Calculation device, extracorporeal circulation system, and calculation method

Abstract

To acquire a recirculation rate by low invasive procedures.SOLUTION: A calculation device 30 for calculating a recirculation rate indicating an extent of an amount of blood recirculating from a blood removal line 12 of blood sending side blood sent from a blood sending line 13 includes; an acquisition unit 33 for acquiring a blood removal side average, which is an average of oxygen saturation degrees of blood removal side blood removed from the blood removal line 12 and a blood removal side minimum value, which is a minimum value of the oxygen saturation degree of the blood removal side blood; and a calculation unit 31 for calculating a recirculation rate using a value obtained on the basis of the blood removal side average and the blood removal side minimum value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a device and method for calculating a recirculation ratio, and an extracorporeal circulation system equipped with the device. [Background technology]

[0002] Patent Document 1 discloses an extracorporeal circulation system, which is an artificial heart-lung system. The extracorporeal circulation system includes a blood removal line and a blood supply line. The extracorporeal circulation system also includes a blood supply pump and an artificial lung. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-178750 Summary of the Invention [Problem to be solved by the invention]

[0004] When blood drawn from a patient is recirculated back to the patient using an extracorporeal circulation system, some of the blood recirculated from the blood removal line without circulating through the systemic circulation (hereinafter referred to as "recirculation"). For example, when performing V-VECMO (Veno-Venous Extracorporeal Membrane Oxygenation), it is necessary to maintain a high level of respiratory support for the patient. To achieve this, it is necessary to prevent the amount of blood recirculated from the blood removal line without circulating through the systemic circulation (hereinafter referred to as "recirculation rate") from becoming excessively high.

[0005] For example, the recirculation rate can be calculated by measuring the oxygen saturation of mixed venous blood, which is a mixture of superior vena cava blood, inferior vena cava blood, and coronary vein blood. For example, as shown in the following formula 1, the recirculation rate (R) is calculated by multiplying the oxygen saturation (Spre It can be calculated by subtracting the mixed venous oxygen saturation (SvO2) from the oxygen saturation (O2) and dividing the result by the value obtained by subtracting the mixed venous oxygen saturation from 1.

[0006] R=(S pre O2-SvO2) ÷ (1-SvO2) (Equation 1)

[0007] However, measuring mixed venous oxygen saturation requires inserting a cannula into the patient's pulmonary veins or right ventricle, which is highly invasive and often difficult to implement. Therefore, there is a need for a minimally invasive method to obtain recirculation fraction. [Means for solving the problem]

[0008] A calculation device according to one aspect of the present invention calculates a recirculation rate indicating the extent of the amount of blood recirculating from a blood removal line out of the blood transfer-side blood transferred from a blood transfer line, and includes an acquisition unit that acquires a blood removal-side average value, which is the average value of the oxygen saturation of the blood transfer-side blood removed from the blood removal line, and a blood removal-side minimum value, which is the minimum value of the oxygen saturation of the blood transfer-side blood, and a calculation unit that calculates the recirculation rate using a value obtained based on the blood removal-side average value and the blood removal-side minimum value.

[0009] An extracorporeal circulation system according to another aspect of the present invention includes the above-described calculation device, a blood feed pump that feeds the blood on the blood feed side, and a display unit that displays the calculated recirculation rate.

[0010] Furthermore, a calculation method according to another aspect of the present invention is a calculation method for calculating a recirculation rate indicating the extent of the amount of blood recirculating from the blood removal line out of the blood transfer side blood transferred from the blood transfer line, in which a blood removal side average value, which is the average value of the oxygen saturation of the blood transfer side blood removed from the blood removal line, and a blood removal side minimum value, which is the minimum value of the oxygen saturation of the blood transfer side blood, are obtained, and the recirculation rate is calculated using a value obtained based on the blood removal side average value and the blood removal side minimum value. [Effects of the Invention]

[0011] This allows the recirculation rate to be obtained using a minimally invasive technique.

