EP4142823A1

EP4142823A1 - Extracorporeal blood treatment device

Info

Publication number: EP4142823A1
Application number: EP21721430.3A
Authority: EP
Inventors: Alfred Gagel; Burkard KELLER; Peter KLÖFFEL; Martin Thys
Original assignee: Fresenius Medical Care Deutschland GmbH
Current assignee: Fresenius Medical Care Deutschland GmbH
Priority date: 2020-04-30
Filing date: 2021-04-21
Publication date: 2023-03-08
Also published as: DE102020111764A1; CA3175697A1; AU2021262429A1; CN115461099A; US20230158217A1; WO2021219451A1; JP2023523467A

Abstract

The invention relates to an extracorporeal blood treatment device which has a blood treatment unit 1 which is divided by a semipermeable membrane 2 into a first compartment 3, which is part of a liquid system II, and a second compartment 4, which is part of an extracorporeal blood circuit I. Furthermore, the invention relates to a method for operating a blood treatment device of this kind. The blood treatment device according to the invention has a pressure-based control device 32 which cooperates with the control unit for a valve device 21 and is designed in such a way that a liquid connection between an upstream portion 20A and a downstream portion 20B of a flow path 20 can be established for a particular operating mode only if the pressure-based control device 32 detects an operating state in which it is ensured that, for a particular operating mode, liquid flows in the flow path 20 in the direction of a flow path 10 leading to an outlet 11. It is thus ensured that the liquid in question can flow only into the flow path 10 that leads to the outlet 11, but cannot pass into another flow path 8 in which fresh treatment liquid is located.

Description

EXTRACORPORAL BLOOD TREATMENT DEVICE

The invention relates to an extracorporeal blood treatment device which has a blood treatment unit which is divided by a semipermeable membrane into a first compartment, which is part of a fluid system, and a second compartment, which is part of an extracorporeal blood circuit. The invention also relates to a method for operating such a blood treatment device.

The known dialysis devices have an extracorporeal blood circuit and a dialysis fluid system. The dialysis fluid system comprises a dialysis fluid supply line which leads from a dialysis fluid source to the dialysis fluid chamber of a dialyzer, and a dialysis fluid discharge line which leads from the dialysis fluid chamber of the dialyzer to a drain. The extracorporeal blood circuit comprises an arterial blood line which leads from an arterial puncture point of the patient to the blood chamber, and a venous blood line which leads from the blood chamber to a venous puncture point of the patient. While the dialysis fluid flows through the dialysis fluid chamber of the dialyzer, substances are transported between the blood chamber and the dialysis fluid chamber via the semipermeable membrane of the dialyzer.

The fluid system of the known extracorporeal blood treatment devices, for example dialysis devices, is generally such that a fresh medical treatment fluid at a predetermined flow rate, for example dialysis fluid, flows into the first compartment of the blood treatment unit and used treatment fluid flows from the first compartment of the blood treatment unit into a drain. The fluid system of the known blood treatment devices therefore generally comprises a first flow path having at least one fluid line, which is used as a flow path for supplying a fresh treatment fluid from a fluid source to the first Compartment of the blood treatment unit is formed, and a second flow path having at least one fluid line, which is formed as a flow path for discharging a used treatment fluid from the first compartment of the blood treatment unit to a drain. In order to reduce the risk of contamination, the first and second flow paths of the known blood treatment devices are separated from one another.

The fluid system of the known blood treatment devices generally has additional flow paths which are each required for a particular operating mode. These special operating modes include, for example, filling the blood treatment device with a cleaning agent and / or disinfectant or preparing the blood tubing system for the blood treatment. A special operating mode is also the creation of a flow connection between the first and second flow paths, bypassing the blood treatment unit (bypass) in preparation for the blood treatment or during the blood treatment in the event of a malfunction.

