METHOD FOR VENTING A DIALYZER

Abstract

The invention relates to a method for venting a dialyzer which has a dialyzate chamber, a blood chamber and a semi-permeable dialyzer membrane separating these two chambers, wherein an overpressure is generated in the dialyzate chamber with respect to the blood chamber for removing air inclusions lying at the surface of the membrane at the dialyzate chamber side after a filling of the dialyzate chamber and before a filling of the blood chamber.

Claims

1. A method for venting a dialyzer (3) which has a dialyzate chamber (4), a blood chamber (5) and a semipermeable dialyzer membrane (6) separating these two chambers, characterized in that an overpressure is generated in the dialyzate chamber (4) with respect to the blood chamber (5) for removing air inclusions (50) lying at the surface of the membrane (6) at the dialyzate chamber side after a filling of the dialyzate chamber (4) and before a filling of the blood chamber (5).

2. A method in accordance with claim 1, characterized in that the overpressure lies in the range up to 2 bar, preferably in the range between 50 and 500 mmHg, preferably in the range between 140 and 220 mmHg, and further preferably in the range between 175 and 195 mmHg.

3. A method in accordance with claim 1, characterized in that the blood chamber (5) is vented toward the environment during the generation of the overpressure.

4. A method in accordance with claim 1, characterized in that the dialyzate chamber (4) is connected to a fluid-conducting system (1) at the infeed and/or return side during the carrying out of the method and is preferably integrated into the dialyzate circuit (1) of a dialysis machine, wherein provision is preferably made that the overpressure is generated by the closing of a valve (8) arranged at the return side of the dialyzate chamber (4) and the simultaneous conveying of further fluid from the feed side (1a) of the fluid-conducting system (1) into the dialyzate chamber (4).

5. A method in accordance with claim 1, characterized in that the pressure build-up is stopped after reaching a predefined overpressure value (p.sub.MAX) in the dialyzate chamber (4), preferably by stopping the pump (29).

6. A method in accordance with claim 1, characterized in that the overpressure in the dialyzate chamber (4) is maintained over a venting time period (t.sub.VENT) after the stopping of the pressure build-up, preferably by keeping the valve (8) closed.

7. A method in accordance with claim 1, characterized in that the pressure prevailing in the dialyzate chamber (4) and/or its development during the pressure build-up and/or in the venting time period (t.sub.VENT) is measured.

8. A method in accordance with claim 7, characterized in that a characteristic of the measured pressure development in the venting time period (t.sub.VENT) is used to selectively initiate a repeat of the method or a continuation of the priming procedure, for example a flushing procedure of the dialyzate chamber (4) and/or a filling of the blood chamber (5).

9. A method in accordance with claim 7, characterized in that a characteristic related to the measured pressure development during the pressure build-up is compared with a corresponding stability criterion which is representative for the integrity of the dialyzer membrane (6) and/or the integrity of interfaces of the dialyzate chamber (4) with the fluid-conducting system (1); and in that a warning signal is emitted on a deviation of the characteristic from the stability criterion.

10. A dialysis machine having a dialyzate circuit (1) and a dialyzer (3) which has a dialyzate chamber (4) integrated into the dialyzate circuit (1), a blood chamber (5) and a semipermeable dialyzer membrane (6) separating these two chambers, characterized in that, the dialysis machine has a control unit on which an algorithm is stored for carrying out a method in accordance with claim 1.

Description

[0037] Further details and advantages of the invention result from the following embodiment described with reference to the Figures. There are shown in the Figures:

[0038] FIG. 1: a schematic representation of the fluid-conducting system of a dialysis machine; and

[0039] FIG. 2: the time development of the fluid pressure in the dialyzate chamber during the carrying out of a method in accordance with the invention.

[0040] FIG. 1 shows a schematic representation of the fluid-conducting system of a dialysis machine.

[0041] The fluid-conducting system comprises a dialyzate circuit 1, a blood circuit 2 and a dialyzer 3. The dialyzer comprises a dialyzate chamber 4, a blood chamber 5 and a semipermeable membrane 6 which separates the dialyzate chamber 4 and the blood chamber 5 from one another. In the capillary dialyzers which are typically used, the blood chamber 5 is formed by the totality of the inner volumes of the hollow fibers and the dialyzate chamber 4 is formed by the inner space of the dialyzer housing surrounding the hollow fibers.

[0042] The flow direction of the priming fluid or dialysis fluid in the dialyzate circuit is symbolized by the arrows 1c in the Figure.

[0043] A feed valve 7 is located in the feed line 1a of the dialyzate circuit 1 and a return valve 8 is located in the return line 1b. The two valves are arranged in the direct vicinity of the dialyzer 4 in the embodiment shown and each represent the closest actuator. A feed pressure sensor 9 is arranged in the feed line 1a of the dialyzer 3 and serves the determination of the fluid pressure at the feed side andin the case of a closed return valve 8of the fluid pressure in the dialyzate chamber 4 of the dialyzer 3.

[0044] The feed line 1a furthermore comprisesin the named order in the flow directionthe feed side of a balance chamber 10, a venting valve 11, a sterile filter 12, a conductivity and temperature measurement arrangement 13 and a maintenance valve 14 for any carrying out of a pressure maintenance test. The feed pressure sensor 9 is arranged between the maintenance valve 14 and the feed valve 7.

