AUTOMATIC REINFUSION OF BLOOD FOLLOWING A BLOOD TREATMENT THERAPY

Abstract

An extracorporeal blood treatment device includes an extracorporeal circuit, a dialyzer, a dialyzing liquid circuit and a control unit. A venous section and an arterial section of the extracorporeal circuit each includes a sensor configured to acquire a hematocrit percentage in a liquid flowing through the corresponding section. The control unit controls reinfusion of blood such that a dialyzing liquid is supplied from the dialyzing liquid circuit via a dialyzer membrane to the extracorporeal circuit, which displaces blood present in the extracorporeal circuit towards a patient to return the blood to the patient via the venous section and arterial section. Reinfusion in the corresponding section of the extracorporeal circuit is discontinued if it is acquired by the corresponding sensor or calculated or predicted by the control unit based on information acquired by the corresponding sensor that the hematocrit percentage falls below a predetermined limit value.

Claims

1. An extracorporeal blood treatment device comprising: an extracorporeal circuit comprising an arterial section and a venous section; a dialyzer; and a dialyzing liquid circuit, the extracorporeal circuit and the dialyzing liquid circuit being separated from each other by a membrane provided in the dialyzer; a first sensor being provided in the venous section, the first sensor being configured to acquire a hematocrit percentage in liquid flowing through the venous section, a second sensor being provided in the arterial section, the second sensor being configured to acquire a hematocrit percentage in liquid flowing through the arterial section, and the extracorporeal blood treatment device further comprising a control unit configured to control a reinfusion of blood such that a dialyzing liquid is supplied from the dialyzing liquid circuit via the membrane to the extracorporeal circuit, which, during the reinfusion of blood, displaces blood present in the extracorporeal circuit towards a patient to return blood to the patient via both the venous section and the arterial section, the control unit being configured to discontinue the reinfusion of blood via the venous section when the hematocrit percentage acquired by the first sensor or calculated or predicted by the control unit based on information acquired by the first sensor falls below a predetermined limit value, the control unit further being configured to discontinue the reinfusion of blood via the arterial section when the hematocrit percentage acquired by the second sensor or calculated or predicted by the control unit based on information acquired by the second sensor falls below the predetermined limit value.

2. The extracorporeal blood treatment device according to claim 1, wherein the predetermined limit value is less than or equal to 10%.

3. The extracorporeal blood treatment device according to claim 1, further comprising an arterial blood pump in the arterial section, the arterial blood pump being configured for a change of direction of rotation, and the control unit controlling the arterial blood pump during the reinfusion of blood via the arterial section so that the arterial blood pump rotates against a therapy direction.

4. The extracorporeal blood treatment device according to claim 1, wherein the control unit is configured to perform the reinfusion of blood via the venous section and the reinfusion of blood via the arterial section in parallel.

5. The extracorporeal blood treatment device according to claim 1, wherein the control unit is configured to serially perform the reinfusion of blood via the venous section and the reinfusion of blood via the arterial section.

6. The extracorporeal blood treatment device according to claim 1, wherein the control unit is configured to control the reinfusion of blood as a function of the dialyzer used.

7. The extracorporeal blood treatment device according to claim 1, wherein the control unit is configured to perform, after a blood treatment therapy and before the reinfusion of blood, a safety air removal step, by which air or, respectively, an air bubble is removed from the arterial section.

8. The extracorporeal blood treatment device according to claim 7, further comprising an arterial tube clamp and an arterial blood pump provided in the arterial section, and a venous expansion chamber provided in the venous section, wherein the control unit performs the safety air removal step such that initially the arterial section is clamped off for a predetermined period of time via the arterial tube clamp, while the arterial blood pump continues to run in a therapy direction, wherein a resulting negative pressure carries away the air or, respectively, air bubble present in the arterial section and conveys the air or, respectively, air bubble into the venous section, where the air or, respectively, air bubble is eliminated in the venous expansion chamber.

