Body fluid amount evaluation device and computer program for evaluating body fluid amount

Abstract

This body fluid amount evaluation device comprises a pulse pressure acquisition unit, a first calculation unit, a second calculation unit, and an evaluation unit. The pulse pressure acquisition unit acquires a first pulse pressure of a dialysis patient before returning blood in a dialyzer and a blood circuit, and a second pulse pressure of the dialysis patient at completion of returning the blood. The pulse pressure acquisition unit acquires the first pulse pressure and the second pulse pressure in a plurality of consecutive dialyses of the dialysis patient. The first calculation unit calculates the increase rate of the pulse pressure from the first pulse pressure and the second pulse pressure. The first calculation unit calculates the increase rate of the pulse pressure for each of the plurality of dialyses from the first pulse pressure and the second pulse pressure in each of the plurality of dialyses. The second calculation unit calculates an average value and / or an index that indicates variation of the increase rates of the pulse pressure in the plurality of dialyses. The evaluation unit evaluates the body fluid amount of the dialysis patient on the basis of the average value and / or the index that indicates variation which has been calculated by the second calculation unit.

Description

Body fluid volume evaluation device and computer program for evaluating body fluid volume

[0001] The present specification relates to a technique for evaluating the body fluid volume of a dialysis patient at the end of dialysis.

[0002] In dialysis patients, kidney function is lost, so all ingested water accumulates in the body. Excessive water retention in the body can lead to edema, hypertension, or both. Excess water is removed through dialysis, but if the volume of bodily fluids decreases excessively during or at the end of dialysis, blood pressure drops. This phenomenon is called dialysis hypotension. When dialysis hypotension occurs, the blood and oxygen supply to various organs decreases, resulting in symptoms specific to each organ, such as abdominal discomfort, yawning, sighing, nausea, vomiting, muscle cramps, restlessness, dizziness, loss of consciousness, and anxiety. An excessive reduction in blood and oxygen supply to various organs is called ischemia of the respective organ.

[0003] In dialysis, the principle is to remove fluid so that the patient's body fluid volume at the end of dialysis is equal to that of a healthy individual with the same body type. To achieve this, the body fluid volume of a healthy individual with the same body type must be known. However, no accurate method exists. Therefore, at present, dry body weight is defined by trial and error as the weight at which there is no edema at the end of dialysis, no drop in blood pressure during dialysis, no fatigue after dialysis, and no hypertension during non-dialysis (e.g., Charra B, et al.: Clinical Determination of Dry Body Weight. Hemodial Int 5: 42-50, 2001). Fluid removal is then performed so that the patient's weight at the end of dialysis is equal to the dry body weight.

[0004] As mentioned above, during dialysis, fluid is removed from the patient until their weight reaches their dry weight. Therefore, it is necessary to set the dry weight appropriately. However, until now, the only way to know whether the dry weight is appropriate has been to observe the changes in blood pressure during dialysis and detect the appearance of the above-mentioned clinical symptoms.

[0005] The present specification discloses a technique for appropriately evaluating whether a dialysis patient's dry weight is appropriate.

[0006] In a first aspect of the technology disclosed in this specification, a body fluid volume evaluation device evaluates the body fluid volume of a dialysis patient at the end of dialysis. The body fluid volume evaluation device includes a pulse pressure acquisition unit, a first calculation unit, a second calculation unit, and an evaluation unit. The pulse pressure acquisition unit acquires a first pulse pressure, which is the pulse pressure of the dialysis patient at the end of dialysis before blood in the dialyzer and blood circuit is returned to the body of the dialysis patient, and a second pulse pressure, which is the pulse pressure of the dialysis patient at the end of blood return. The pulse pressure acquisition unit acquires the first pulse pressure and the second pulse pressure over multiple consecutive dialysis sessions of the dialysis patient. The first calculation unit calculates an increase rate of the pulse pressure from the first pulse pressure and the second pulse pressure. The first calculation unit calculates an increase rate of the pulse pressure for each of the multiple dialysis sessions from the first pulse pressure and the second pulse pressure. The second calculation unit calculates at least one of an index indicating the average value and a variation of the increase rate of the pulse pressure over the multiple dialysis sessions calculated by the first calculation unit. The evaluation unit evaluates the body fluid volume of the dialysis patient based on at least one of the average value and the index indicating the variation calculated by the second calculation unit.

[0007] If excessive fluid remains in the body even at the end of dialysis, edema is observed at the end of dialysis. In this case, the degree of edema generally parallels the excess volume of body fluid. On the other hand, excessive loss of body fluid volume during or at the end of dialysis can lead to dialysis hypotension, postdialysis fatigue, or both. However, dialysis hypotension and postdialysis fatigue do not occur every dialysis session, even if the fluid deficit remains unchanged. These symptoms occur in some dialysis sessions and not in others. This is likely because, although excessive loss of body fluid volume is the cause of these symptoms, factors such as the rate of water removal and physical condition (presence of inflammation in the body) likely facilitate their onset. Careful observation reveals that the proportion of dialysis sessions in which these symptoms occur increases with a larger fluid deficit, while the proportion of dialysis sessions in which these symptoms occur decreases with a smaller fluid deficit.

[0008] The compartment in the body where water ingested by dialysis patients accumulates is the extracellular compartment. The compartment from which water is removed by dialysis is also the extracellular compartment. The extracellular compartment is further divided into the intravascular compartment and the interstitial compartment. Blood volume is the sum of the amount of water distributed in the intravascular compartment and the total volume of blood cells. When excess water accumulates in the extracellular compartment, the amount of water distributed in both the intravascular compartment and the interstitial compartment increases. As the amount of water distributed in the intravascular compartment increases, the blood, which consists of water and blood cells, is diluted, and blood volume increases. On the other hand, when water accumulated in the extracellular compartment is removed by dialysis, the amount of water distributed in the intravascular compartment, which is part of the extracellular fluid, decreases. As a result, the blood, which consists of water and blood cells distributed in the intravascular compartment, becomes concentrated, and blood volume decreases.

[0009] When excess water accumulates in the body, the amount of water in the interstitial compartment also increases. Edema develops when the amount of water in the interstitial compartment exceeds a certain level. The degree of edema increases in parallel with the amount of excess water accumulated in the interstitial compartment. Meanwhile, excess water accumulation in the body also increases the amount of water distributed in the central veins, located immediately upstream of the heart. As the amount of water distributed in the central veins increases, the amount of blood returning to the heart through the central veins also increases, resulting in an increase in cardiac output, or the amount of blood pumped from the heart per minute. Conversely, if the amount of water accumulated in the body decreases excessively, the amount of water distributed in the central veins also decreases. As the amount of water distributed in the central veins decreases, the amount of blood returning to the heart through the central veins also decreases, resulting in a decrease in cardiac output. When cardiac output decreases, the blood and oxygen supply to various organs decreases, resulting in organ-specific symptoms of ischemia, such as abdominal discomfort, yawning, sighing, nausea, vomiting, muscle cramps, restlessness, dizziness, loss of consciousness, and anxiety.