[0012] Further features of the invention will become apparent from the following description of an embodiment thereof, given by way of example only and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0013] [Figure 1] Schematic overall diagram of the extracorporeal circulation system. [Figure 2] Schematic diagram of the tricuspid valve when it is open. [Figure 3] Schematic diagram of the tricuspid valve when closed. [Figure 4] 1 is a schematic graph showing oxygen saturation in a state of low recirculation rate. [Figure 5] 1 is a schematic graph showing oxygen saturation in the presence of high recirculation rates. [Figure 6] 10 is a flowchart of a calculation process. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, exemplary embodiments for carrying out the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of components described in the following embodiments can be arbitrarily set and can be changed depending on the configuration of the device to which the present invention is applied or various conditions. Furthermore, unless otherwise specified, the scope of the present invention is not limited to the embodiments specifically described below.

[0015] As shown in Fig. 1, the extracorporeal circulation system 100 performs extracorporeal circulation of the blood of a patient P. For example, the extracorporeal circulation system 100 circulates the blood of the patient P and adds oxygen to and removes carbon dioxide from the blood. To this end, the extracorporeal circulation system 100 includes a blood removal line 12, which is an example of a blood removal circuit, and a blood transfer line 13, which is an example of a blood transfer circuit for transferring blood.

[0016] Furthermore, the extracorporeal circulation system 100 includes a blood feed pump 14, a control unit 30 which is an example of a calculation device, and a display unit 60. The control unit 30 which is a calculation device calculates a recirculation rate which indicates the amount of blood that is not circulated through the body and is recirculated from the blood removal line 12 out of the blood feed side blood that is blood fed from the blood feed line 13. The blood feed pump 14 feeds the blood feed side blood into the body of the patient P via the blood feed line 13. The display unit 60 displays the calculated recirculation rate.

[0017] The display unit 60 may be a single display or may have multiple displays. The display unit 60 is connected to the control unit 30 by wire or wirelessly. As an example, the display unit 60 displays the oxygen saturation level in addition to the recirculation rate. The display unit 60 may also display the heart rate of the patient P, the average value on the blood removal side, the minimum value on the blood removal side, and the average value on the blood supply side.

[0018] Furthermore, the extracorporeal circulation system 100 includes an oxygenator 15 that expels carbon dioxide from the blood and adds oxygen to the blood.

[0019] The extracorporeal circulation system 100 further includes a heartbeat measuring device 17 that measures the heartbeat of the patient P. For example, the heartbeat measuring device 17 is attached to the patient P and is an electrocardiograph, an electrocardiogram analyzer, or a heartbeat monitor. The heartbeat measuring device 17 transmits the measured heartbeat to the control unit 30. The control unit 30 includes a storage unit (not shown) that stores the heartbeat in association with the measurement time. The measurement time of the heartbeat is synchronized with the detection time so that it can be displayed on the same time axis as the detection time of oxygen saturation, which will be described later. Alternatively, the heartbeat measuring device 17 may be provided separately from the extracorporeal circulation system 100, and the extracorporeal circulation system 100 may acquire information from the heartbeat measuring device 17.

[0020] The blood removal line 12 is provided with a blood removal-side sensor S1 that detects oxygen saturation. The blood return line 13 is provided with a blood return-side sensor S2 that detects oxygen saturation. The blood removal-side sensor S1 detects the oxygen saturation of the blood flowing through the blood removal line 12 and sends it to the control unit 30. The blood return-side sensor S2 detects the oxygen saturation of the blood flowing through the blood return line 13 and sends it to the control unit 30. The memory unit of the control unit 30 stores the oxygen saturation of the blood on the removal side and the blood return side in association with the time of detection.