To control the liquid flow, the liquid systems of the known blood treatment devices contain valve devices, which can include one or more shut-off devices, as well as a control unit for controlling the valve device in such a way that the valve device assumes one operating position for one operating mode and another operating position for another operating mode.

The flow paths for the special operating modes comprise an upstream section upstream of a valve device having at least one valve and a downstream section downstream of the valve device, the valve device being designed such that in a first operating position of the valve device there is a fluid connection between the upstream section and the downstream section of the Flow path is established and the fluid connection is interrupted in a second operating position of the valve device. For individual operating modes it may be necessary that the downstream section of the flow path for a particular operating mode with the second flow path in There is a flow connection, so that a liquid, for example dialysis liquid, can flow from the upstream section via the second flow path directly into the drain if the flow connection in the flow path is not interrupted.

A dialysis device which has two separate flow paths in which fresh and used dialysis fluid flow during the blood treatment is known, for example, from EP 2 844 313 B1. To carry out a rinsing process, the fluid system of the dialysis machine has a valve device comprising several shut-off elements.

The invention is based on the object of providing an additional safety measure in order to further reduce the risk of contamination of the blood treatment device as a result of a used liquid flowing into a fresh liquid.

This object is achieved according to the invention with the features of the independent claims. The dependent claims relate to preferred embodiments of the invention.

The blood treatment device according to the invention has a valve device which is provided in a flow path for a special operating mode. The valve device is designed such that in a first operating position of the valve device a fluid connection is established between an upstream section and a downstream section of the flow path for a particular operating mode and the fluid connection is interrupted in a second operating position of the valve device. In addition, the blood treatment device has a pressure-based control device which interacts with a control unit for actuating the valve device and which is designed such that a fluid connection between the upstream section and the downstream section of the flow path for a particular operating mode can only be established if the pressure-based control device has one Establishes operating state in which it is ensured that in the flow path for a particular operating mode liquid flows in the direction of a flow path leading to a drain. This ensures that the liquid in question can only flow into the flow path that leads to the drain, but not into another flow path in which there is fresh treatment liquid.

For the monitoring of the flow direction according to the invention, it is fundamentally irrelevant which liquid line is involved in which liquid flows in the particular operating mode or which liquid is involved.

A preferred embodiment provides that the pressure-based control device an upstream pressure gauge for measuring the upstream pressure in the upstream section of the flow path for a particular operating mode and a downstream pressure meter for measuring the downstream pressure in the downstream section of the flow path and one of the measurement signals of the upstream and downstream Has downstream pressure gauge receiving evaluation unit. The evaluation unit is configured in such a way that the upstream pressure is compared with the downstream pressure, in which case an operating state is inferred in which it is ensured that liquid flows in the direction of the second flow path when the upstream pressure is higher than the downstream pressure.

The control unit and / or evaluation unit can be part of the central control and computing unit of the blood treatment device. The pressure can be measured with a pressure gauge, which is arranged on the upstream or downstream section of the flow path for the particular operating mode, or with a pressure gauge, which is arranged on a liquid line that is in fluid connection with the section in question. Pressure gauges are preferably used which are already provided in conventional blood treatment devices for monitoring the blood treatment.

If it is concluded that there is a faulty operating state, the A wide variety of measures can be taken. For example, an acoustic, visual or tactile alarm can be given in order to notify the medical staff of this and to react accordingly.

The control unit of the valve device or the central control and computing unit of the blood treatment device can be configured in such a way that after receiving a signal from the evaluation unit signaling an incorrect operating state, measures are initiated or method steps are carried out that lead to correct pressure conditions.

Another embodiment provides that the pressure-based control device generates a release signal for the control unit, the control unit being configured such that the valve device is only activated in such a way that the valve device assumes the first operating position when the control unit receives a control signal for setting the special operating mode and receives the release signal. Consequently, the flow connection can only be established by means of the valve device if it is ensured that the liquid cannot get into the part of the liquid system in which the fresh treatment liquid is located.