[0010] However, excessive water retention in the body is not the only factor that reduces the amount of water distributed to the central veins. When blood volume distributed to the liver increases, the amount of water distributed to the central veins decreases accordingly. In this case, cardiac output decreases in response to the decrease in water volume distributed to the central veins, reducing the blood and oxygen supply to various organs. This leads to the appearance of symptoms of ischemia specific to each organ, such as abdominal discomfort, yawning, sighing, nausea, vomiting, muscle cramps, restlessness, dizziness, loss of consciousness, and anxiety. Therefore, the degree of increase in blood volume distributed to the liver can be considered a factor that determines whether or not the above symptoms appear.

[0011] The mechanism by which blood volume in the liver increases begins with an excessive decrease in the amount of water retained in the body. An excessive decrease in the amount of water retained in the body reduces the total blood volume. A decrease in total blood volume also reduces the amount of blood distributed to the central veins. A decrease in the amount of blood distributed to the central veins also reduces the amount of blood returning to the heart through the central veins, resulting in a decrease in cardiac output. A decrease in cardiac output reduces the amount of blood and oxygen supplied to the liver. As a result, the liver promotes the breakdown of adenosine triphosphate (ATP), increasing the production of the vasodilator adenosine (Shinzato T, et al: Role of adenosine in dialysis-induced hypotension. J Am Soc Nephrol 4: 1987-1994,1994.). Increased adenosine production causes the vasodilatory effects of adenosine to dilate the blood vessels in the liver. When hepatic blood vessels dilate, the amount of blood distributed to the liver increases, further reducing the amount of blood in the central veins. This theory is supported by the observation that the amount of water in the liver increases in patients who experience dialysis-induced hypotension (Grant CJ, et al: Effect of ultrafiltration during hemodialysis on hepatic and total-body water: an observational study. BMC Nephrology 19: 356, 2018).

[0012] As mentioned above, the dilation of hepatic blood vessels caused by a decrease in blood and oxygen supply to the liver is due to the vasodilatory effect of adenosine. However, because adenosine degrading enzyme activity is reduced in dialysis patients, serum adenosine concentrations in dialysis patients are approximately five times higher than in healthy individuals. However, the degree of adenosine degrading enzyme activity reduction varies greatly among dialysis patients, and therefore serum adenosine concentrations also vary greatly among individuals (Guieu R, et al.: Adenosine and hemodialysis in humans. J Investig Med 49: 56-67, 2001). Furthermore, interleukin-1, a cytokine, is produced when blood comes into contact with the dialyzer membrane and is released from inflammatory sites. When hepatic venular smooth muscle cells are stimulated by interleukin-1, adenosine promotes the production of nitric oxide (NO) in hepatic venular smooth muscle cells (Ikeda U, et al.: Adenosine stimulates nitric oxide synthesis in vascular smooth muscle cells. Cardiovasc Res 35:168-174, 1997). NO has a stronger vasodilatory effect than adenosine. For these reasons, even if the degree of reduction in blood supply and oxygen supply to the liver is the same, the degree of hepatic vasodilation varies from one dialysis session to the next. Furthermore, even within the same patient and even if the degree of hepatic ischemia remains constant, the degree of hepatic vasodilation varies from session to session. In other words, if the amount of blood retained in the liver increases due to excessive fluid loss, the amount of blood increase in the liver will vary from session to session, even if the degree of fluid loss remains constant.

[0013] The body fluid volume evaluation device disclosed in this specification evaluates a dialysis patient's body fluid volume at the end of dialysis based on the following theory: If the body fluid volume at the end of dialysis decreases excessively, the blood volume in the central vein decreases. If the blood volume in the central vein decreases, cardiac output decreases. If cardiac output decreases, the blood supply and oxygen supply to the liver decrease. If the blood supply and oxygen supply to the liver decrease, the liver increases its production of adenosine, a vasodilator, thereby dilating blood vessels. As the blood vessels in the liver dilate, the blood volume distributed to the liver increases. If the blood volume distributed to the liver increases, the blood volume in the central vein decreases by the same amount. If this cycle continues, a considerable amount of blood will be distributed to the liver. If this cycle exists at the end of dialysis, the blood supply and oxygen supply to the liver increase with the return blood, causing the cycle to reverse. The excess blood distributed to the liver will move to the central vein, and cardiac output (the total amount of blood pumped by the heart per minute) will increase. Cardiac output is proportional to stroke volume, which in turn is proportional to pulse pressure (Arumugam R, et al.: Relationship between pulse pressure variation and stroke volume variation with changes in cardiac index during hypotension in patients undergoing major spine surgeries in prone position - A prospective observational study. J Anaesthesiol Clin Pharmacol. 38: 553-559, 2022.). Therefore, by examining the rate of increase in pulse pressure associated with blood return, the degree of fluid loss at the end of dialysis can be assessed.

[0014] The reason why the rate of increase in pulse pressure reflects the increase in blood volume in the liver before blood return is as follows: When dialysis is completed, the blood in the dialyzer and blood circuit is returned to the dialysis patient's body. When the blood in the dialyzer and blood circuit is returned to the dialysis patient's body at the end of dialysis, the blood volume in the dialysis patient's body increases. In this case, if the body fluid volume is not excessively reduced before blood return, the blood volume in the body is not excessively reduced, and a sufficient amount of blood and oxygen is supplied to the liver even before blood return. Therefore, the production of adenosine, which has a vasodilatory effect, does not increase in the liver. Therefore, before blood return, the blood vessels in the liver are not dilated, and the amount of blood distributed to the liver does not increase. In this state, even if the blood supply to the liver increases with blood return, the production of adenosine in the liver does not decrease. Therefore, blood does not transfer from the liver to the central vein with blood return. In other words, if there is not an excess of blood distributed to the liver, the amount of blood pumped per heartbeat (i.e., cardiac output per stroke) does not increase with blood return, nor does pulse pressure. On the other hand, if the blood volume in the body is reduced before blood return, the liver is not supplied with sufficient blood and oxygen at this point, and the liver is in an ischemic state. In an ischemic liver, the production of adenosine, which has a vasodilatory effect, increases. Therefore, the liver's blood vessels dilate, and the amount of blood distributed to the liver increases. In this state, if blood return increases the blood supply to the liver, hepatic ischemia is alleviated and adenosine production in the liver decreases. When adenosine production in the liver decreases, the liver's blood vessels constrict, thereby reducing the amount of blood distributed to the liver. When the liver's blood volume decreases, blood is transferred from the liver to the central vein to compensate for the decrease. As a result, the amount of blood returned to the heart increases, and cardiac output per stroke increases. Therefore, the rate of increase in stroke volume reflects the increase in the amount of blood distributed to the liver, and the rate of increase in pulse pressure reflects the increase in the amount of blood distributed to the liver.