9. The extracorporeal blood treatment device according to claim 1, wherein the first sensor is a venous safety air detector with integrated red detector, which is configured to detect air or air bubbles in the liquid flowing through the venous section and to acquire the hematocrit percentage of the liquid as termination criterion of the reinfusion of blood via the venous section, and wherein the second sensor is an arterial safety air detector with integrated red detector, which is configured to detect air or air bubbles in the liquid flowing through the arterial section and to acquire the hematocrit percentage of the liquid as termination criterion of the reinfusion of blood via the arterial section.

10. The extracorporeal blood treatment device according to claim 7, wherein the first sensor is a venous safety air detector with integrated red detector, which is configured to detect air or air bubbles in the liquid flowing through the venous section and to acquire the hematocrit percentage of the liquid as termination criterion of the reinfusion via the venous section, and in that the second sensor is a hematocrit sensor which is configured to acquire information about the hematocrit percentage in the liquid during the reinfusion of blood and to forward said information to the control unit .

11. The extracorporeal blood treatment device according to claim 10, wherein the control unit is configured to make, based on the information about the hematocrit percentage in the liquid, a calculation or a prediction as to when the hematocrit percentage of the liquid falls below the predetermined limit value.

12. The extracorporeal blood treatment device according to claim 11, wherein the control unit is configured to make the calculation or the prediction by a linear function when performing the reinfusion of blood via the venous section and the reinfusion of blood via the arterial section serially or when a reinfusion flow in the arterial section or the venous section is large or, respectively, is greater than a predetermined threshold value.

13. The extracorporeal blood treatment device according to claim 11, wherein the control unit is configured to make the calculation or the prediction by a Gaussian function when performing the reinfusion of blood via the venous section and the reinfusion of blood via the arterial section in parallel or when a reinfusion flow in the arterial section or the venous section is small or, respectively, is smaller than a predetermined threshold value.

14. A method for automatically performing a reinfusion of blood after a blood treatment therapy, the method comprising the steps of: supplying a dialyzing liquid from a dialyzing liquid circuit via a membrane of a dialyzer to an extracorporeal circuit; displacing blood present in the extracorporeal circuit towards a patient; returning the blood to the patient via both a venous section of the extracorporeal circuit and an arterial section of the extracorporeal circuit; discontinuing the reinfusion of blood via the venous section when it is acquired by a first sensor provided in the venous section or if, based on information acquired by the first sensor, it is predicted or calculated that a hematocrit percentage of a liquid containing blood flowing through the venous section falls below a predetermined limit value; and discontinuing of the reinfusion of blood via the arterial section if it is acquired by a second sensor provided in the arterial section or if, based on information acquired by the second sensor, it is predicted or calculated that a hematocrit percentage of a liquid containing blood flowing through the arterial section falls below a predetermined limit value.

15. The extracorporeal blood treatment device according to claim 1, wherein the predetermined limit value for the hematocrit percentage is between 1% and 5%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The disclosure is further explained below with reference to figures.

[0060] FIG. 1 shows an extracorporeal blood treatment device according to a first preferred embodiment of the present disclosure, with reference to which the automatic reinfusion according to the disclosure is explained;

[0061] FIG. 2 shows an extracorporeal blood treatment device according to a second preferred embodiment of the present disclosure, with reference to which the automatic reinfusion according to the disclosure is explained;

[0062] FIG. 3 shows a view of an arterial blood pump before a safety air removal step according to the disclosure is performed;

[0063] FIG. 4 shows a view of the arterial blood pump after the safety air removal step according to the disclosure has been performed;

[0064] FIG. 5 shows a diagram showing the curve of a volume flow of air supplied to a patient during the reinfusion via the arterial section of the extracorporeal circuit over time after the safety air removal step according to the disclosure has been performed;

[0065] FIG. 6 shows a diagram which ought to illustrate a prediction of a hematocrit percentage by means of a linear function when the reinfusion via the arterial section and the venous section is performed serially;

[0066] FIG. 7 shows a diagram which ought to illustrate a prediction of a hematocrit percentage by means of a linear function when the reinfusion via the arterial section and the venous section is performed in parallel; and

[0067] FIG. 8 shows a diagram which ought to illustrate a prediction of a hematocrit percentage by means of a Gaussian function when the reinfusion via the arterial section and the venous section is performed in parallel.