Another embodiment requires a special structure of the fluid system of the blood treatment device, in which the first flow path comprises a first filter which is divided into a first filter chamber and a second filter chamber by a semipermeable membrane. This filter can serve as a sterile filter for the fresh dialysis fluid. An upstream section of the first flow path connects the liquid source to the first filter chamber of the filter and a downstream section of the first flow path connects the second filter chamber of the filter to an inlet of the first compartment of the blood treatment unit. In this embodiment, the upstream portion of the flow path for the particular mode of operation may be a conduit portion that is in fluid communication with the downstream portion of the first flow path. Since the downstream section of the flow path is in flow connection with the second flow path and thus with the outlet for a particular operating mode, For the special operating state downstream of the sterile filter, a flow connection can be created between the first flow path for fresh treatment liquid and the second flow path for used treatment liquid, bypassing the blood treatment unit (bypass).

In this embodiment, the first pressure gauge can be arranged on the downstream part of the first flow path, and the second pressure gauge can be arranged on the second flow path. An arrangement of the pressure gauges not directly on the upstream and downstream sections of the flow path for a particular operating mode can be useful if pressure gauges are already provided on other fluid lines in the blood treatment device for monitoring the pressure.

Another embodiment, in which the extracorporeal blood circuit comprises a venous blood line and an arterial blood line, provides that the upstream section of the flow path for a particular operating mode is a line section of the venous blood line or a line section in fluid communication with the venous blood line. In this embodiment, the monitoring of the direction of flow allows only a flow of liquid from the venous blood line into the outlet. In this embodiment, the first pressure meter can be arranged on the venous blood line and the second pressure meter can be arranged on the second flow path.

The method according to the invention for operating an extracorporeal blood treatment device provides that before a flow connection is established between an upstream section of a flow path for a particular operating state and a downstream section of the flow path which is in flow connection with the second flow path for a particular operating state, the upstream pressure in the upstream Section and the downstream Wärtige pressure in the downstream section of the flow path is measured for a particular operating condition. The flow communication between the upstream and downstream sections of the A flow path for a particular operating condition is only established when the upstream pressure is higher than the downstream pressure.

In the following, two exemplary embodiments of the invention are explained in more detail with reference to the drawings.

Show it:

Fig. 1 shows an embodiment of the invention

Blood treatment device in a greatly simplified schematic representation, the direction of flow of a liquid being monitored for the control of a first valve device, and

Fig. 2 shows an embodiment of the invention

Blood treatment device in a greatly simplified schematic representation, the direction of flow of a liquid being monitored for the control of a second valve device.

The blood treatment device, in particular a hemo (dia) filtration device, is equipped for operation with a blood treatment unit 1, in particular a dialyzer, which is passed through a semipermeable membrane 2 into a first compartment 3, in particular a dialysis fluid chamber, and a second compartment 4, in particular a blood chamber , is divided.

A blood supply line 5 into which a blood pump leads leads to the inlet 4a of the blood chamber 4

6 is switched, while from the outlet 4b of the blood chamber 4 a blood return line

7 goes off. The blood supply line and discharge line 5, 7 together with the blood chamber 4 form the extracorporeal blood circuit I of the blood treatment device. The fluid system II of the blood treatment device is described below. Blood supply and discharge lines 5, 7 are part of a hose system that is connected to the blood treatment device. The fluid system II of the blood treatment device, in particular the dialysis fluid system, has a dialysis fluid supply line 8, which leads from a dialysis fluid source 9 to an inlet 3a of the dialysis fluid chamber 3, and a dialysis fluid discharge line 10, which branches off from an outlet 3b of the dialysis fluid chamber 3 and leads to an outlet 11 . The dialysis fluid supply line 8 has a first section 8A which leads from the dialysis fluid source 9 to the first filter chamber 12A of a first sterile filter 12 which is divided by a semipermeable membrane 12C into the first filter chamber 12A and a second filter chamber 12B. One chamber 13 A of a balancing device 13 is connected to the first section 8A of the dialysis fluid supply line 8. The second section 8B of the dialysis fluid supply line 8, which leads to the dialysis fluid chamber 3, starts from the second filter chamber 12B of the first sterile filter 12.