[0015] Incidentally, since the stroke volume is proportional to the pulse pressure, the magnitude of the rate of increase of the stroke volume can be substituted for the magnitude of the rate of increase of the pulse pressure, and the magnitude of the variation in the rate of increase of the stroke volume can be substituted for the magnitude of the variation in the rate of increase of the pulse pressure.

[0016] The body fluid volume evaluation device disclosed herein includes a memory unit and a judgment unit. The memory unit stores the average value of the pulse pressure increase rate, an index value for the variation in pulse pressure associated with blood return, and the number of times the pulse pressure increase rate exceeds a predetermined value. The judgment unit evaluates the degree of increase in blood volume in the liver before blood return based on these values ​​and further estimates the excess or deficiency of body fluid volume corresponding to the degree of increase in blood volume in the liver. That is, when the average value of the pulse pressure increase rate is higher than a predetermined first value, the judgment unit determines that excess blood is accumulated in the liver and therefore the body fluid volume is insufficient. On the other hand, when the average value of the pulse pressure increase rate is lower than a predetermined second value, the judgment unit determines that excess blood is not accumulated in the liver and therefore the body fluid volume is excessive. Note that the first value is higher than the second value. On the other hand, when the average value of the pulse pressure increase rate is lower than the predetermined first value and higher than the predetermined second value, the judgment unit determines that an appropriate amount of blood is accumulated in the liver and therefore the body fluid volume is appropriate. When the standard deviation, which is an index of variation, is lower than a third preset value, it is determined that there is no excess blood in the liver, and therefore the body fluid volume is excessive.Furthermore, when the number of times that the rate of increase in pulse pressure exceeds a preset value is greater than a fourth preset value (number of times), it is determined that there is excess blood in the liver, and therefore the body fluid volume is insufficient.

[0017] The body fluid volume evaluation device determines the degree of hepatic blood volume increase based on the average value of the pulse pressure increase rate over multiple dialysis sessions, the degree of variation in the pulse pressure increase rate over multiple dialysis sessions, and the number of times the pulse pressure increase rate exceeded a predetermined value over multiple dialysis sessions, and evaluates the excess or deficiency of body fluid volume corresponding to the degree of hepatic blood volume increase. Therefore, this body fluid volume evaluation device can accurately determine the excess or deficiency of body fluid volume in a dialysis patient. Hereinafter, the average value of the pulse pressure increase rate over multiple dialysis sessions will be referred to as the average pulse pressure increase rate, and the variation in the pulse pressure increase rate over multiple dialysis sessions will be referred to as the pulse pressure increase rate variation.

[0018] This specification also discloses a computer program for evaluating the body fluid volume of a dialysis patient at the end of dialysis. The computer program causes a computer to function as a pulse pressure acquisition unit, a first calculation unit, a second calculation unit, and an evaluation unit. The pulse pressure acquisition unit acquires a first pulse pressure, which is the pulse pressure of the dialysis patient at the end of dialysis before blood in the dialyzer and blood circuit is returned to the body of the dialysis patient, and a second pulse pressure, which is the pulse pressure of the dialysis patient at the end of blood return. The pulse pressure acquisition unit acquires the first pulse pressure and the second pulse pressure over multiple consecutive dialysis sessions of the dialysis patient. The first calculation unit calculates an increase rate of the pulse pressure from the first pulse pressure and the second pulse pressure. The first calculation unit calculates an increase rate of the pulse pressure for each of the multiple dialysis sessions from the first pulse pressure and the second pulse pressure. The second calculation unit calculates at least one of an index indicating the average value and a variation of the increase rate of the pulse pressure over the multiple dialysis sessions calculated by the first calculation unit. The evaluation unit evaluates the body fluid volume of the dialysis patient based on at least one of the average value and the index indicating the variation calculated by the second calculation unit.

[0019] Graph showing heart rate at the start of blood return and heart rate at the end of blood return. Graph showing the rate of increase in pulse pressure over multiple consecutive dialysis sessions, where (a) shows a patient in an overhydrated state, (b) shows a patient in an appropriate state (a patient who is neither overhydrated nor dehydrated), and (c) shows a patient in a dehydrated state. Graph showing the distribution of the average and standard deviation values ​​of the rate of increase in pulse pressure over multiple sessions in an overhydrated state, an appropriate state, and a dehydrated state, where (a) shows the distribution of the average values, and (b) shows the distribution of the standard deviation values. Block diagram showing the schematic configuration of a body fluid volume evaluation device according to an embodiment. Flowchart showing an example of a process for evaluating the hydration status of a dialysis patient at the end of dialysis.

[0020] The main features of the embodiments described below are listed below. Note that the technical elements described below are independent technical elements that exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0021] In the technology disclosed in this specification, the body fluid volume evaluation device may include a memory unit. The memory unit may store a first value that is a boundary between the average value of the pulse pressure increase rate when the dialysis patient's body fluid volume is excessive and the average value of the pulse pressure increase rate when the dialysis patient's body fluid volume is appropriate. The memory unit may also store a second value that is a boundary between the average value of the pulse pressure increase rate when the dialysis patient's body fluid volume is appropriate and the average value of the pulse pressure increase rate when the dialysis patient's body fluid volume is insufficient. With this configuration, if the average value of the pulse pressure increase rate is greater than the first value stored in the memory unit, it is possible to determine that the dialysis patient's liver blood volume has increased excessively at the end of dialysis, and therefore that the body fluid volume is insufficient. On the other hand, if the average value of the pulse pressure increase rate is smaller than the second value stored in the memory unit, it is possible to determine that the dialysis patient's liver blood volume has not increased at the end of dialysis, and therefore that the body fluid volume is excessive.

[0022] In the technology disclosed in this specification, the body fluid volume evaluation device may further include a memory unit that stores a third value that is a threshold value for an index of variation in the rate of increase of pulse pressure. With this configuration, if the index of variation in the rate of increase of pulse pressure is smaller than the third value that is the threshold value (upper limit value) for the index of variation in the rate of increase of pulse pressure stored in the memory unit, it can be determined that the blood volume in the liver of the dialysis patient has not increased at the end of dialysis, and therefore the body fluid volume is excessive.

[0023] In the technology disclosed in this specification, the index indicating the variation may be a standard deviation value.

[0024] In the technology disclosed in this specification, the body fluid volume evaluation device may further include a memory unit. The memory unit may store a fourth value that is an upper limit for the percentage of dialysis sessions in which the increase rate of pulse pressure was higher than a predetermined value. The memory unit may also store a fifth value that is a lower limit for the percentage of dialysis sessions in which the increase rate of pulse pressure was higher than a predetermined value. With this configuration, if the percentage of dialysis sessions in which the increase rate of pulse pressure was higher than a predetermined value is higher than the fourth value, it can be determined that the frequency of dialysis sessions in which the hepatic blood volume increased excessively at the end of dialysis was high, and therefore the body fluid volume is insufficient. On the other hand, if the percentage of dialysis sessions in which the increase rate of pulse pressure was higher than a predetermined value is lower than the fifth value, it can be determined that the frequency of dialysis sessions in which the hepatic blood volume increased excessively was low, and therefore the body fluid volume is not insufficient or is excessive.