DETAILED DESCRIPTION

[0068] The figures are of a schematic nature and are intended solely for the understanding of the disclosure. Identical elements are provided with the same reference signs. The features of the individual embodiments may be interchanged unless this is explicitly described otherwise.

[0069] FIG. 1 shows an extracorporeal blood treatment device (dialysis machine) 2 according to a first preferred embodiment of the present disclosure, with reference to which the automatic reinfusion according to the disclosure is explained.

[0070] The extracorporeal blood treatment device 2 principally comprises an extracorporeal circuit (A/V tubing system) 4, a dialyzer 6, and a dialyzing liquid circuit 8. Thereby, the extracorporeal circuit 4 and the dialyzing liquid circuit 8 are separated from each other by a membrane 10 provided in the dialyzer 6.

[0071] The extracorporeal circuit 4 includes an arterial section 12, which is located upstream of the dialyzer 6, and a venous section 14, which is located downstream of the dialyzer 6.

[0072] As shown in FIG. 1, the arterial section 12 and the venous section 14 are coupled to a patient 15. In other words, an end of the arterial section 12 is coupled to an artery of the patient 15 and an end of the venous section 14 is coupled to a vein of the patient 15.

[0073] In the venous section 14 of the extracorporeal circuit 4, downstream of the dialyzer 6 (that is, starting from the dialyzer 6 in a direction towards the end of the venous section 14), a venous expansion chamber or, respectively, air trap 16, a venous safety air detector with (an) integrated red detector 18, and a venous tube clamp 20 are provided.

[0074] In the arterial section 12, starting from the patient-side end of the arterial section 12 in a direction towards the dialyzer 6, an arterial tube clamp 22, an arterial safety air detector with (an) integrated red detector 24 and an (arterial) blood pump 26 are provided. As can be seen in FIG. 1, the extracorporeal circuit 4 (in particular a blood pump adapter thereof) is already inserted into the blood pump 26, which is preferably formed as a roller pump or, respectively, peristaltic pump and is configured to supply a fluid/ a liquid by squeezing (of) a tube.

[0075] In the arterial section 12, an arterial pressure upstream of or, respectively, before the blood pump 26 may be measured by an arterial pressure sensor 28. Furthermore, a dialyzer inlet pressure downstream of or, respectively, after the blood pump 26 and upstream of or, respectively, before the dialyzer 6 (between the dialyzer 6 and the blood pump 26) may be measured via a dialyzer inlet pressure sensor 30. In the venous section 14, a venous pressure at/ downstream of the venous expansion chamber or, respectively, air trap 16 may be measured via a venous pressure sensor 32. The pressure sensors 28, 30, 32 provided in the extracorporeal circuit 4 may measure/ acquire/ monitor the pressure at the respective locations in the extracorporeal circuit 4 at which these are arranged/ provided.

[0076] The dialyzer liquid circuit 8 includes a dialyzer inlet valve 34, a dialyzer outlet valve 36, a flow pump-inlet 38 and a flow pump-outlet 40. However, it is generally sufficient if only one flow pump, for example the flow pump-inlet 38, is provided in the dialyzer liquid circuit 8. The dialyzer inlet valve 34 and the flow pump-inlet 38 are thereby provided/ arranged at a dialyzing liquid inflow 42 upstream of the dialyzer 6. The dialyzer outlet valve 36 and the flow pump-outlet 40 are provided/ arranged at a dialyzing liquid outflow 44 downstream of the dialyzer 6. The flow pump-inlet 38 and the flow pump-outlet 40 are preferably gear pumps.

