Extracorporeal Blood Treatment Device And Method For Monitoring The Integrity Of A Dialyzer Of An Extracorporeal Blood Treatment Device

Abstract

The invention relates to an extracorporeal blood treatment device for carrying out an extracorporeal blood treatment, in which blood flows in an extracorporeal blood circuit A through the blood chamber 2 of a dialyser 1 which is divided by a semi-permeable membrane 4 into the blood chamber 2 and a dialysate chamber 3. The invention further relates a method for monitoring the integrity of a dialyser 1. The blood treatment device provides a preparation mode in preparation for the blood treatment, in which the dialysate chamber 3 of the dialyser 1 (filter) is filled with a liquid, while the blood chamber 2 is not filled with blood, and a treatment mode following the preparation mode, in which blood is conveyed through the blood chamber 2. For monitoring the integrity of the dialyser 1, in the preparation mode the fluid system B including the dialysate chamber 3, or a portion of the fluid system including the dialysate chamber, is filled with a liquid. At this time, however, the blood chamber 2 is not filled with blood. After the membrane of the dialyser 1 has been wetted with liquid, liquid is removed from the fluid system B including the dialysate chamber 3 such that a low pressure p is established in the fluid system. The control and arithmetic unit 29 of the blood treatment device is so configured that the increase in the amount of the low pressure p, measured by means of a pressure measuring apparatus 34, in a given time interval is determined, and the leakage rate LR of the fluid system is determined from the increase in the amount of the low pressure in a given time interval and the compliance C of the fluid system B including the dialysate chamber 3. A lack of integrity of the dialyser is then concluded on the basis of the determined leakage rate LR.

Claims

1. Extracorporeal blood treatment device for carrying out an extracorporeal blood treatment, in which blood flows in an extracorporeal blood circuit through the blood chamber of a dialyser which is separated by a semi-permeable membrane into the blood chamber and a dialysate chamber, the blood treatment device comprising: a fluid system including the dialysate chamber at least during operation, a pump system for filling the fluid system including the dialysate chamber with a liquid and for establishing a pressure difference between the blood chamber and the dialysate chamber, the pump system having at least one pump, a pressure measuring apparatus for measuring the pressure in the fluid system including the dialysate chamber for carrying out an integrity test for monitoring the integrity of the dialyser, a control and arithmetic unit which cooperates with the pump system and the pressure measuring apparatus and which provides a preparation mode in preparation for the blood treatment, wherein, for carrying out the preparation mode, the control and arithmetic unit is so configured that the fluid system including the dialysate chamber is filled with a liquid, the integrity test for monitoring the integrity of the dialyser is carried out after the fluid system including the dialysate chamber has been filled with a liquid, and the blood chamber is filled with a liquid after the integrity test has been carried out, the control and arithmetic unit being so configured for carrying out the integrity test in the preparation mode that a pressure difference is established between the blood chamber and the dialysate chamber in such a manner that the pressure in the blood chamber is greater than the pressure in the dialysate chamber, the increase in the pressure p, measured by the pressure measuring apparatus, in a given time interval being determined, and a leakage rate LR being determined from the increase in the pressure in a given time interval and the compliance C of the fluid system including the dialysate chamber, and a lack of integrity of the dialyser being concluded on the basis of the determined leakage rate LR.

2. Extracorporeal blood treatment device according to claim 1, wherein the control and arithmetic unit is so configured that, for establishing the pressure difference between the blood chamber and the dialysate chamber, liquid is removed by means of the pump system from the fluid system including the dialysate chamber or the pressure in the blood chamber is increased by means of the pump system by supplying air or liquid to the extracorporeal blood circuit.

3. Extracorporeal blood treatment device according to claim 1, wherein the control and arithmetic unit is so configured that the leakage rate LR is calculated according to the following equation:
LR=C dp/dt where C is the compliance C of the fluid system including the dialysate chamber, and dp/dt is the rate of pressure increase.

4. Extracorporeal blood treatment device according to claim 1, wherein the control and arithmetic unit is so configured that, for monitoring the integrity of the dialyser, in the preparation mode the compliance C is calculated from a volume of the liquid which is removed from the fluid system including the dialysate chamber and the fall in the pressure measured by means of the pressure measuring apparatus.