To obtain a substituate from the dialysis fluid, the hemo (dia) filtration device can have a second sterile filter 14, which is divided into a first filter chamber 16 and a second filter chamber 17 by a semipermeable membrane 15. The first filter chamber 16 of the second sterile filter 14 is connected to the second section 8B of the dialysis fluid supply line 8. The substituate line is not shown in FIG. 1.

The dialysis fluid discharge line 10 is divided into two sections 10A and 10B, which lead to the drain 11. A dialysis fluid pump 18 is connected in the first section 10A, while an ultrafiltrate pump 19 is connected in the second section 10B. In addition, the other chamber 13B of the balancing device 13 is connected to the second section 10B.

During the blood treatment, fresh dialysis fluid flows from the dialysis fluid source 9 into the dialysis fluid chamber 3 and used dialysis fluid flows out of the dialysis fluid chamber 3 into the drain 11. The dialysis fluid supply line represents a first flow path 8 in which fresh dialysis fluid from the dialysis fluid source 9 to the Dialysis fluid chamber 3 flows, while the dialysis fluid discharge line represents a second flow path 10 in which used dialysis fluid flows from dialysis fluid chamber 3 to drain 11. The flow paths form all sections of the relevant lines, including the components connected into the lines.

A bypass line 20, which leads to the dialysis fluid discharge line 10, branches off from the second section 8B of the dialysis fluid supply line 8, downstream of the second filter chamber 12B of the first sterile filter 11. In the second bypass line 20, a first valve device 21 is connected, which has an electromagnetically actuated shut-off device 21A. The bypass line represents a flow path 20 which is provided for a special operating mode. This operating mode can, for example, be a malfunction, for example the detection of an incorrect composition of the dialysis fluid, which can be detected with a conductivity measurement. In this case, the shut-off element 21 A of the first valve device 21 is opened so that the dialysis fluid can be conducted into the outlet 11 by bypassing the dialyzer 3. To separate the dialyzer 3, a shut-off element 22 is provided upstream and a shut-off element 23 is provided downstream of the dialysis fluid chamber 3.

The line section of the bypass line 20 connected to the dialysis fluid supply line 8 is referred to below as the upstream section 20A and the line section of the bypass line 20 connected to the dialysis fluid discharge line 10 as the downstream section of the flow path 20 for a particular operating mode.

The second filter chamber of the second sterile filter 14 is connected to the dialysis fluid discharge line 10 via a connecting line 24. A second valve device 25, which has an electromagnetically actuatable shut-off element 25A, is connected into the connecting line 10. Upstream of this shut-off device 25A there is a connection piece 26 (port) to which the venous blood line 7A (FIG. 2) can be connected in order to flush the venous blood line 7A. A shut-off element 27, which is closed for the flushing process, is provided upstream of the connection piece 26. Flushing the Venous blood line 7A is a further example of a special operating mode, which will be explained in detail with reference to FIG. 2.

In addition, further lines, shut-off devices or connection pieces (port) can be provided, but these are not important for an understanding of the invention, for example the line 28 and the shut-off devices 29, 30 or the connection piece 35 (port).

The blood treatment apparatus has a control unit 31 which is configured in such a way that the shut-off element 21A or 25A of the first and second valve devices 21, 25 can be opened or closed. The control lines for the electromagnetically actuated shut-off devices 21A and 25A of the first and second valve device 21,

25 are denoted in Figures 1 and 2 with the reference numerals 21 ‘, 25‘. The control unit 31 can also control the other shut-off devices.

The blood treatment device has a control device 32 which has an evaluation unit 32A which receives the measurement signal from a first pressure gauge 33 and the measurement signal from a second pressure gauge 34.