[0077] The extracorporeal blood treatment device 2 further has a control unit 46, which is preferably formed as a processor, in particular as a central computing/ or, respectively, processing unit (CPU). The control unit 46 receives information from sensors which are provided in the extracorporeal blood treatment device 2. Merely by way of example, the sensors shown in FIG. 1 ought to be mentioned, i.e. the arterial pressure sensor 28, the dialyzer inlet pressure sensor 30, the venous pressure sensor 32, the arterial safety air detector with integrated red detector 24, the venous safety air detector with integrated red detector 18, etc. On the other hand, the control unit 46 controls or, respectively, actuates actuators which are provided in the extracorporeal blood treatment device 2. Merely by way of example, the valves, pumps, tube clamps, etc. shown in FIGS. 1, i.e., in particular the dialyzer inlet valve 34, the dialyzer outlet valve 36, the flow pump-inlet 38, the flow pump-outlet 40, the (arterial) blood pump 26, the arterial tube clamp 22, the venous tube clamp 20, etc., ought to be thereby mentioned.

[0078] The structure of an extracorporeal blood treatment device (dialysis machine) 2 (second preferred embodiment of the present disclosure) shown in FIG. 2 differs from the structure shown in FIG. 1 in terms of hardware only in that no arterial safety air detector with integrated red detector 24 is provided, but instead a hematocrit sensor (HTC sensor) 48 is arranged in the arterial section 12 of the extracorporeal circuit 4. Otherwise, the structure shown in FIG. 2 is identical to the structure shown in FIG. 1, so that the preceding explanations or, respectively, descriptions apply mutatis mutandis to the structure shown in FIG. 2 and are therefore not repeated.

[0079] FIG. 1 and FIG. 2 each show a state immediately after completion of a blood treatment therapy. In this state, it is desirable to return/ to reinfuse the blood still present in the extracorporeal circuit 4 to the patient.

[0080] In the embodiment shown in FIG. 1, a safety air removal step may optionally be performed after completion of the blood treatment therapy and before the start of the reinfusion. In the embodiment shown in FIG. 2, this safety air removal step is mandatory. The reason for this is that in the embodiment shown in FIG. 2, there is no safety air detector in the arterial section 12.

[0081] The control unit 46 performs the safety air removal step such that it initially clamps off the arterial section 12 for approximately two seconds via the arterial tube clamp 22 while the arterial blood pump 26 continues to run in therapy direction. Thereby a negative pressure is created in the arterial section 12, which entrains any air or air bubble 50 that may be present and carries it into the venous section 14, where the air or air bubble 50 is eliminated in the venous expansion chamber 16.

[0082] As can be seen from FIG. 3, after completion of a blood treatment therapy, often an air bubble 50 is present at an inlet of the arterial blood pump 26. Such an air bubble 50 can be suitably removed by the safety air removal step according to the disclosure. In particular, FIG. 4 shows the arterial blood pump 26 after the said safety air removal step has been performed. An air bubble 50 is no longer present in FIG. 4 and has been suitably eliminated by the safety air removal step. This is further illustrated by the diagram shown in FIG. 5. In FIG. 5, the volume/ the flow rate/ flow of air bubbles/ microbubbles over time during the arterial reinfusion is shown after the safety air removal step has been performed. It is shown that the volume/ the flow of the air bubbles is maximum 19 nl/s. This flow rate of air bubbles is far below a regimented maximum flow rate (500 nl/(s*kg)), so that the safety air removal step according to the disclosure enables a reliable removal of the air.

[0083] In the present case, the control unit 46 is principally configured to automatically control a reinfusion of blood after the blood treatment therapy or, respectively, if applicable, after the safety air removal step, such that a dialyzing liquid is supplied from the dialyzing liquid circuit 8 via the membrane 10 of the dialyzer 6 to the extracorporeal circuit 4, which during the reinfusion displaces the blood present in the extracorporeal circuit 4 towards the patient 15 in order to return the blood to the patient 15 both via the venous section 14 and via the arterial section 12.