[0021] Furthermore, the blood removal line 12 is provided with a blood removal flow rate adjustment unit (not shown). This blood removal flow rate adjustment unit adjusts the blood removal flow rate according to the rotation speed of the motor of the blood feed pump 14. Specifically, the blood removal flow rate increases as the rotation speed of the motor increases, and decreases as the rotation speed of the motor decreases. Alternatively, the blood removal flow rate adjustment unit may have a clamping member and its drive unit. The clamping amount (clamping amount) of the blood removal flow rate adjustment unit can be adjusted manually or by the driving force of a drive unit such as a motor. This changes the cross-sectional area of ​​the blood removal line 12, making it possible to adjust the blood removal flow rate through the blood removal line 12. Furthermore, a sensor for detecting the blood removal flow rate and a sensor for detecting blood concentration may be connected to the blood removal line 12.

[0022] Furthermore, the blood remittance line 13 may be provided with a blood remittance flow rate adjusting unit (not shown). One example of this blood remittance flow rate adjusting unit is a clamping member, and the clamping amount can be adjusted manually or by driving force from a connected motor. This changes the cross-sectional area of ​​the blood remittance line 13, thereby adjusting the blood remittance flow rate through the blood remittance line 13. The blood remittance line 13 may also be provided with a sensor for detecting the blood remittance flow rate and a sensor for detecting blood concentration.

[0023] The blood feed pump 14 is a centrifugal pump that rotates an impeller blade with a motor to feed blood to the oxygenator 15. The rotation speed of the motor of the blood feed pump 14 is controlled by a control signal output from the flow rate control unit 32. The blood feed pump 14 feeds blood at a flow rate that corresponds to the increased or decreased rotation speed. Alternatively, the blood feed pump 14 may be a roller pump in which a rotating roller rotates and compresses a tube, thereby sucking and pushing out blood from the tube.

[0024] The oxygenator 15 is equipped with, for example, a hollow fiber membrane or a flat membrane with excellent gas permeability, and expels carbon dioxide from the blood and adds oxygen. The oxygenator 15 also has a heat exchanger for adjusting the temperature of the blood.

[0025] In the blood removal line 12, blood removal-side blood (hereinafter also referred to as venous blood) removed from the patient P via a blood removal cannula 121 (FIG. 2) flows. The venous blood is then sent to an oxygenator 15 by a blood transfer pump 14 and circulated to the patient P via the blood transfer line 13. That is, blood transfer-side blood (hereinafter also referred to as arterial blood) is sent to the patient P via the blood transfer line 13 and a blood transfer cannula 131 (FIG. 2). As an example, the blood removal line 12, the blood transfer line 13, and the blood line 16 have tubes made of polyvinyl chloride.

[0026] Specifically, venous blood before oxygenation, which has been withdrawn or introduced outside the body of patient P, is sent to the oxygenator 15. The oxygenator 15 separates air bubbles from the venous blood using a filter disposed on the outer periphery of the heat exchanger. The oxygenator 15 then adjusts the temperature of the venous blood using the heat exchanger. The oxygenator 15 then arterializes the venous blood via the gas exchange element using the gas exchanger (i.e., adds oxygen and removes carbon dioxide). The oxygenator 15 separates clots from the oxygenated arterial blood using a filter disposed on the inner periphery of the gas exchanger. The arterial blood is then sent to patient P through the blood sending line 13.

[0027] The extracorporeal circulation system 100 may also be provided with a line filter for removing air bubbles, foreign matter, and white blood cells from the extracorporeally circulating blood, or a heat exchanger for cooling and heating the blood.

[0028] [About the control system] The control unit 30 of the extracorporeal circulation system 100 controls the blood pump 14 and other components. As an example, the control unit 30 is a computer having a processor (not shown) and a memory serving as a storage unit storing a control program. The processor is, for example, a central processing unit (CPU) or a microprocessing unit (MPU), and controls the entire extracorporeal circulation system 100 and various processes based on the program stored in the memory. The memory includes a random access memory (RAM), which is a system work memory for the processor's operation, as well as a read-only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), or other computer-readable non-transitory storage medium for storing programs and system software. An example in which the CPU executes various processing operations, such as calculations, controls, and determinations, in accordance with the control program stored in the ROM or HDD will be described below.