[0025] In a second aspect of the technology disclosed in this specification, in the first aspect described above, the body fluid volume evaluation device may further include a memory unit that stores a threshold value of the average value when the dialysis patient's body is in a dehydrated state at the end of dialysis.

[0026] In a third aspect of the technology disclosed in this specification, in the first or second aspect described above, the body fluid volume evaluation device may further include a memory unit that stores a threshold value of the variation index when the dialysis patient's body is in a state of overflow at the end of dialysis.

[0027] In a fourth aspect of the technology disclosed in this specification, in any one of the first to third aspects above, the memory unit may further store a threshold value of the average value when the dialysis patient's body is in a state of overflowing water at the end of dialysis.

[0028] In a fifth aspect of the technology disclosed in the present specification, in any one of the first to fourth aspects, the index indicating the variation may be a standard deviation.

[0029] In a sixth aspect of the technology disclosed in this specification, in the first aspect, the body fluid volume evaluation device may further include a memory unit that stores a first value that is a threshold value of the average value when the dialysis patient's body is dehydrated at the end of dialysis, a second value that is a threshold value of the average value when the dialysis patient's body is overhydrated at the end of dialysis, and a third value that is a threshold value of the index of variation when the dialysis patient's body is overhydrated at the end of dialysis. The evaluation unit may determine that the dialysis patient is dehydrated when the average value is equal to or greater than the first value, determine that the dialysis patient is overhydrated when the average value is equal to or less than the second value and the index of variation is equal to or less than the third value, and determine that the dialysis patient is neither overhydrated nor dehydrated when the average value is greater than the second value and less than the first value, or when the average value is equal to or less than the second value and the index of variation exceeds the third value.

[0030] A body fluid volume evaluation device 10 according to this embodiment will be described with reference to the drawings. The body fluid volume evaluation device 10 evaluates whether the blood volume in the liver of a dialysis patient has increased at the end of dialysis based on the rate of increase in pulse pressure associated with the blood return operation performed at the end of dialysis. Evaluating the blood volume in the liver of a dialysis patient at the end of dialysis indirectly evaluates the blood volume in the central vein of the dialysis patient at the end of dialysis, and further evaluates the body fluid volume of the patient.

[0031] First, we will explain the central venous blood volume of a dialysis patient at the end of dialysis. As mentioned above, a decrease in body fluid volume leads to a decrease in central venous blood volume. A decrease in central venous blood volume reduces cardiac return. A decrease in cardiac return reduces cardiac output. A decrease in cardiac output reduces blood and oxygen supply to the liver. Furthermore, a decrease in blood and oxygen supply to the liver accelerates the breakdown of adenosine triphosphate (ATP) in the liver, resulting in the release of adenosine. Adenosine is also known as a vasodilator. Increased release of adenosine dilates hepatic blood vessels, increasing the amount of blood distributed to the liver. This further reduces central venous blood volume and ultimately leads to dialysis hypotension (Shinzato T, et al.: Role of adenosine in dialysis-induced hypotension. J Am Soc Nephrol 4: 1987-1994, 1994). On the other hand, if the body fluid volume does not decrease or if it actually increases, the blood volume in the central vein does not decrease, but rather increases. If the blood volume in the central vein does not decrease, but rather increases, the cardiac blood return volume does not decrease, but rather increases. If the cardiac blood return volume does not decrease, but rather increases, cardiac output does not decrease, but rather increases. If the cardiac output does not decrease, but rather increases, the blood supply and oxygen supply to the liver do not decrease, but rather increase. If the blood supply and oxygen supply to the liver do not decrease, but rather increase, the breakdown of ATP in the liver does not promote, and the release of adenosine does not increase. If the release of adenosine does not increase, the blood vessels in the liver do not dilate, and the amount of blood distributed to the liver does not increase. If the amount of blood distributed to the liver does not increase, the blood volume in the central vein does not decrease, and therefore symptoms such as dialysis hypotension do not occur.

[0032] Whether or not the amount of blood distributed to the liver is increasing due to a decrease in the blood supply and oxygen supply to the liver can be confirmed by administering a small amount of fluid replacement. When the blood supply and oxygen supply to the liver are decreased, the following cycle occurs: the blood supply and oxygen supply to the liver decrease, then adenosine production in the liver increases, then the amount of blood distributed to the liver increases, then the blood volume in the central vein decreases, then the cardiac blood return decreases, then the cardiac output decreases, and then the blood supply and oxygen supply to the liver decrease again. This cycle repeats. When this cycle is occurring, if approximately 200 mL of saline is added, the cycle will reverse as follows: That is, when a small amount of fluid, about 200 mL, is administered, the blood supply and oxygen supply to the liver increase slightly, then adenosine production in the liver decreases slightly, then the blood volume distributed to the liver decreases slightly, then the blood volume in the central vein increases slightly, then the blood return to the heart increases slightly, then the cardiac output increases slightly, then the blood supply and oxygen supply to the liver increase slightly, then the blood volume in the liver decreases slightly, then the blood volume in the central vein increases slightly, then the cardiac output increases slightly. This cycle is repeated, and finally the cardiac output increases significantly.

[0033] After dialysis, approximately 200 mL of blood circulating through the dialyzer and blood circuit of the dialysis machine must be returned to the body. Hereinafter, the process of returning blood circulating through the dialyzer and blood circuit to the body is referred to as "blood return." The time before blood return at the end of dialysis is referred to as "before blood return," and the time after blood return is referred to as "after blood return." Blood return is a special form of fluid replacement. Therefore, if the blood supply and oxygen supply to the liver are reduced, increasing the amount of blood distributed to the liver and thus decreasing the blood volume in the central vein, blood return increases cardiac output. On the other hand, if the blood volume distributed to the liver is not increased and therefore the blood volume in the central vein is not decreased, blood return does not increase cardiac output. Therefore, by examining whether or not cardiac output increases with blood return, it is possible to determine whether or not the blood volume distributed to the liver has increased. In other words, it is possible to determine whether or not the body fluid volume was excessive or insufficient.

[0034] Cardiac output is the total volume of blood pumped per minute by one contraction of the heart. In other words, cardiac output is the product of stroke volume and heart rate per minute. In an experiment conducted on 65 patients (see Figure 1), the heart rate per minute before blood transfusion was 73.2 ± 15.9 beats / min, while the heart rate per minute after blood transfusion was 73.1 ± 14.5 beats / min, with no significant difference. That is, the heart rate remains unchanged before and after blood transfusion. Therefore, the rate of increase in cardiac output is equal to the rate of increase in stroke volume. Furthermore, since stroke volume is proportional to pulse pressure, the rate of increase in stroke volume is equal to the rate of increase in pulse pressure. Therefore, by examining whether pulse pressure increases after blood transfusion, we can evaluate whether the blood volume in the liver has increased, thereby determining whether the body fluid volume was excessive or insufficient.