5. Extracorporeal blood treatment device according to claim 4, characterised in that the control and arithmetic unit is so configured that the compliance C is calculated according to the following equation:
C=dV/dp where dV is the volume of liquid removed from the fluid system including the dialysate chamber, and dp is the fall in pressure before removal and after removal of the liquid.

6. Extracorporeal blood treatment device according to claim 1, wherein the control and arithmetic unit is so configured that the determined leakage rate LR is compared with a given limit value for the leakage rate and a lack of integrity is concluded if the leakage rate does not fall below the given limit value in a given time interval.

7. Extracorporeal blood treatment device according to claim 2, wherein the pump system has an ultrafiltrate pump, and in that the control and arithmetic unit is so configured that the ultrafiltrate pump is operated to remove liquid from the fluid system including the dialysate chamber, such that a fall in pressure occurs in the fluid system including the dialysate chamber.

8. Extracorporeal blood treatment device according to claim 1, wherein the control and arithmetic unit is so configured that in the preparation mode, after the fluid system including the dialysate chamber has been filled with a liquid, the fluid system is flushed.

9. Method for monitoring the integrity of a dialyser of an extracorporeal blood treatment device for carrying out an extracorporeal blood treatment, in which blood flows in an extracorporeal blood circuit through the blood chamber of a dialyser which is separated by a semi-permeable membrane into the blood chamber and a dialysate chamber, wherein the blood treatment device provides a preparation mode in preparation for the blood treatment, in which the fluid system including the dialysate chamber is filled with a liquid, an integrity test for monitoring the integrity of the dialyser is carried out after the fluid system including the dialysate chamber has been filled, and the blood chamber is filled with a liquid after the integrity test has been carried out, wherein the following method steps are carried out for the integrity test in the preparation mode: establishing a pressure difference between the blood chamber and the dialysate chamber, such that the pressure in the blood chamber is greater than the pressure in the dialysate chamber, determining the increase in the pressure p in the fluid system including the dialysate chamber in a given time interval, and determining a leakage rate LR from the increase in the pressure in a given time interval and the compliance C of the fluid system including the dialysate chamber, and generating a control signal signalling the lack of integrity of the dialyser on the basis of the determined leakage rate.

10. Method for monitoring the integrity of a dialyser according to claim 9, wherein, for establishing a pressure difference between the blood chamber and the dialysate chamber, liquid is removed from the fluid system including the dialysate chamber or the pressure in the blood chamber is increased by means of the pump system by supplying air or liquid to the extracorporeal blood circuit.

11. Method for monitoring the integrity of a dialyser according to claim 9, wherein the leakage rate LR is determined according to the following equation:
LR=C dp/dt where C is the compliance C of the fluid system including the dialysate chamber, and dp/dt is the rate of pressure increase.

12. Method for monitoring the integrity of a dialyser according to claim 9, wherein, for monitoring the integrity of the dialyser, in the preparation mode the compliance C is calculated from a volume of the liquid which is removed from the fluid system including the dialysate chamber, and the fall in the measured pressure p.

13. Method for monitoring the integrity of a dialyser according to claim 12, wherein the compliance C of the fluid system is calculated according to the following equation:
C=dV/dp where dV is the volume of liquid removed from the fluid system including the dialysate chamber, and dp is the fall in pressure before removal and after removal of the liquid.

14. Method for monitoring the integrity of a dialyser according to claim 9, wherein the determined leakage rate LR is compared with a given limit value for the leakage rate, and a control signal signalling the lack of integrity of the dialyser is generated if the leakage rate does not fall below the given limit value in a given time interval.

15. Method for monitoring the integrity of a dialyser according to claim 9, wherein, after the fluid system including the dialysate chamber has been filled with a liquid, the fluid system is flushed using the liquid.

Description

[0036] The invention is described in detail below with reference to the figures, in which:

[0037] FIG. 1 is a simplified schematic view of an embodiment of a blood treatment device according to the invention,

[0038] FIG. 2 shows the pressure in the fluid system as a function of time for different dialysers, and

[0039] FIG. 3 shows the pressure in the fluid system as a function of time for the integrity test according to the invention in which the dialyser is filled with a liquid only on the dialysate side and for an integrity test in which the blood side of the dialyser was also filled with a liquid.