[0084] The control unit 46 thereto actuates, according to the present disclosure, components present in the dialyzing liquid circuit 8 to create an excess pressure in the dialyzing liquid circuit 8 which causes that dialyzing liquid/ reinfusion liquid passes across the membrane 10 of the dialyzer 6. Preferably, the positive pressure is thereby created by the control unit 46 actuating the flow pump-inlet 38 to pump dialyzing liquid into the dialyzer 6 while the dialyzer inlet valve 34 is opened, the dialyzer outlet valve 36 is closed, and the flow pump-outlet 40 is stopped. Thus, a suitable pressure (transmembrane pressure) is exerted on the membrane 10 of the dialyzer 6 by the dialyzing liquid. This pressure causes that dialyzing liquid passes over from the dialyzing liquid circuit 8 to the extracorporeal circuit 4 across the membrane 10 of the dialyzer 6 at a defined flow (flow rate/ volume flow), for example 100 ml/min (depending on the dialyzer used).

[0085] In principle, the control unit 46 may perform the control depending on the dialyzer 6 used. For this purpose, the control unit 46 classifies the dialyzer 6 used, for example, as high-flux dialyzer or as low-flux dialyzer and performs, on the basis of this classification, in particular by accordingly actuating (of) the flow pump-inlet 38, a high-flux control or a low-flux control.

[0086] According to the present disclosure, the control unit 46 may perform the reinfusion via the arterial section 12 and via the venous section 14 in parallel or serially.

[0087] During the parallel reinfusion, the arterial blood pump 26 is operated by the control unit 46 against the therapy direction to supply blood/ liquid from the dialyzer 6 towards the end of the arterial section 12. For this purpose, the blood pump 26 may be set by the control unit 46 to a constant supply rate that is lower than the flow across the membrane 10 of the dialyzer 6. For example, the supply rate of the blood pump 26 may be set to 50 ml/min. When the defined flow across the membrane 10 of the dialyzer 6 is 100 ml/min, the flow in the venous section 14 in the therapy direction towards the end of the venous section 14 corresponds to the arterial flow. Now, when both the arterial tube clamp 22 and the venous tube clamp 20 are opened, the blood in both the arterial section 12 and the venous section 14 of the extracorporeal circuit 4 can be displaced towards the patient 15 by the dialyzing liquid passing over. The parallel reinfusion is terminated if/when both the arterial reinfusion and the venous reinfusion have been discontinued by the control unit 46 (by closing the arterial tube clamp 22 and the venous tube clamp 20).

[0088] If, during the parallel reinfusion, a blood reinfusion via the venous section 14 is discontinued earlier than a blood reinfusion via the arterial section 12, the control unit 46 closes the venous tube clamp 20 and increases the supply rate of the arterial blood pump 26. With an earlier discontinuation of the reinfusion via the arterial section 12, the control unit 46 stops the arterial blood pump 26 and closes the arterial tube clamp 22, so that the dialyzing liquid passing over now displaces only the remaining blood in the venous section 14.

[0089] In the serial reinfusion, for example, initially the blood from the venous section 14 may be returned to the patient 15, and only then the blood from the arterial section 12 be reinfused. In this case, the arterial blood pump 26 is stopped, the venous tube clamp 20 is opened, and the blood in the venous section 14 is displaced towards the patient 15 by the dialyzing liquid passing over. After a discontinuation of the venous reinfusion (by closing of the venous tube clamp 20), the arterial tube clamp 22 is opened (or remains open) and the arterial blood pump 26 begins to rotate against the therapy direction, so that the blood from the arterial section 12 is now also returned to the patient 15. The supply rate of the arterial blood pump 26 may thereby be adjusted to the flow of the dialyzing liquid passing over through the membrane 10. By a discontinuation of the arterial reinfusion, the serial reinfusion method is altogether terminated.