[0035] A method for evaluating the degree of increase in blood volume distributed to the liver at the end of dialysis will be described in more detail. If the dialysis patient's internal blood volume is lower than the appropriate volume before blood return, even if the internal blood volume does not fluctuate, the amount of blood stored in the liver will fluctuate from one dialysis session to another due to factors such as differences in water removal rate and changes in physical condition. That is, even if the dialysis patient's body fluid volume does not fluctuate, the amount of blood distributed to the liver will differ from one dialysis session to another. Therefore, using the rate of increase in stroke cardiac output before and after blood return obtained in a single dialysis session may not accurately evaluate whether the dialysis patient's body fluid volume at the end of dialysis is lower than the appropriate volume. For example, if the dialysis patient's internal blood volume is lower than the appropriate volume and the amount of blood distributed to the liver is increased, the rate of increase in stroke cardiac output before and after blood return will be large. Therefore, it is possible to evaluate that the dialysis patient's body fluid volume at the end of dialysis is lower than the appropriate volume. On the other hand, if the dialysis patient's internal blood volume is lower than the appropriate volume but the amount of blood distributed to the liver is small, the rate of increase in stroke cardiac output before and after blood return will not be very large. In this case, the amount of body fluid in the dialysis patient at the end of dialysis may not be evaluated as being less than the appropriate amount.

[0036] Therefore, in this embodiment, whether the amount of blood distributed to the liver of a dialysis patient has increased at the end of dialysis is evaluated based on the multiple increase rates of pulse pressure before and after blood return obtained over multiple dialysis sessions. Here, "multiple dialysis sessions" refers to multiple consecutive dialysis sessions. Furthermore, in multiple consecutive dialysis sessions, dialysis is performed under the same conditions (e.g., the same dry weight). Even if the patient's body fluid and blood volumes are lower than the appropriate volume in all of the multiple dialysis sessions, the increase rates of pulse pressure before and after blood return in the multiple dialysis sessions may include some large and some not so large. This is because the amount of blood distributed to the liver varies for each dialysis session. However, for example, if the patient's body fluid and blood volumes are lower than the appropriate volume in all of the multiple dialysis sessions, averaging the increase rates of pulse pressure before and after blood return in the multiple dialysis sessions will result in a sufficiently high average value. In other words, by using the average value of the multiple increase rates of pulse pressure before and after blood return obtained over multiple dialysis sessions, the body fluid volume of a dialysis patient at the end of dialysis can be accurately evaluated.

[0037] The average value of the rate of increase in pulse pressure associated with blood return over multiple dialysis sessions (hereinafter simply referred to as the "average rate of increase in pulse pressure") can be used to determine the dry weight for the next dialysis session. Specifically, if the average rate of increase in pulse pressure is higher than the upper threshold, the dry weight for the next dialysis session is set higher than the dry weight for the current dialysis session. On the other hand, if the average rate of increase in pulse pressure is lower than the lower threshold, the dry weight for the next dialysis session is set lower than the dry weight for the current dialysis session. Furthermore, if the average rate of increase in pulse pressure is lower than the upper threshold and higher than the lower threshold, the dry weight for the next dialysis session is set the same as the dry weight for the current dialysis session.

[0038] The rate of increase in stroke volume is expressed by the following formula 1. Here, Ra indicates the rate of increase in stroke volume before and after blood return, SV0 indicates the stroke volume before blood return, and SV1 indicates the stroke volume after blood return.

[0039]

[0040] Stroke volume can be calculated by dividing cardiac output measured directly using, for example, thermodilution by heart rate. However, calculating stroke volume by dividing cardiac output measured directly using thermodilution by heart rate places a significant burden on medical professionals performing the thermodilution measurement and on the dialysis patient. Therefore, in this embodiment, pulse pressure, which is easily measurable and proportional to stroke volume, is used instead of stroke volume. Pulse pressure is the difference between systolic and diastolic blood pressure and may be measured with a sphygmomanometer. In this embodiment, the rate of increase in pulse pressure before and after blood return is used to evaluate whether the amount of blood distributed to the dialysis patient's liver has increased at the end of dialysis, thereby evaluating whether the dialysis patient's body fluid volume at the end of dialysis is appropriate.

[0041] As mentioned above, pulse pressure is proportional to stroke volume. Therefore, the rate of increase in pulse pressure before and after blood return can be expressed by the following equation 2. Ra indicates the rate of increase in pulse pressure before and after blood return, PP0 indicates the pulse pressure before blood return, and PP1 indicates the pulse pressure after blood return.

[0042]

[0043] By obtaining the pulse pressure before and after blood return, the rate of increase in pulse pressure before and after blood return (hereinafter simply referred to as the "rate of increase in pulse pressure") can be calculated using the above formula 2. By obtaining the rate of increase in pulse pressure, it is possible to evaluate whether the amount of blood distributed to the liver of a dialysis patient at the end of dialysis has increased, and thereby evaluate whether the amount of body fluid in the dialysis patient at the end of dialysis is appropriate.

[0044] When measured with a sphygmomanometer, pulse pressure is the difference between systolic blood pressure and diastolic blood pressure. Therefore, the rate of increase in pulse pressure can also be expressed by the following equation (3). Note that BPs0 indicates the systolic blood pressure at the start of blood return, BPd0 indicates the diastolic blood pressure at the start of blood return, BPs1 indicates the systolic blood pressure at the end of blood return, and BPd1 indicates the diastolic blood pressure at the end of blood return.

[0045]

[0046] Figures 2(a) to 2(c) show the rate of increase in pulse pressure over six consecutive dialysis sessions for a dialysis patient. Each of Figures 2(a) to 2(c) shows the change in the rate of increase in pulse pressure for one patient. Figure 2(a) shows a patient who exhibited symptoms of overflow (edema) (hereinafter simply referred to as a "patient with overflow"); Figure 2(b) shows a patient who did not exhibit symptoms of overflow and did not experience dialysis hypotension; and Figure 2(c) shows a patient who experienced dialysis hypotension (hereinafter also referred to as a "patient with dehydration"). Note that the patient in Figure 2(b) who did not exhibit symptoms of overflow and did not experience dialysis hypotension does not require dry weight resetting, and therefore, for ease of explanation, will be referred to as a "patient with an appropriate body fluid volume" below. In Figures 2(a) to 2(c), the dashed line indicates 0%, and the solid line A parallel to the dashed line indicates the average rate of increase in pulse pressure over six consecutive dialysis sessions.