[0040] FIG. 1 is a highly simplified schematic view of the components of a blood treatment device according to the invention. The blood treatment device comprises an extracorporeal blood circuit A and a fluid system B. The extracorporeal blood circuit A includes the blood chamber 2, and the fluid system B includes the dialysate chamber 3 of a dialyser 1. The blood chamber 2 and the dialysate chamber 3 of the dialyser 1 are separated by a semi-permeable membrane 4. A blood supply line 5, in which a blood pump 6 is provided, leads from an arterial patient port 7 to the inlet of the blood chamber 2. Upstream of the blood pump 6, an arterial valve 8 can be situated in the blood supply line 5. From the outlet of the blood chamber 2, a blood discharge line 9, in which a liquid chamber (drip chamber) 10 can be connected, leads to a venous patient port 11. Downstream of the liquid chamber 10, a venous valve 12 is situated in the blood discharge line 9.

[0041] The extracorporeal blood circuit A and the fluid system B, or portions of the extracorporeal blood circuit or of the fluid system B, can be in the form of disposables intended for single use. In the following, the blood treatment device is described in the ready state, in which the disposable or disposables have been inserted into or fastened to the blood treatment device.

[0042] The fluid system B can further have a dialysate source 13 for providing fresh dialysate, which is connected via a first portion 14A of a dialysate supply line 14 to the inlet of a chamber 15A of a balancing unit 15. The second portion 14B of the dialysate supply line connects the outlet of one chamber 15A of the balancing unit 15 to the inlet of the dialysate chamber 3. The dialysate can be used as flushing or preparation liquid.

[0043] The outlet of the dialysate chamber 3 is connected via a first portion 16A of a dialysate discharge line 16 to the inlet of the other chamber 15B of the balancing unit 15. A dialysate pump 17 is situated in the first portion 16A of the dialysate discharge line 16. The outlet of the other chamber 15B of the balancing unit 15 is connected via the second portion 16B of the dialysate discharge line 16 to a drain 18. The balancing unit 15 can have further chambers.

[0044] A valve 19 is situated in the dialysate supply line 14 upstream of the dialysate chamber 3, and a valve 20 is situated in the dialysate discharge line 16 downstream of the dialysate chamber 3. The valves 19, 20 can be electromagnetically operable valves. From the first portion 16A of the dialysate discharge line 16, an ultrafiltrate line 23, in which an ultrafiltrate pump 24 is provided, leads to the second portion 16B of the dialysate discharge line 16. From a portion of the ultrafiltrate line 23 upstream of the ultrafiltrate pump 24, a bypass line 25, in which a bypass valve 26 is provided, can lead to a portion of the ultrafiltrate line 23 downstream of the ultrafiltrate pump 24. The blood pump 6, the dialysate pump 17 and the ultrafiltrate pump 24 can be occluding pumps. When the pumps are occluding pumps, valves for creating a closed volume can be omitted.

[0045] In the present embodiment, the blood supply and discharge lines 5, 9 of the extracorporeal blood circuit A are part of an exchangeable blood hose set, and the dialysate supply and discharge lines 14, 16 of the dialysate system B are fixed parts of the hydraulic system of the blood treatment device. The blood hose set and the dialyser 1 are intended for single use and are inserted in receivers (not shown). Instead of a hose set, it is also possible to provide an exchangeable cassette in which channels for the liquid, in particular the supply and discharge of blood, are formed. The receiver for the dialyser can be a holder.

[0046] The blood treatment device has a central control and arithmetic unit 29 for controlling all the components of the device. The central control and arithmetic unit 29 can have, for example, a general processor, a digital signal processor (DSP) for continuously processing digital signals, a microprocessor, an application-specific integrated circuit (ASIC), an integrated circuit consisting of logic elements (FPGA), or other integrated circuits (IC) or hardware components, in order to perform the individual method steps for controlling the blood treatment device. A data processing program (software) can run on the hardware components for performing the method steps. A plurality or a combination of the various components is also possible.

[0047] The control and arithmetic unit 29 is connected via control or data lines (not shown) to the pumps 6, 17, 24, the valves 8, 12, 19, 20 and the bypass valve 26, such that the flow rates of the pumps can be adjusted and the valves and the bypass valve can be actuated. The pumps 6, 17, 24, valves 8, 12, 19, 20 and the bypass valve 26 are part of a pump system 38 of the blood treatment device.