[0090] Alternatively, during the serial reinfusion, initially blood from the arterial section 12 may be returned to the patient 15, and only then the blood from the venous section 14 be reinfused. In this case, initially the venous tube clamp 20 is closed or, respectively, remains closed, the arterial tube clamp 22 is opened or, respectively, remains opened, and the arterial blood pump 26 starts to rotate against the therapy direction so that the blood from the arterial section 12 is returned to the patient 15. The supply rate of the arterial blood pump 26 is thereby adjusted to the flow of dialyzing liquid passing over through the membrane 10. After a termination of the arterial reinfusion (for example, by stopping of the arterial blood pump 26/ closing of the arterial tube clamp 22), the venous tube clamp 20 is opened, and the blood in the venous section 14 is displaced towards the patient 15 by the dialyzing liquid passing over. By a discontinuation of the venous reinfusion, the serial reinfusion method is altogether terminated.

[0091] In the following, the first preferred embodiment of the present disclosure according to FIG. 1 will be discussed in more detail. According to this embodiment, a safety air detector with integrated red detector is provided in both the arterial section 12 and the venous section 14, namely the arterial safety air detector with integrated red detector 24 and the venous safety air detector with integrated red detector 18. These two safety air detectors with integrated red detectors 18, 24 reliably detect air or air bubbles. If air or, respectively, air bubbles are detected, the control unit according to this embodiment discontinues the reinfusion by stopping (of) the arterial blood pump 26 or by closing (of) the arterial tube clamp 22 or (of) the venous tube clamp 20.

[0092] The arterial safety air detectors with integrated red detectors 18, 24 are configured to still determine a hematocrit percentage quite accurately even at relatively small percentage values. According to the first preferred embodiment, the arterial reinfusion is discontinued if/when the arterial safety air detector with integrated red detector 24 acquires that the hematocrit percentage in an end region of the arterial section 12 is below the predetermined limit value, which is preferably 3%. The venous reinfusion is discontinued if/when the venous safety air detector with integrated red detector 18 acquires that the hematocrit percentage in an end region of the venous section 12 is below the predetermined limit value.

[0093] In the following, the second preferred embodiment of the present disclosure according to FIG. 2 will be discussed in further detail. According to this embodiment, the venous safety air detector with integrated red detector 18 is provided in the venous section 14 and the hematocrit sensor/ HTC sensor 48 is provided in the arterial section 12.

[0094] Since the hematocrit sensor 48 can reliably measure a hematocrit value/percentage only in a range between 20% and 55%, the predetermined limit value is according to the disclosure less than 10%, in particular 3%, the measurement results of the hematocrit sensor 48 are according to the disclosure intelligently evaluated by the control unit 46 to be able to predict/ calculate when the predetermined limit value is fallen short of.

[0095] Such an intelligent evaluation is illustrated for the serial reinfusion (blood return via both the arterial section 12 and the venous section 14 at a flow rate of 100 ml/min) with reference to the diagram shown in FIG. 6. For the parallel reinfusion (blood return via both the arterial section 12 and the venous section 14 at a flow rate of 50 ml/min), such an intelligent evaluation is illustrated with reference to the diagrams in FIG. 7 and FIG. 8.

[0096] In order to be able to evaluate the hematocrit sensor 48 intelligently, a measurement curve of the hematocrit sensor 48 must be compared with an actual curve of the hematocrit percentage. For experimental purposes, an SADRDV sensor as reference sensor was integrated into the arterial section 12 for this purpose. For the experiments described below, a high-flux dialyzer available under the registered trademark XEVONTA® HI 23 was used.