[0045] The return line 1b is divided into three between a first branch point 15 and a second branch point 16, wherein a first branch 17 comprisesin the named order in the flow directiona return pump 18 and the return side of the balance chamber 10. A second branch 19 comprises an ultrafiltration pump 19a and does not pass through the balance chamber 10. A third branch 20 comprises a simple auxiliary valve 21. A return pressure sensor 22 is arranged in front of the branch point 15. A blocking valve 23 is arranged after the second branch point 16.

[0046] A bypass line 24 comprising a bypass vale 25 is furthermore arranged between the feed line 1a and the return line 1b. The bypass line 24 branches off from the feed line 1a between the measurement arrangement 13 and the maintenance valve 14 and opens into the return line 1b between the return valve 8 and the return pressure sensor 22.

[0047] A retentate line 26 having a retentate valve 27 is furthermore provided and connects the retentate side of the sterile filter 12 to the return line 1b. The retentate line opens into the return line 1b between the bypass line 24 and the return pressure sensor 22.

[0048] A supply pump which is not shown in any more detail in the Figure and which is arranged in the feed line 1a at the feed side of the balance chamber 10 serves to convey the priming fluid or dialyzing fluid into the feed line 1a and the dialyzer and to build up pressurewithin the framework of the method in accordance with the inventionin the dialyzate chamber.

[0049] The blood circuit 2 comprises an arterial line 2a and a venous line 2b, with the dialyzer 3 being connected in the counter-flow principle. The arterial line 2a comprisesin the named order in the flow directionan arterial pressure sensor 28, a blood pump 29 and, optionally, an arterial bubble trap 30. The venous line 2b comprisesin the named ordera venous bubble trap 30a plus a bubble detector 31 and a venting apparatus 32 as well as a venous clamp 33. The venting apparatus 32 comprises a venting line 34, a venting pressure sensor 35 and a venting valve 36.

[0050] The dialyzate chamber 4 of the dialyzer 3 is filled within the framework of a known process before carrying out the method in accordance with the invention for removing air inclusions. In the embodiment shown, the filling takes place within the framework of an online process, with the dialyzer 3 being connected to the dialyzate circuit 1 of the dialysis machine. Alternatively, the filling can also take place using a saline bag.

[0051] The method starts after the filling of the dialyzate chamber 4 and before the filling of the blood chamber 5. The blood circuit 2, including the blood chamber 5, is still filled with air on the carrying out of the method.

[0052] The feed valve 7 is first held open and the return valve 8 is closed within the framework of the method. A pressure-controlled filling program is started which conveys additional priming fluid into the dialyzate chamber 4 through the feed line 1a using the supply pump. Since the return valve 8 is closed, an overpressure builds up in the dialyzate chamber 4 with respect to the blood chamber 5in which environmental pressure prevails.

[0053] The overpressure arising in relation to the environmental pressure is detected using the feed pressure sensor 9. Once a defined overpressure of, for example, 150 mmHg has been reached, the fluid infeed is stopped and the pressure development or pressure loss measured at the feed pressure sensor 9 is observed during a venting time period. If air flows out of the dialyzate chamber 4 through the membrane 6 into the blood chamber 5, the overpressure in the dialyzate chamber 4 reduces fast again since the dry membrane 6 represents a relatively small flow resistance for air.

[0054] The air bubbles are drawn with the reference numeral 50 in FIG. 1 and the flow direction from the dialyzate chamber 4 into the blood chamber 5 is indicated by an arrow 51.

[0055] So that no counter-pressure to the atmosphere builds up in the blood chamber 5, the blood chamber 5 is vented toward the atmosphere, for example by means of the ends of the arterial line 2a and/or the venous line 2b or by means of the venting line 34 with an open venting valve 36.

[0056] If the overpressure drops fast in the dialyzate chamber 4, it is built up again. If the overpressure in the dialyzate chamber 4 does not drop or only drops very slowly, this means that there is no longer any residual air in the dialyzate chamber 4 or the initially present residual air has already been largely pressed into the still empty blood chamber 5.

[0057] A time development of the liquid pressure in the dialyzate chamber 4 determined experimentally within the framework of an experiment is shown in FIG. 2. The fluid pressure in the dialyzate chamber 4 measured at the feed pressure sensor 9 is entered in mmHg on the ordinate in the diagram and the time in minutes is entered on the abscissa. At the time T.sub.INIT, the return valve 8 was closed and the supply pump was operated further until an overpressure p.sub.MAX of 185 mmHg was built up in the dialyzate chamber. This over pressure was completely depleted again relatively fast within a venting time period t.sub.VENT of approximately 2 to 3 minutes due to the passage of residual air from the dialyzate chamber 4 into the blood chamber 5.

[0058] This behavior is also facilitated by hydrophobic properties of the membrane. As long as the blood chamber 5 of the dialyzer 3 has not yet been filled and is therefore dry, the membrane has a large flow resistance for the aqueous priming fluid.

[0059] In addition to a venting, the method in accordance with the invention can also be used by additional parameterization to determine the integrity of the dialyzer membrane 6 or of the interfaces of the dialyzer 3 with the feed line 1a and the return line 1b. A stability criterion is defined here which is, for example, the maximum fluid supply which is required for building up a specific pressure. If this stability criterion of the volume restriction is not observed, conclusions can be drawn from this on a possible rupture of the membrane 6 or on a leaking interface.