[0048] The control and arithmetic unit 29 has a memory 29A in which measured values and parameters can be stored. Furthermore, a display unit 30 and an alarm unit 31 are provided, which are connected via data lines 32, 33 to the control and arithmetic unit 29. The display unit 30 can have display elements, for example signal lamps, or a display for displaying various symbols, which indicate that the dialyser is in order or that the dialyser lacks integrity. The alarm unit 31 can have a signal generator for an acoustic and/or optical and/or tactile alarm.

[0049] The pressure in the fluid system B is measured by means of a pressure measuring apparatus 34. The pressure measuring apparatus 34 can have a first pressure sensor 34A which measures the pressure in the second portion 14B of the dialysate supply line 14, and/or have a second pressure sensor 34B which measures the pressure in the first portion 16A of the dialysate discharge line 16. The control and arithmetic unit 29 receives the signals from the pressure measuring apparatus 32 via data lines 35, 36. The measured pressure values are stored in the memory 29A of the control and arithmetic unit 29 for the calculation of various values.

[0050] The known blood treatment devices provide a treatment mode and a preparation mode preceding the treatment, in preparation for the treatment. During the actual blood treatment, the extracorporeal blood circuit A, which comprises the blood supply line 5, the blood chamber 2 of the dialyser 1 and the blood return line 9, is filled with blood, which is conveyed by the blood pump 6. In the preparation mode preceding the blood treatment, the blood chamber is not filled with blood.

[0051] The control and arithmetic unit 29 is so configured that the preparation mode or the treatment mode can be specified. Monitoring of the integrity of the membrane 3 of the dialyser 1 takes place in the preparation mode during a filling and flushing process, which is carried out in any case in preparation for the blood treatment. For the integrity test, the control and arithmetic unit 29 controls the individual components of the blood treatment device as follows, in order to carry out the following method steps.

[0052] The control and arithmetic unit 29 opens the valve 19 of the pump system 38 in the dialysate supply line 14 upstream of the dialysate chamber 3 and can close the valve 20 in the dialysate discharge line 16 downstream of the dialysate chamber 3. Dialysate is then conveyed from the dialysate source via the balancing unit 15 to the dialysate chamber 3. The filling pressure of the dialysate chamber 3 is measured by the pressure sensor 34A for measuring the pressure in the dialysate supply line 14 and monitored by the control and arithmetic unit 29. The air in the dialysate chamber 3 is thus able to escape via the membrane 4 of the dialyser into the blood chamber 2 and from the blood chamber via the open hose system of the extracorporeal blood circuit A. As soon as all the pores of the membrane 4 are wetted, the pressure in the dialysate supply line 14 increases sharply. When the filling pressure exceeds a given limit value, which is stored in the memory 29A, the control and arithmetic unit 29 opens the valve 20 in the dialysate discharge line 16, such that the dialysate chamber 3 is vigorously flushed, the dialysate flowing into the drain 18. The pressure in the dialysate supply line 14 then falls below the limit value again.

[0053] Alternatively, the valve 20 can also be opened, and further regions, depending on the position of the valves that are present, are filled.

[0054] The fluid system B including the dialysate chamber 3 can now be further flushed with dialysate with the valve 20 open, and therefore the hydraulic system is further ventilated. At the end of the flushing operation, the valve 19 in the dialysate supply line 14 is closed again. The membrane 4 of the dialyser 1 is now wetted with dialysate on the hydraulic side, and therefore the membrane is air-tight. On the blood side, however, the membrane has not been wetted with liquid, since the blood chamber has not yet been filled with blood. In the case of a hollow chamber filter, the lumen of the fibres of the membrane are still empty. As a result, the integrity test can be carried out in a relatively short time.

[0055] After the flushing operation, liquid, which in the present embodiment is dialysate as flushing liquid, is removed from at least a portion of the fluid system B including the dialysate chamber 3. In order to remove liquid, the control and arithmetic unit 29 operates the ultrafiltrate pump 24, the valve 19 in the dialysate supply line 14 being closed. The valve 26 in the bypass line 25 is likewise closed.

[0056] It should be noted at this point that, according to the invention, the fluid system B, during operation, only has to include the dialysate chamber and a pressure measuring apparatus. Further components shown may or may not be present, or may or may not belong to the fluid system B. Ultimately, any region of the hydraulic system can belong to the fluid system B according to the invention provided that there is a region which can be filled with liquid and from which liquid can be removed and in which the pressure can be measured and which also includes the dialysate chamber. In addition, this region should also be suitable for being shut off in a pressure-tight manner such that the pressure changes required for the pressure test described herein can be determined.