[0029] An operation unit (not shown) including a keyboard or various switches for inputting predetermined commands and data is connected by wire or wirelessly to the control unit 30. Furthermore, the control unit 30 can also perform control according to a program stored in a portable recording medium such as a CD (Compact Disc), a DVD (Digital Versatile Disc), a CF (Compact Flash) card, or a USB (Universal Serial Bus) memory, or in an external storage medium such as a server on the Internet.

[0030] Furthermore, the control unit 30 includes a calculation unit 31, a flow rate control unit 32, and an acquisition unit 33. The calculation unit 31 calculates the recirculation rate based on a calculation program stored in the storage unit of the control unit 30. The calculation unit 31, the flow rate control unit 32, and the acquisition unit 33 are logical devices, and are realized by a combination of the hardware resources of the control unit 30 and the calculation program or control program as software resources.

[0031] The calculation unit 31 calculates the recirculation rate using a value obtained based on the blood removal side average value, which is the average value of the oxygen saturation of the blood on the blood removal side removed from the blood removal line 12 acquired by the acquisition unit 33, and the blood removal side minimum value, which is the minimum value of the oxygen saturation of the blood on the blood removal side. Specifically, the calculation unit 31 calculates the recirculation rate using the blood removal side average value (S pre Ave to the lowest value on the blood withdrawal side (S pre The calculation unit 31 calculates the recirculation rate (R) using the value obtained by subtracting the blood removal side minimum value from the blood removal side average value. That is, the calculation unit 31 calculates the recirculation rate by dividing the value obtained by subtracting the blood removal side minimum value from the blood removal side average value by the value obtained by subtracting the blood removal side minimum value from 100.

[0032] R=(S pre Ave-S pre Min)÷(100-S pre Min) (Equation 2)

[0033] Furthermore, the calculation unit 31 calculates the value obtained by subtracting the blood removal side minimum value from the blood removal side average value as the blood sending side average value (S post Ave to the lowest value on the blood withdrawal side (S pre The recirculation rate may be calculated by dividing the recirculation rate by the value obtained by subtracting the average value (Min) from the average value (Min). Specifically, the calculation unit 31 may calculate the recirculation rate using the following formula 3. However, the oxygen saturation of the blood on the blood sending side can be maintained at approximately 100%. Therefore, by calculating the recirculation rate based on the blood removal side average value and the blood removal side minimum value as shown in the above formula 2, it is possible to omit the use of the oxygen saturation of the blood on the blood sending side.

[0034] R=(S pre Ave-S pre Min)÷(S post Ave-S pre Min) (Equation 3)

[0035] For example, if the average value on the blood removal side is 84%, the minimum value on the blood removal side is 75%, and the average value on the blood return side is 99%, the recirculation rate obtained according to Equation 3 is 37.5% (=(84-75)÷(99-75)).

[0036] The acquisition unit 33 acquires a blood removal-side average value, which is the average value of the oxygen saturation of the blood removed from the blood removal line 12, and a blood removal-side minimum value, which is the minimum value of the oxygen saturation of the blood removed from the blood removal line 12. Furthermore, the acquisition unit 33 may acquire a blood sending-side average value, which is the average value of the oxygen saturation of the blood sending from the blood sending line 13. For example, the acquisition unit 33 acquires the oxygen saturation of the blood removed from the blood removal-side blood and the blood sending-side blood stored in the memory unit of the control unit 30.

[0037] Furthermore, the acquisition unit 33 acquires the blood removal-side minimum value for a predetermined length of time, and calculates and acquires the blood removal-side average value and the blood feeding-side average value for the predetermined length of time. As an example, the acquisition unit 33 acquires the heart rate of the patient P stored in the memory unit of the control unit 30. For example, the acquisition unit 33 uses a time corresponding to a predetermined heart rate as the predetermined length of time. Then, the acquisition unit 33 acquires the blood removal-side average value and the blood removal-side minimum value for the length of time corresponding to the predetermined heart rate.