In the embodiment of FIG. 1, the first pressure meter 33 is arranged on the downstream section 8B of the dialysis fluid supply line 8 and measures the pressure Pi in this line section, while the second pressure meter 34 is arranged upstream of the dialysis fluid pump 18 and the ultrafiltrate pump 19 on the dialysis fluid discharge line 10 and measures the pressure P2 in this line section. The two pressure gauges 33, 34 are connected to the control device 32 via signal lines 33, 34 ‘.

During the blood treatment, the first and second shut-off devices 21A, 25B are closed. If a particular operating mode is specified, the control unit 31 receives a control signal in order to open the first or second shut-off element 21A, 25B. In the present exemplary embodiment, it is assumed that the control unit 31 sends a control signal to open the first or second blocking element from a central control and computing unit (not shown) of the blood treatment device, which controls the preparation of the blood treatment device for the blood treatment and the blood treatment.

The evaluation unit 32A forms the difference between the pressure Pi measured with the first pressure gauge 33 and the pressure P2 measured with the second pressure gauge 34 and generates a release signal which the control unit 31 receives when the difference is greater than 0, i.e. H. Pi> P2. The control unit 31 opens the first or second blocking element 21 A or 25 A only when it receives both the corresponding control signal for the first or second blocking element from the central control and computing unit and the release signal from the evaluation unit 32A.

In the event that the control unit 31 for the "bypass" operating mode receives the corresponding control signal, a flow connection between the upstream and downstream sections 20A, 20B of the flow path 20 for this particular operating mode is only established if the pressure Pi> P2, so that it is ensured that fresh dialysis fluid flows from the first flow path 8 into the second flow pad 10 and thus into the outlet 11. If the pressure Pi were <P2, the release signal is not generated, so that there is no risk that used dialysis fluid will pass from the second flow path 10 into the first flow path 8 for fresh dialysis fluid. In FIG. 1, the direction of flow for the dialysis fluid is indicated by arrows when the shut-off element 21 A of the first valve device 21 is open. Other operating states can also be taken into account for bypass operation. For example, no non-physiological dialysis fluid may reach the dialyzer 1 either. If Pi <P2, suitable measures can be taken that the pressure Pi in the first flow path 8 is increased. These measures can be that the shut-off element 22 is closed in the first flow path 8 upstream of the dialysis fluid chamber 3 of the dialyzer 1. When the shut-off element 22 has been closed, so that Pi> P2, the shut-off element 21 can be opened. Instead of the shut-off element 21, the shut-off element 29 can also be opened. FIG. 2 shows the extracorporeal blood treatment device from FIG. 1, the venous hose line 7A being connected to the connection piece 26 for preparing the blood treatment, so that a rinsing liquid can flow through the venous blood line 7A to the outlet 11 when the shut-off device 25A of the second Valve device 25 is open. To flush the venous blood line 7A, the shut-off element 27 is closed upstream of the shut-off element 25A of the second valve device 25. In this exemplary embodiment, the first pressure gauge is a pressure gauge 33 (FIG. 2) which is arranged on the venous blood line 7A and which measures the pressure Pi in this line upstream of the shut-off device 25A of the second valve device 25. As in the first embodiment of FIG. 1, the second pressure gauge is one on the other

Dialysis fluid discharge line 10 arranged pressure gauge 34, which measures the pressure P2 in this line.

In the event that the venous blood line 7A is connected to the connector 26 and the control unit 31 receives the corresponding control signal for the special operating mode “flushing the blood line”, the shut-off element 25A of the second valve device 25 is only opened when the pressure Pi> P2, so that it is ensured that flushing liquid can only flow in the direction of the second flow path 10. In FIG. 2, the direction of flow for the rinsing liquid is indicated by arrows when the shut-off element 25A of the second valve device 25 is open.