[0057] The use of an ultrafiltrate pump for removing the liquid has the advantage that a specific volume of liquid can be removed very accurately by means of this pump. This is a requirement for the correct use of an ultrafiltrate pump during the blood treatment. There are therefore used as ultrafiltrate pumps in blood treatment devices only pump types which, as a result of their construction, are able to remove from the system volumes which can be defined exactly. The ultrafiltrate pump can be a membrane pump. Alternatively, however, different pumps can be used. For example, a dialysate pump having a flow meter, for example having a Coriolis flow meter, can be used for pumping away the liquid.

[0058] In the present embodiment, in the dialysate discharge line 16 the pressure p.sub.t1 is measured before one or each pump stroke and the pressure p.sub.t2 is measured after one or each pump stroke. For at least one or each pump stroke, the control and arithmetic unit 29 calculates the compliance C of the portion of the fluid system B including the dialyser 1 from the known volume dV of a pump stroke and from the measured pressure p.sub.t1, p.sub.t2 before and after the relevant pump stroke. The compliance values, which are stored in the memory 29A, are calculated according to the following equation:

C=dV/(p.sub.t2p.sub.t1)

[0059] For the integrity test, it is necessary to generate a pressure difference across the membrane. In one embodiment, when the liquid is removed by means of the ultrafiltrate pump 24, a low pressure is established in the fluid system B that includes the dialysate chamber 3, since the wetted membrane 4 of the dialyser 1 is largely air-tight even if the membrane has defects, because the volume of air which could pass into the fluid system via the defects is low in relation to the volume of liquid that is removed.

[0060] The pressure is measured by means of the pressure sensor 34B in the dialysate discharge line 16. The ultrafiltrate pump 24 is operated until a given test pressure has been established. For this purpose, the current measured pressure can continuously be compared with the given test pressure. Since the compliance is determined at least for the last pump stroke, the compliance at the test pressure is also known. In a preferred embodiment, the compliance value determined at the test pressure is used as the basis for the further analysis. It is not necessary in this case to determine the compliance values for each pump stroke. However, it is also possible to use an average value for the compliance or a maximum or minimum compliance value as the basis for the further analysis.

[0061] If the test pressure has not been established even after a given maximum delivery volume of the ultrafiltrate pump 24, it is already concluded in advance that the membrane 4 of the dialyser 1 is not tight. It can also be concluded that there is a leak if the test pressure has not been established after a given time interval in which the ultrafiltrate pump has been running. If that is the case, the control and arithmetic unit 29 generates a control signal which signals the lack of integrity of the dialyser 1 and which is received by the display unit 30 and/or the alarm unit 31. The fact that the dialyser lacks integrity can then be displayed on the display unit 30 and/or an alarm can be given by the alarm unit 31. The defective dialyser must then be replaced by a new dialyser.

[0062] The actual integrity test then takes place, by means of which the integrity of the dialyser can reliably be checked in a relatively short test time, it being possible for even slight leaks to be detected.

[0063] The low pressure increases during operation of the ultrafiltrate pump 24, in other words the pressure difference relative to the blood chamber becomes increasingly greater. If the test low pressure for the integrity test is reached, the integrity test can begin. For this purpose, the change in the pressure over time in the closed fluid system B is measured and the rate of pressure increase p/t.sub.At.sub.B=p.sub.tAp.sub.tB /t.sub.At.sub.B is determined, where p.sub.tA is the pressure measured at time t.sub.A, and p.sub.tB is the pressure measured at the later time t.sub.B, and t.sub.At.sub.B is the time interval between the start of the measurement at t.sub.A and the later time t.sub.B.

[0064] From the rate of pressure increase and the compliance C determined, for example, for the last pump stroke, that is to say the compliance at the test pressure, the control and arithmetic unit 29 calculates the leakage rate LR according to the following equation:

LR=C p/t.sub.At.sub.B

[0065] Since this determination of LR can take place continuously or at one or more predetermined times, an averaged leakage rate for the time interval t.sub.A to t.sub.B is calculated.

[0066] The calculated leakage rate LR is compared with a given limit value for the leakage rate LR, which is assumed for an intact dialyser. If the calculated leakage rate LR is smaller than the given limit value, it is concluded that the dialyser is intact. The control and arithmetic unit 29 can then send a control signal signalling the integrity of the dialyser to the display unit 30, which is displayed on the display unit. The control and arithmetic unit 29 can also generate a control signal which carries out an intervention in the machine control system. For example, specification of the treatment mode can be prevented following detection of a membrane that is not tight, or the treatment mode can be enabled only if sufficient integrity of the dialyser is detected.