[0038] As one example, the predetermined number of heart rates is five, and the acquisition unit 33 acquires the blood removal side average value and the blood removal side minimum value during the five heart rate measurements. Alternatively, the acquisition unit 33 may acquire the blood removal side average value and the blood removal side minimum value for a predetermined number of seconds as the predetermined length of time. As one example, when the heart rate is 30 bpm, the acquisition unit 33 acquires the blood removal side average value and the blood removal side minimum value for 10 seconds or 15 seconds. Furthermore, the acquisition unit 33 may acquire the blood removal side average value and the blood removal side minimum value for a predetermined number of seconds (for example, any time between 5 and 15 seconds) regardless of the patient's heart rate.

[0039] The acquisition unit 33 may also acquire the blood removal side average value, blood removal side minimum value, and blood delivery side average value from a gas monitor or blood gas analyzer for extracorporeal circulation separate from the extracorporeal circulation system 100. The gas monitor or blood gas analyzer may be connected to the extracorporeal circulation system 100 by wire or wirelessly. Alternatively, the gas monitor or blood gas analyzer may be part of the extracorporeal circulation system 100.

[0040] The flow rate control unit 32 controls the blood feed pump 14 so as to increase or decrease the flow rate of blood on the blood feed side. The flow rate control unit 32 may further control a blood removal flow rate adjustment unit (not shown) so as to increase or decrease the flow rate of blood on the blood removal side flowing through the blood removal line 12.

[0041] [Recirculation] 2 and 3 schematically show the heart of patient P. FIG. 2 shows a state in which the tricuspid valve is open, and FIG. 3 shows a state in which the tricuspid valve is closed. In the examples of FIGS. 2 and 3, the blood infusion cannula 131 is placed in the ascending vena cava, and the blood removal cannula 121 is placed in the descending vena cava. In other examples, the blood infusion cannula 131 is placed in the ascending vena cava, and the blood removal cannula 121 is placed in the right atrium.

[0042] When circulating the blood of patient P, if the positions of the blood removal cannula 121 and the blood transfer cannula 131 are too close, recirculation may occur, in which arterial blood sent from the blood transfer cannula 131 is sucked directly back into the blood removal cannula 121. This phenomenon is called recirculation, and the ratio of the flow rate of recirculated blood to the flow rate of blood on the blood transfer side corresponds to the recirculation rate. In other words, the recirculation rate indicates the amount of blood sent from the blood transfer line 13 that is recirculated from the blood removal line 12 without being circulated systemically. If the recirculation rate becomes high, the amount of oxygenated arterial blood that is recirculated without being circulated systemically increases, and the role of supporting the lungs is not fulfilled. This results in a decrease in the level of respiratory support for patient P.

[0043] Causes of a high recirculation rate include a decline in the cardiac function of the patient P and misalignment of the blood removal cannula 121 and the blood transfer cannula 131. Therefore, if the recirculation rate is determined to be high, it may be necessary to change the position of the blood removal cannula 121 or the blood transfer cannula 131, perform an echocardiogram, or perform a chest X-ray. As an example, if the recirculation rate is higher than 50% (or 0.5), the recirculation rate is determined to be high.

[0044] The recirculation rate changes depending on whether the tricuspid valve is open or closed, and is linked to the pulsation of the heart. Specifically, when the tricuspid valve is open as shown in FIG. 2, blood sent from the blood sending cannula 131 flows into the right ventricle, resulting in a low recirculation rate. On the other hand, when the tricuspid valve is closed as shown in FIG. 3, the sent blood does not flow into the right ventricle and is more likely to be drawn into the blood removal cannula 121. This change in recirculation rate affects the change in the oxygen saturation of the blood on the blood removal side. Therefore, the recirculation rate can be calculated based on the oxygen saturation of the blood on the blood removal side.