[0097] In FIG. 6, for the serial blood reinfusion, only the curve of the hematocrit percentage for the arterial blood reinfusion measured by the hematocrit sensor 48 is shown. In the experiment, the blood tubing system between the hematocrit sensor 48 and the dialyzer 6 held approximately 40 ml. At a flow of 100 ml/min, the result is that the blood passes the hematocrit sensor 48 relatively undiluted for about 24 seconds (only slight decrease in the hematocrit percentage in FIG. 6). After 24 seconds, the hematocrit percentage decreases strongly until it reaches within 17 seconds a value of 0% (according to hematocrit sensor 48). When the hematocrit sensor 48 acquires the strong decrease of the hematocrit percentage, a point P1 can be defined. A second point P2 can be defined when the hematocrit percentage measured by the hematocrit sensor 48 is at a percentage value at which the hematocrit sensor 48 still measures accurately, such as at 20%. In FIGS. 6, P2 was defined at a hematocrit percentage of 10%. Through the points P1 and P, a linear function f(t) = -1.8 * t + 72.6 (for t > 24 s) is defined. For f(t) = 0, this results in a time of 40 seconds. However, due to the reference measurement with the SADRDV sensor, it is known that the hematocrit percentage after 55 seconds only falls below the predetermined limit value of 3%, resulting in an offset (for the dialyzer used, the flow set, and the tubing system used) of 15 seconds. Against this background, the control unit 46 may define the points P1 and P2 for the intelligent evaluation of the measurement results of the hematocrit sensor, define a linear function f(t) which passes through the points P1 and P2, and if according to the linear function f(t) = 0, add, if applicable, an offset to determine when the predetermined limit value is fallen short of. However, this approximation only works if the offset is small (in particular smaller than 20 seconds).

[0098] According to FIG. 7, an attempt was made to determine, also in the case of the parallel reinfusion, when the predetermined limit value is fallen short of, by fitting of a linear function to the measurement curve of the hematocrit sensor 48. As can be seen from FIG. 7, the curve of the hematocrit percentage measured by the hematocrit sensor 48 in the parallel reinfusion differs from that in the serial reinfusion. In particular, the hematocrit percentage in FIG. 7 does not decrease significantly during the first 63 seconds because the blood in the arterial section 12 of the extracorporeal circuit 4 passes the hematocrit sensor 48 relatively undiluted. Since there is a flow of only 50 ml/min, this process takes about twice as long as with the serial reinfusion. Thereafter, the hematocrit percentage drops with a constant gradient to 20% within 34 seconds. This is followed by a rapid decline to a hematocrit percentage of 0% within 18 seconds. Overall, thus, a different decrease in/of the hematocrit percentage is observed in the value range from 33% to 17% and in the value range from 17% to 0%. Against this background, it may be assumed that the reliable measuring range of the hematocrit sensor 48 extends to only about 20%. In this range, a linear function was fitted in FIG. 7, with the following functional equation: f(t) = -0.36*t + 54.23 [t>48 seconds]. For this function it is valid, that it has f(t) = 0 at 156 seconds. However, the actual time measured with the reference sensor until the predetermined limit value of 3% is fallen short of presently is 221 seconds. Against this background, in case of the parallel reinfusion, the offset is too large to predict a falling short of the predetermined limit value with a linear function.

[0099] As shown in FIG. 8, it has according to the disclosure been found that a first-order Gaussian function may be used, in the parallel reinfusion, for the prediction/ calculation, when the hematocrit percentage falls short of/below the predetermined limit value. In particular, the Gaussian function can be derived when the hematocrit percentage is recorded from the hematocrit sensor 48 up to 20%. In particular, three points P0, P1, and P2 of the hematocrit curve are used for the derivation of the Gaussian function, whereby P0 is the starting point, P1 is the point from which the hematocrit percentage decreases with a constant gradient, and P2 is the point up to which the hematocrit sensor measures reliably (approximately at 20%). Now, if the maximum Pmax of the Gaussian function is positioned such that it is exactly in the middle between P0 and P1 on the time axis, and the inflection point Pinflection of the Gaussian function is defined such that it is exactly in the middle between P1 and P2, the Gaussian function can be defined as shown in FIG. 8 as follows:

[00001]$f\left(t\right)=37,3\ast \exp \left[-{\left(\frac{\tau -31,1}{57,1}\right)}^2\right]$

As can be seen from FIG. 8, it is valid for this function that it has f(t) = 0 at about 216 seconds. Thus, with this function it can be predicted in a suitable way, in particular if a small offset is added, when the predetermined limit value of 3% will be/is fallen short of.