; and determining an oxygen saturation level of oxygen-deficient blood based on the partial pressure of oxygen-deficient blood.

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