[0045] As an example, Figures 4 and 5 are graphs showing the relationship between the closing timing T1 and opening timing T3 of the tricuspid valve and the oxygen saturation of the blood on the blood removal side. In Figures 4 and 5, the horizontal axis represents elapsed time (seconds). The upper graphs in Figures 4 and 5 show electrical changes in the myocardium, with the vertical axis representing potential difference (mV). The lower graphs in Figures 4 and 5 show changes in oxygen saturation of the blood on the blood removal side, with the vertical axis representing oxygen saturation (%). Figure 4 is a graph showing a state with a low recirculation rate, and Figure 5 is a graph showing a state with a high recirculation rate.

[0046] 4 and 5, the tricuspid valve closing timing T1 coincides with the peak timing of the QRS wave. The tricuspid valve opening timing T3 is the timing when the RT interval, which is the time from the start of the R wave to the end of the T wave, has elapsed since the closing timing T1. Furthermore, the stable timing T2 at which the recirculation rate stabilizes is the timing when the difference ΔS between the minimum and maximum oxygen saturation values ​​of the blood on the blood removal side has elapsed. pre This is when O2 reaches its maximum.

[0047] As shown in Figures 4 and 5, the oxygen saturation of the blood on the withdrawal side increases from the closing timing T1 and stabilizes at the stable timing T2, which is before the opening timing T3. The time Δt from the closing timing T1 to the stable timing T2 is long when the recirculation rate is low (Figure 4) and short when the recirculation rate is high (Figure 5). The maximum oxygen saturation of the blood on the withdrawal side is small when the recirculation rate is low and large when the recirculation rate is high. As an example, when the recirculation rate is high, the maximum oxygen saturation of the blood on the withdrawal side is 75% and the minimum is 63%, and the time Δt from the closing timing T1 to the stable timing T2 is 0.1 seconds. In this case, the difference ΔS between the minimum and maximum oxygen saturation of the blood on the withdrawal side is pre O2 is 12%.

[0048] [Calculation process] The calculation process for calculating the recirculation rate will be described with reference to Fig. 6. For example, the calculation process is executed by a calculation program causing each part of the control unit 30, which is a computer, to function.

[0049] When the extracorporeal circulation system 100 starts extracorporeal circulation of patient P's blood, the blood removal-side sensor S1 detects the oxygen saturation of the blood on the blood removal side, and the blood sending-side sensor S2 detects the oxygen saturation of the blood on the blood sending side (S101). Then, the blood removal-side sensor S1 and the blood sending-side sensor S2 transmit the oxygen saturation to the memory of the control unit 30, and the memory stores the received oxygen saturation. Next, the acquisition unit 33 acquires the oxygen saturation of the blood on the blood removal side and the blood sending side from the memory (S102). Then, the acquisition unit 33 acquires the blood removal-side minimum value, and calculates and acquires the blood removal-side average value and the blood sending-side average value (S103). Furthermore, the acquisition unit 33 may store the blood removal-side minimum value, the blood removal-side average value, and the blood sending-side average value in the memory.

[0050] The calculation unit 31 then calculates the recirculation rate (S104). The calculation unit 31 may calculate the recirculation rate at any time, or may calculate the recirculation rate at a predetermined timing (for example, every minute). Furthermore, the calculation unit 31 may store the calculated recirculation rate in a storage unit. The display unit 60 then displays the recirculation rate calculated by the calculation unit 31 (S105). As a result, the display unit 60 notifies the user of the extracorporeal circulation system 100 of the recirculation rate, and the calculation process ends. The display unit 60 may display a number indicating the recirculation rate, or may display a graph indicating the recirculation rate.