In the case of a blood treatment device, only one of the two exemplary embodiments can be implemented. However, it is also possible that both exemplary embodiments are implemented. The flow direction can also be monitored in other “critical flow paths” with the control device according to the invention. In this respect, the two operating modes described are only to be understood as an exemplary embodiment for a “critical flow path”.

Claims

1. Extracorporeal blood treatment device set up for connection to a blood treatment unit (1) which is divided by a semipermeable membrane (2) into a first compartment (3), which is part of a fluid system (II), and a second compartment (4) which Part of an extracorporeal blood circuit (I), the fluid system (II) having a first flow path (8) which has at least one fluid line and is used as a flow path for supplying a fresh treatment fluid from a fluid source (9) to the first compartment (3) of the blood treatment unit (1) and comprises a second flow path (10) which has at least one liquid line and which is designed as a flow path for discharging a used treatment liquid from the first compartment (3) of the blood treatment unit (1) to an outlet (11), and wherein at least one further flow having at least one liquid line flow path (20) is provided for a special operating mode, which has an upstream section (20 A) upstream of a valve device (21) having at least one shut-off element (21A) and a downstream section (20B) in fluid communication with the second flow path (10) the valve device (21), wherein the valve device (21) is designed such that in a first operating position of the valve device a fluid connection between the upstream section (20 A) and the downstream section (20B) of the flow path (20) for a particular Operating mode is established and the fluid connection is interrupted in a second operating position of the valve device, a control unit (31) for activating the valve device (20) in such a way that the valve device (21) assumes the first operating position for the particular operating mode and the second operating position for another operating mode, characterized in that a pressure-based, cooperating with the control unit (31) Control device (32) is provided, which is designed such that a fluid connection between the upstream section (20 A) and the downstream wärti gene section (2 OB) of the flow path (20) for a particular operating mode can only be established if the pressure-based Control device (32) establishes an operating state in which it is ensured that liquid flows in the flow path (20) for a particular operating mode in the direction of the second flow path (10).

2. Extracorporeal blood treatment device according to claim 1, characterized in that the pressure-based control device (32) has an upstream pressure gauge (33) for measuring the upstream pressure in the upstream section (20 A) of the flow path (20) for a special operating mode and a downstream pressure gauge (34) for measuring the downstream pressure in the downstream section (20B) of the flow path for a particular operating mode and an evaluation unit (32A) which receives the measurement signals from the upstream and downstream pressure gauges (33, 34) and which is configured such that the upstream Pressure (Pi) is compared with the downstream pressure (P2), an operating state being inferred in which it is ensured that liquid flows in the direction of the second flow path (10) when the upstream pressure is higher than the downstream pressure.

3. Extracorporeal blood treatment device according to claim 1 or 2, characterized in that the pressure-based control device (32) is configured such that the pressure-based control device (32) generates a release signal for the control unit (31), the control unit being configured such that the Valve device (20) is only controlled in such a way that the valve device assumes the first operating position when the control unit (31) receives a control signal for setting the particular operating mode and the release signal from the pressure-based control device (32).

4. Extracorporeal blood treatment device according to one of claims 1 to 3, characterized in that the first flow path (8) comprises a first filter (12) which passes through a semipermeable membrane (12C) into a first filter chamber (12A) and a second filter chamber ( 12B) is divided, wherein an upstream section (8A) of the first flow path (8) the liquid source (9) with the first filter chamber (12A) of the filter (12) and a downstream section (8B) of the first flow path (8) the second The filter chamber (12B) of the filter (12) connects to an inlet of the first compartment (3) of the blood treatment unit (1), and the upstream section (20A) of the flow path (20) for the special operating mode is a line section which is connected to the downstream Section (8B) of the first flow path (8) is in fluid communication.

5. Extracorporeal blood treatment device according to claim 4, characterized in that the first pressure gauge (33) is arranged on the downstream part (8B) of the first flow path (8), and the second pressure gauge (34) is arranged on the second flow path (10) .