[0047] As shown in Figure 2(a), in a patient with overflow, the rate of increase in pulse pressure fluctuated within a narrow range around 0% over the six dialysis sessions. As mentioned above, if the body's internal blood volume before blood return is large, the rate of increase in stroke volume before and after blood return is small. This is because a large body fluid volume before blood return increases the body's internal blood volume, which does not decrease the amount of blood and oxygen supplied to the liver. Therefore, the amount of blood distributed to the liver does not increase, and therefore, stroke volume does not increase even after blood return. Incidentally, stroke volume is proportional to pulse pressure. Therefore, in a patient with overflow, the rate of increase in pulse pressure before and after blood return fluctuated within a narrow range around 0%. Note that in Figure 2(a), the rate of increase in pulse pressure is negative in the second dialysis session. Physiologically, the rate of increase in pulse pressure cannot be negative. However, pulse pressure is calculated as the difference between systolic and diastolic blood pressures measured with a conventional cuff-type sphygmomanometer, so measurement errors can occur in pulse pressure. The negative pulse pressure increase rate in the second dialysis session can be attributed to measurement error. Furthermore, in patients with overflow, the pulse pressure increase rates for all six sessions were approximately 0%, so the standard deviation was also approximately 0%. In summary, in patients with overflow, the average pulse pressure increase rate over multiple dialysis sessions is small, and the standard deviation is also small. In other words, if the average pulse pressure increase rate is small and the standard deviation is also small, the dialysis patient's body fluid volume state can be determined to be overflow.

[0048] As shown in Figure 2(b), in patients with an appropriate body fluid volume (patients who did not show symptoms of overflow and did not experience dialysis hypotension), the increase rate of pulse pressure over six dialysis sessions varied widely, but the average was approximately 0%. Therefore, in patients with an appropriate body fluid volume, the average increase rate of pulse pressure over multiple dialysis sessions is small and the standard deviation is large. In other words, if the average increase rate of pulse pressure is small and the standard deviation is large, it can be determined that the dialysis patient's body fluid volume is neither overflowing nor dehydrated.

[0049] As shown in Figure 2(c), in dehydrated patients, the pulse pressure increase rate varied widely over the six dialysis sessions, and the average pulse pressure increase rate was approximately 20%, much higher than 0%. This phenomenon is thought to be due to the following reasons: In dehydrated patients, the blood volume in the body before blood return is low, resulting in a reduced cardiac output. A decrease in cardiac output reduces the blood and oxygen supply to the liver, leading to increased production of adenosine, which has a vasodilatory effect. Incidentally, adenosine promotes the production of NO, a compound with a stronger vasodilatory effect than adenosine, in smooth muscle cells of hepatic venules stimulated with interleukin-1 (Ikeda U, et al.: Adenosine stimulates nitric oxide synthesis in vascular smooth muscle cells. Cardiovasc Res 35:168-174, 1997). However, the production rate of interleukin-1 varies depending on many factors, including inflammation, contact of blood monocytes with the dialyzer membrane, endotoxin concentration in the dialyzer fluid, and blood flow rate within the dialyzer (Henderson LW, et al.: Hemodialysis hypotension: The interleukin-1 hypothesis. Blood Purif 1: 3-8, 1983). Therefore, when blood and oxygen supply to the liver are reduced, the liver's blood vessels dilate, increasing the amount of blood distributed to the liver, but the degree of this dilation varies from session to session. As a result, even if the patient's body fluid volume remains constant, the amount of blood distributed to the liver varies from session to session, resulting in variations in the rate of increase in stroke volume. Therefore, in dehydrated patients, the mean increase in pulse pressure over multiple dialysis sessions and the standard deviation are large. In other words, a large mean increase in pulse pressure and a large standard deviation indicate that a dialysis patient is dehydrated.

[0050] Next, we will explain the upper and lower thresholds used to determine whether a dialysis patient's body fluid volume state is overhydrated, dehydrated, or neither overhydrated nor dehydrated (for ease of explanation, this may be referred to as an "optimal state") based on the average and standard deviation of the pulse pressure increase rate over multiple dialysis sessions. The upper and lower thresholds for the average pulse pressure increase rate are common to all patients. This is for the following reason: When the degree of dehydration is the same, the amount of excess blood stored in the liver is greater for larger patients and less for smaller patients. Therefore, an index of the degree of dehydration common to all patients is the amount of excess blood stored in the liver corrected for body size. Meanwhile, the "rate of increase in stroke volume due to blood reinfusion" is calculated by dividing the "amount of increase in stroke volume due to blood reinfusion" by the stroke volume before blood reinfusion, i.e., the value corrected by the stroke volume before blood reinfusion. The stroke volume before blood return is higher in larger patients and lower in smaller patients. Therefore, the "rate of increase in stroke volume with blood return" is an index obtained by correcting the "amount of increase in stroke volume with blood return" with an index of body size. Incidentally, the "amount of increase in stroke volume with blood return" indicates the amount of excess blood pooling in the liver. From the above, it can be seen that the rate of increase in stroke volume with blood return is an index indicating the degree of dehydration. Therefore, the upper and lower thresholds indicating the average rate of increase in pulse pressure depend solely on the degree of dehydration, not on the patient's physical size. In other words, the upper and lower thresholds indicating the average rate of increase in pulse pressure are common to all patients. Note that the various thresholds described below are merely examples, and each threshold can be set using a method similar to that described below; the specific values ​​of each threshold are not limited.

[0051] Twenty-four dialysis patients were divided into an overflow group (6 patients), an adequate group (11 patients), and a dehydrated group (7 patients). The overflow group consisted of patients who exhibited symptoms of overflow, such as edema. The adequate group consisted of patients who did not exhibit symptoms of overflow and did not experience dialysis-related hypotension (i.e., patients with adequate hydration or patients who were not clearly overflowed or dehydrated). The dehydrated group consisted of patients who experienced dialysis-related hypotension. For all 24 dialysis patients, systolic and diastolic blood pressures were measured before and after blood reinfusion using a cuff-type sphygmomanometer (a sphygmomanometer that first measures systolic blood pressure, then diastolic blood pressure) on the arm without blood access. The systolic and diastolic blood pressures before and after blood reinfusion were substituted into the equation shown above (3) to calculate the rate of increase in pulse pressure. The pulse pressure was measured before and after blood reinfusion in six consecutive dialysis sessions, and the rate of increase in pulse pressure was calculated for each dialysis session.The mean and standard deviation were then calculated from the six calculated rates of increase in pulse pressure.

[0052] As shown in Figures 3(a) and 3(b), in the overflow group, the average increase rate of pulse pressure was 6% or less, and the standard deviation was 6%. All patients in the overflow group and several patients in the appropriate group had an average increase rate of pulse pressure of 6% or less. The average increase rate of pulse pressure alone did not clearly distinguish between the overflow group and the appropriate group. However, only the overflow group had a standard deviation of 6% or less, while the appropriate and dehydrated groups had standard deviations higher than 6%. Therefore, if the average increase rate of pulse pressure over multiple consecutive dialysis sessions is 6% or less and the standard deviation is 6%, the hydration status of a dialysis patient can be determined to be overflowing.

[0053] In addition, the average increase rate of pulse pressure in the dehydrated group was 15% or more. In addition to all of the dehydrated group, one patient in the appropriate group also had an average increase rate of pulse pressure of 15% or more, but this one patient in the appropriate group can be considered within the margin of error. Therefore, if the average increase rate of pulse pressure over multiple consecutive dialysis sessions is 15% or more, the dialysis patient's internal fluid status can be determined to be dehydrated.