[0051] The acquisition unit 33 calculates the difference ΔS between the minimum and maximum oxygen saturation values ​​of the blood on the blood removal side. pre The display unit 60 may further acquire O2 and the time Δt from the closing timing T1 to the stabilization timing T2. The display unit 60 may also display a graph showing the change in oxygen saturation of the blood on the blood removal side, which is shown at the bottom of FIGS.

[0052] According to the extracorporeal circulation system 100 described above, the recirculation rate can be calculated using a value obtained based on the blood removal side average value and the blood removal side minimum value. Therefore, there is no need to measure the oxygen saturation of mixed venous blood, and the recirculation rate can be obtained using a minimally invasive technique. Furthermore, because the oxygen saturation of blood on the blood removal side can be continuously measured, the recirculation rate can be continuously calculated and monitored. This allows the user of the extracorporeal circulation system 100 (e.g., a medical professional) to take necessary measures to prevent the recirculation rate from becoming excessively high.

[0053] Although the present invention has been described above with reference to each embodiment, the present invention is not limited to the above-described embodiments. The present invention also includes inventions that have been modified without departing from the scope of the present invention, and inventions equivalent to the present invention. Furthermore, each embodiment and each modified form can be combined as appropriate without departing from the scope of the present invention.

[0054] For example, the calculation device may be separate from the control device of the extracorporeal circulation system 100. That is, the calculation device may be a computer separate from the control unit 30. In this case, the calculation device may further include a calculation unit 31, an acquisition unit 33, and a display unit 60 that displays the recirculation rate. The extracorporeal circulation system 100 can also be used when performing V-VAECMO, in which a cannula is placed in an artery such as the femoral artery to send blood. [Explanation of symbols]

[0055] 12: Blood removal line 13: Blood line 14: Blood pump 30: Control unit (calculation device) 31: Calculation section 33: Acquisition part 60:Display section 100: Extracorporeal circulation system

Claims

1. A calculation device for calculating a recirculation rate indicating the amount of blood recirculating from a blood removal line out of blood sent from a blood sending line, an acquisition unit that acquires a blood removal-side average value, which is an average value of the oxygen saturation of blood on the blood removal side that is removed from the blood removal line, and a blood removal-side minimum value, which is a minimum value of the oxygen saturation of the blood on the blood removal side; a calculation unit that calculates the recirculation rate using a value obtained based on the blood removal side average value and the blood removal side minimum value.

2. 2. The calculation device according to claim 1, wherein the calculation unit calculates the recirculation rate by dividing a value obtained by subtracting the blood removal side minimum value from the blood removal side average value by a value obtained by subtracting the blood removal side minimum value from 100.

3. 2. The calculation device according to claim 1, wherein the calculation unit calculates the recirculation rate by dividing a value obtained by subtracting the blood removal-side minimum value from the blood removal-side average value by a value obtained by subtracting the blood removal-side minimum value from the blood sending-side average value, which is an average value of the oxygen saturation of the blood on the blood sending side.

4. The calculation device according to claim 1 , wherein the acquisition unit acquires the blood removal-side average value and the blood removal-side minimum value over a predetermined length of time.

5. The calculation device according to claim 4 , wherein the acquisition unit acquires a heart rate of the patient and acquires, as the predetermined length of time, the blood removal side average value and the blood removal side minimum value for a time period corresponding to a predetermined heart rate.

6. A calculation device according to any one of claims 1 to 5; a blood sending pump that sends blood on the blood sending side; and a display unit that displays the calculated recirculation rate.

7. A method for calculating a recirculation rate indicating the amount of blood recirculating from a blood removal line out of blood sent from a blood sending line, the method comprising: The computer a blood removal-side average value, which is an average value of the oxygen saturation of the blood removed from the blood removal line, and a blood removal-side minimum value, which is a minimum value of the oxygen saturation of the blood removed from the blood removal line, are obtained; A calculation method for calculating the recirculation rate using a value obtained based on the blood removal side average value and the blood removal side minimum value.

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