6. Extracorporeal blood treatment device according to one of claims 1 to 5, characterized in that the extracorporeal blood circuit (I) comprises an arterial blood line (5) and a venous blood line (7), the upstream section (20A) of the flow path (20) for the particular operating mode is a line section (7A) of the venous blood line (7) or a line section that is in fluid communication with the venous blood line.

7. Extracorporeal blood treatment device according to claim 6, characterized in that the first pressure gauge (33 (2)) is arranged on the venous blood line (7A), and the second pressure gauge (34) is arranged on the second flow path (10).

8. Extracorporeal blood treatment device according to one of claims 1 to 7, characterized in that the exchange unit is a dialyzer (1) which is divided by a semipermeable membrane (2) into a dialysis fluid chamber (3) and a blood chamber (4).

9. A method for operating an extracorporeal blood treatment device having a blood treatment unit (1) which is divided by a semipermeable membrane (2) into a first compartment (3), which is part of a fluid system (II), and a second compartment (4), which is part of an extracorporeal blood circuit (I), the fluid system (II) having a first flow path (8) which has at least one fluid line and is used as a flow path for supplying a fresh treatment fluid from a fluid source (9) to the first compartment (3) of the Blood treatment unit (1) is formed, and comprises a second flow path (10) having at least one liquid line, which is designed as a flow path for discharging a used treatment liquid from the first compartment (3) of the blood treatment unit (1) to a drain (11) , characterized in that between the establishment of a flow connection an upstream section (20) of a further flow path (20) for a particular operating state and a downstream section (20B) of the flow path (20) for a particular operating state in flow connection with the second flow path (10) upstream pressure (Pi) in the upstream section (20 A) and the downstream wärtigen pressure (P2) in the downstream wärtigen section (2 OB) of the flow path (20) is measured for a particular operating condition and the flow connection is only established when the upstream pressure is higher than the downstream pressure.

10. The method according to claim 9, characterized in that the first flow path (8) comprises a first filter (12) which is divided by a semipermeable membrane (12C) into a first filter chamber (12A) and a second filter chamber (12B), wherein an upstream section (8A) of the first flow path (8) the liquid source (9) with the first filter chamber (12A) of the filter (12) and a downstream section (8B) of the first flow path (8) the second filter chamber (12B) of the Filter (12) connects to an inlet (3a) of the first compartment (3) of the blood treatment unit (1), whereby a liquid flow over the flow path (20) for a particular operating mode from the downstream section (8B) of the first flow path (8) the second flow path (10) is established only when the upstream pressure (Pi) in the upstream section (20 A) is higher than the downstream pressure (P2) in the downstream section (20B) of the flow is ungspfads (20) for a particular operating mode.

11. The method according to claim 10, characterized in that the upstream pressure (Pi) with one on the downstream section (20 A) of the first flow path (8) arranged pressure gauge (33) and the downstream pressure (P2) with one on the second Flow path (10) arranged pressure gauge (34) is measured.

12. The method according to any one of claims 9 to 11, characterized in that the extracorporeal blood circuit (I) comprises an arterial blood line (5) and a venous blood line (7), wherein a liquid flow over the flow path for the particular operating state of the venous blood line (7A) to the second flow path (10) is established only when the upstream pressure (Pi) in the upstream section (20 A) is higher than the downstream pressure (P2) in the downstream section (20B) of the flow path (20) for a particular operating condition is.

13. The method according to claim 12, characterized in that the upstream pressure (Pi) with a pressure gauge (33 ') arranged on the venous blood line (7A) and the downstream pressure (P2) with one arranged on the second flow path (10) Pressure gauge (34) is measured.

14. The method according to any one of claims 9 to 13, characterized in that the exchange unit is a dialyzer (1) which is divided by a semipermeable membrane (2) into a dialysis fluid chamber (3) and a blood chamber (4).

15. The method according to any one of claims 9 to 14, characterized in that the liquid which flows via the flow path (20) for a particular operating state is dialysis liquid or a rinsing liquid.