[0054] If none of the above conditions are met, the condition can be determined to be appropriate. As mentioned above, the "appropriate condition" here means that the patient is neither overhydrated nor dehydrated, and does not necessarily mean that the amount of fluid in the body of the dialysis patient is appropriate. Specifically, if the average value of the rate of increase in pulse pressure over multiple consecutive dialysis sessions is more than 6% and less than 15%, or if the average value of the rate of increase in pulse pressure is 6% or less and the standard deviation is more than 6%, the condition can be determined to be appropriate (neither overhydrated nor dehydrated).

[0055] Next, the configuration of the body fluid volume evaluation device 10 will be described. The body fluid volume evaluation device 10 includes a calculation unit 12, an input unit 22, and a display unit 24. The calculation unit 12 can be configured, for example, by a computer including a CPU, ROM, RAM, etc. The calculation unit 12 is connected to the input unit 22 and the display unit 24.

[0056] The calculation unit 12 includes a bodily fluid volume evaluation unit 14 and a determination unit 20. The bodily fluid volume evaluation unit 14 includes a memory unit 16 and a calculation unit 18. The memory unit 16 stores the pulse pressure before and after blood return obtained from the input unit 22. The memory unit 16 also stores the pulse pressure increase rates for the most recent several dialysis sessions (in this embodiment, the most recent five sessions) obtained from the input unit 22. As described above, the pulse pressure increase rates stored in the memory unit 16 are the pulse pressure increase rates for the most recent several dialysis sessions performed under the same conditions (e.g., dry weight). The memory unit 16 may also store the pulse pressure before and after blood return for the most recent several dialysis sessions (performed under the same conditions). The memory unit 16 also stores the pulse pressure increase rates (or the pulse pressure before and after blood return) for multiple dialysis sessions for each patient. The calculation unit 18 calculates the rate of increase in pulse pressure from the pulse pressure before and after blood return stored in the memory unit 16. The calculation unit 18 also calculates the average value and standard deviation of the rate of increase in pulse pressure for each of multiple dialysis sessions. The judgment unit 20 judges the hydration state of the dialysis patient at the end of dialysis from the average value and standard deviation of the rate of increase in pulse pressure for multiple dialysis sessions calculated by the calculation unit 18.

[0057] The input unit 22 receives instructions and information from the operator. For example, the input unit 22 receives input of the pulse pressure before and after blood return, and the rate of increase in pulse pressure over the most recent several dialysis sessions. The input unit 22 may also receive input of the pulse pressure before and after blood return over multiple dialysis sessions. The input information is output from the input unit 22 to the calculation unit 12. The display unit 24 displays the determination result of the determination unit 20 on the hydration state of the dialysis patient at the end of dialysis. The display unit 24 may also display the average value and standard deviation of the rate of increase in pulse pressure over multiple dialysis sessions calculated by the calculation unit 18.

[0058] Next, we will explain the process of evaluating the hydration status of a dialysis patient at the end of dialysis using the body fluid volume evaluation device 10. In this example, the body fluid volume evaluation device 10 uses the pulse pressure before and after blood return in six consecutive dialysis sessions (performed under the same conditions) to calculate the average and standard deviation of the pulse pressure increase rate and determine the hydration status of the dialysis patient at the end of dialysis. In this example, the pulse pressure increase rates for the most recent five dialysis sessions are stored in the memory unit 16, and the following process is performed after the sixth dialysis session is completed.

[0059] First, the calculation unit 12 acquires the pulse pressure before and after blood return for the current (sixth) dialysis session via the input unit 22 (S12). The pulse pressure before blood return is measured before blood is returned at the end of dialysis. The pulse pressure after blood return is measured at the end of blood return. The pulse pressure before and after blood return are measured using a measuring device such as a cuff-type blood pressure monitor or pulse oximeter. The calculation unit 12 stores the acquired pulse pressure before and after blood return in the memory unit 16.

[0060] Next, the calculation unit 18 calculates the rate of increase in the pulse pressure in the current (sixth) dialysis session from the pulse pressure before and after blood return obtained in step S12 (S14). Specifically, the calculation unit 18 calculates the rate of increase in the pulse pressure using the above-mentioned formula 2 or 3.

[0061] Next, the calculation unit 18 acquires the increase rates of the pulse pressure for the most recent five dialysis sessions stored in the memory unit 16 (S16). Note that the calculation unit 18 may acquire the pulse pressure before and after blood return for the most recent five dialysis sessions and calculate the increase rates of the pulse pressure for each of the most recent five dialysis sessions.

[0062] Next, the calculation unit 18 calculates the average value and standard deviation of the pulse pressure increase rate over six consecutive dialysis sessions using the pulse pressure increase rate calculated in step S14 and the pulse pressure increase rates over the most recent five dialysis sessions obtained in step S16 (S18).

[0063] Next, the judgment unit 20 determines whether the average value calculated in step S18 is 6% or less (S20). As described above, if the average value of the increase rate of pulse pressure over multiple consecutive dialysis sessions is 6% or less, the dialysis patient's internal hydration status can be determined to be in an over-hydration state or an appropriate state. If the average value is 6% or less (YES in step S20), the judgment unit 20 determines whether the standard deviation value calculated in step S18 is 6% or less (S22). As described above, if the average value of the increase rate of pulse pressure over multiple consecutive dialysis sessions is 6% or less and the standard deviation value is 6% or less, the dialysis patient's internal hydration status can be determined to be in an over-hydration state. If the standard deviation value is 6% or less (YES in S22), the judgment unit 20 determines that the dialysis patient's internal hydration status is in an over-hydration state (S24). Then, the calculation unit 12 causes the display unit 24 to display an indication that the dialysis patient is in an over-hydration state (S26).

[0064] On the other hand, as described above, if the average increase rate of pulse pressure over multiple consecutive dialysis sessions is 6% or less and the standard deviation is greater than 6%, the hydration status of the dialysis patient can be determined to be appropriate. If the standard deviation exceeds 6% (NO in S22), the judgment unit 20 determines that the hydration status of the dialysis patient is appropriate (S30). The calculation unit 12 then displays on the display unit 24 that the hydration status is appropriate (i.e., the patient is neither overhydrated nor dehydrated) (S32).

[0065] If the average value exceeds 6% (NO in step S20), the judgment unit 20 judges whether the average value is 15% or greater (S28). As described above, if the average value of the pulse pressure increase rate over multiple consecutive dialysis sessions is 15% or greater, the dialysis patient's internal fluid status can be determined to be dehydrated. If the average value is 15% or greater (YES in S28), the judgment unit 20 judges the dialysis patient's internal fluid status to be dehydrated (S34). The calculation unit 12 then causes the display unit 24 to display a message indicating dehydration (S36).