[0067] For the integrity test, a maximum test time is specified, in which liquid is removed from the fluid system in order to establish the low pressure. If the calculated leakage rate LR is not smaller than the given limit value during the maximum test time, it is concluded that the membrane 4 is not tight. In this case, the control and arithmetic unit 29 generates a control signal signalling the lack of integrity of the dialyser 1, which is received by the display unit 30 and/or the alarm unit 31, such that it is then indicated on the display unit that the membrane of the dialyser is not tight, and an alarm is given by the alarm unit. The control and arithmetic unit 29 can also generate a control signal which carries out an intervention in the machine control system such that the blood treatment mode is not enabled, such that it is not possible to carry out a treatment using a defective dialyser.

[0068] In the present embodiment, the ultrafiltrate pump 24 is operated cyclically. It is also possible to calculate the compliance C and the leakage rate LR, taking the compliance C into consideration, for each cycle (pump stroke) or to determine the compliance and the leakage rate for any given time interval, which can include a plurality of pump strokes.

[0069] In the case of a leakage rate which is greater than zero, the test pressure in the fluid system can readily fall. However, the measurement result can be distorted thereby only slightly. In order to avoid this measurement error, the control and arithmetic unit 29 can be so configured that the ultrafiltrate pump 24 is so controlled that the given test pressure established in the portion of the fluid system including the dialysate chamber 3 is kept constant. For this purpose, a delivery rate for the ultrafiltrate pump 24 is set. Since the test pressure falls according to the leakage rate, the delivery rate of the ultrafiltration pump 24 must directly correspond to the leakage rate in order to keep the test pressure constant. In this embodiment, the control device has a pressure-based feedback control for keeping the test pressure constant. In this embodiment, the blood treatment device, or the method, thus has to be configured to determine the leakage rate without explicitly determining the compliance and to thus carry out the integrity test according to the above description. The compliance is taken into consideration inherently in the feedback control, in that the dynamics of the pressure response of the system already depends on the compliance.

[0070] In a further embodiment, the pressure difference is generated by building up pressure in the blood chamber. For this purpose, the pressure in the blood chamber can be increased by supplying air or liquid to the extracorporeal blood circuit (A), without filling the blood chamber with liquid. Otherwise, the above observations relating to the establishment of the pressure difference by decreasing the pressure in the dialysate chamber apply analogously.

[0071] FIG. 2 shows the change over time in the low pressure p measured by means of the pressure sensor 34B in the blood discharge line 16, while the ultrafiltrate pump 24 removes liquid from the fluid system. The low pressure for three different dialyser types is shown in FIG. 2. It is shown that the low pressure increases while liquid is being removed from the fluid system. With each pump stroke, the low pressure increases stepwise by a specific amount until the test pressure is reached. Furthermore, it can be seen that there is a slight rise after the last ultrafiltration pump stroke. The leakage rate LR is then determined from this rise.

[0072] FIG. 3 shows the change over time in the leakage rate LR in the case of a measurement using a dialyser of which the dialysate chamber is filled with liquid, the blood chamber having been filled with liquid once (graph II), in comparison with a dialyser of which the dialysate chamber is filled with liquid, the blood chamber not having been filled with liquid (graph I). It is shown that a minimum leakage rate LR is reached after only about 20 seconds in the case of a dialyser of which the blood chamber was not filled with liquid, while the minimum leakage rate LR is reached only after about 200 seconds in the case of a dialyser of which the blood chamber was filled with liquid. Consequently, the measuring time for checking the integrity of the dialyser membrane can be shortened significantly using the method according to the invention as compared with a conventional method.

[0073] After the integrity test, the extracorporeal blood circuit A is filled with a preparation liquid. Only after filling with the preparation liquid, for example dialysate, is the membrane of the dialyser wetted with liquid also on the blood side. For filling the blood chamber with a pre-liquid in the preparation mode, liquid from the hydraulic system B or liquid from a container can be supplied to the extracorporeal blood circuit A. For flushing the extracorporeal circuit A, the flushing liquid can, via a connection, be supplied to the fluid system A or guided into a separate container.