[0066] On the other hand, if the average value does not exceed 15% (NO in step S28), the average value is greater than 6% (NO in step S20) and less than 15%. As described above, if the average value of the increase rate of pulse pressure over multiple consecutive dialysis sessions is less than 6% and the standard deviation is greater than 6%, the dialysis patient's internal hydration status can be determined to be appropriate. Therefore, the judgment unit 20 determines that the dialysis patient's internal hydration status is appropriate (S30), and the calculation unit 12 displays on the display unit 24 that the status is appropriate (i.e., the patient is neither clearly overhydrated nor dehydrated) (S32).

[0067] In this embodiment, the dialysis patient's internal hydration status is determined to be overhydrated when the average increase rate of pulse pressure over multiple consecutive dialysis sessions is 6% or less and the standard deviation is 6% or less. However, this configuration is not limited to this. As described above, the standard deviation is 6% or less in the overhydrated state and exceeds 6% in the normal state and the dehydrated state (see FIG. 2(b)). Therefore, the judgment unit 20 may determine that the internal hydration status of a dialysis patient is overhydrated when the standard deviation is 6% or less, without taking the average value into consideration.

[0068] In this embodiment, the hydration status of a dialysis patient at the end of dialysis was evaluated using the rate of increase in pulse pressure over six consecutive dialysis sessions. However, this configuration is not limited to this. For example, the hydration status of a dialysis patient at the end of dialysis may be evaluated based on the rate of increase in pulse pressure over three to twelve consecutive dialysis sessions. By using the rate of increase in pulse pressure over three or more consecutive dialysis sessions, the hydration status of a dialysis patient can be adequately evaluated, even if the amount of blood stored in the liver varies with each dialysis session. Furthermore, by using the rate of increase in pulse pressure over 12 or fewer consecutive dialysis sessions, it is possible to avoid an excessively long period between the first and final sessions (up to the 12th session). If the period between the first and final sessions is too long, the dialysis patient's body shape may change, potentially altering the appropriate dry weight. Since 12 consecutive dialysis sessions are often performed over approximately one month, the hydration status of a dialysis patient is unlikely to change significantly. Therefore, it is preferable to evaluate the hydration status of a dialysis patient at the end of dialysis using the rate of increase in pulse pressure over three to 12 consecutive dialysis sessions.

[0069] Furthermore, in this embodiment, the standard deviation of the rate of increase in pulse pressure over multiple consecutive dialysis sessions was calculated, but this configuration is not limited to this. It is sufficient to be able to show the variation in the rate of increase in pulse pressure over multiple consecutive dialysis sessions. For example, the variance of the rate of increase in pulse pressure over multiple consecutive dialysis sessions may be calculated. Furthermore, in this embodiment, the body fluid volume evaluation unit 14 is provided in the body fluid volume evaluation device 10, but this configuration is not limited to this. For example, the body fluid volume evaluation unit 14 may be provided in a PC separate from the PC in which the determination unit 20 is provided.

[0070] Points to note regarding the body fluid volume evaluation device 10 described in the examples will be described below. The body fluid volume evaluation unit 14 in the examples is an example of an "evaluation unit," the calculation unit 18 is an example of a "first calculation unit" and a "second calculation unit," and the input unit 22 is an example of a "pulse pressure acquisition unit."

[0071] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of those objectives itself has technical utility.

Claims

1. A device for evaluating the body fluid volume of a dialysis patient at the end of dialysis, comprising: a pulse pressure acquisition unit that acquires a first pulse pressure, which is the pulse pressure of the dialysis patient at the end of dialysis before the blood in the dialyzer and blood circuit is returned to the body of the dialysis patient, and a second pulse pressure, which is the pulse pressure of the dialysis patient at the end of blood return, the pulse pressure acquisition unit acquiring the first pulse pressure and the second pulse pressure over multiple consecutive dialysis sessions of the dialysis patient; a first calculation unit that calculates an increase rate of the pulse pressure from the first pulse pressure and the second pulse pressure, the first calculation unit calculating the increase rate of the pulse pressure for each of the multiple dialysis sessions from the first pulse pressure and the second pulse pressure of each of the multiple dialysis sessions; a second calculation unit that calculates at least one of an index indicating an average value and a variation of the increase rate of the pulse pressure over the multiple dialysis sessions calculated by the first calculation unit; and an evaluation unit that evaluates the body fluid volume of the dialysis patient based on at least one of the indexes indicating the average value and the variation calculated by the second calculation unit.

2. The body fluid volume evaluation device according to claim 1, further comprising a memory unit for storing a threshold value of the average value when the dialysis patient is in a dehydrated state at the end of dialysis.

3. The body fluid volume evaluation device according to claim 1, further comprising a memory unit for storing a threshold value of the index of said variation when the body of a dialysis patient is in an overflowing state at the end of dialysis.

4. The body fluid volume evaluation device according to claim 3, wherein the memory unit further stores a threshold value of the average value when the dialysis patient's body is in an overflowing state at the end of dialysis.

5. The body fluid volume evaluation device according to claim 1, wherein the index indicating the variation is a standard deviation.

6. A body fluid volume evaluation device as described in claim 1, further comprising a memory unit that stores a first value that is a threshold value of the average value when the dialysis patient's body is dehydrated at the end of dialysis, a second value that is a threshold value of the average value when the dialysis patient's body is overhydrated at the end of dialysis, and a third value that is a threshold value of the index of variation when the dialysis patient's body is overhydrated at the end of dialysis, wherein the evaluation unit determines that the dialysis patient's body is dehydrated when the average value is equal to or greater than the first value, determines that the dialysis patient's body is overhydrated when the average value is equal to or less than the second value and the index of variation is equal to or less than the third value, and determines that the dialysis patient's body is neither overhydrated nor dehydrated when the average value exceeds the second value and is less than the first value, or when the average value is equal to or less than the second value and the index of variation exceeds the third value.

7. A computer program for evaluating the body fluid volume of a dialysis patient at the end of dialysis, comprising: a pulse pressure acquisition unit that acquires a first pulse pressure, which is the pulse pressure of the dialysis patient at the end of dialysis before the blood in the dialyzer and blood circuit is returned to the body of the dialysis patient, and a second pulse pressure, which is the pulse pressure of the dialysis patient at the end of blood return, the pulse pressure acquisition unit acquiring the first pulse pressure and the second pulse pressure in multiple consecutive dialysis sessions of the dialysis patient; a first calculation unit that calculates the rate of increase in pulse pressure from the first pulse pressure and the second pulse pressure, the first calculation unit calculating the rate of increase in pulse pressure for each of the multiple dialysis sessions from the first pulse pressure and the second pulse pressure of each of the multiple dialysis sessions; a second calculation unit that calculates at least one of an index indicating the average value and a index indicating the variation of the rate of increase in pulse pressure in the multiple dialysis sessions calculated by the first calculation unit; and an evaluation unit that evaluates the body fluid volume of the dialysis patient based on at least one of the indexes indicating the average value and the variation calculated by the second calculation unit.

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