Method for Blowing Free a Wetted Hydrophobic Filter, and Device for Carrying Out the Method

Abstract

This invention relates to a method for clearing a wetted hydrophobic filter, in which in a first step the air permeability of the hydrophobic filter is monitored and in which in a second step the hydrophobic filter is cleared by means of a connected air pump, if it is detected that the hydrophobic filter is clogged. Furthermore, the invention relates to an apparatus for performing this method.

Description

This invention relates to a method of clearing a wetted hydrophobic filter and an apparatus for performing this method.

It is known already to connect a pressure sensor in an extracorporeal blood circulation via a tube conduit branching off from this blood circulation, in order to measure the pressure in this blood circulation. In principle, this connecting conduit can branch off at any point of the blood circulation, for instance from a venous air separation chamber present in the blood circulation.

In the branching tube, to which the pressure sensor is connected, a certain amount of air is included, by means of which the pressure is transferred to the pressure sensor. Usually, the pressure sensor is integrated in a blood treatment machine. To prevent the undesired advancement of blood up to the blood treatment machine, at least one hydrophobic protective filter is disposed in the conduit. Together with the remaining set of blood tubes of the extracorporeal blood circulation, this hydrophobic filter is discarded upon completion of a blood treatment.

During operation of the extracorporeal blood circulation, it can occur that the hydrophobic filter is wetted by the blood and thereby is at least partly clogged unilaterally. This results in a—partly creeping—impairment of the operability of the pressure measurement. This problem is discussed in EP-A-0 330 761. To be able to detect the malfunction, according to this teaching, the pressure sensor should not only detect the static pressure, but there should also be detected the pressure fluctuations present in the extracorporeal blood circulation. As far as the pressure sensor system becomes less sensitive, it is not only the static pressure which no longer is indicated correctly, but the periodic pressure fluctuations no longer are indicated either. If the pressure fluctuations no longer can regularly be detected by the pressure sensor, it can be concluded that the hydrophobic filter is clogged to such an extent that a sufficiently precise pressure measurement no longer is possible.

As far as the user recognizes this problem, he can destroy the filter in a controlled way and replace the same by a second filter. In general, however, the hydrophobic filter is connected with the entire set of blood tubes, so that a filter change only is possible with a considerable effort.

From U.S. Pat. No. 3,964,479 there is already known an extracorporeal blood circulation, in which a pressure sensor is connected to a branching point of an air separation chamber provided in the blood circulation. The teaching of this U.S. patent deals with the problem of adjusting liquid levels inside the air separation chamber at a desired height. For this purpose, an air pump is branched off from the conduit between the air separation chamber and the pressure sensor, in which a hydrophobic filter is also provided according to the known solution, which air pump serves to set the liquid level in the air separation chamber at a certain level. For this purpose, air can be pumped into the air separation chamber or be withdrawn from the same.

It is the object of the present invention to propose a method and an apparatus which upon detection of a clogged filter eliminates such malfunction automatically, if possible, and at least leads to the fact that the hydrophobic filters must be replaced less frequently.

In accordance with the invention, this object is solved by the combination of the features of claim 1. In accordance with the invention, there is created a method for clearing a wetted hydrophobic filter in an extracorporeal blood circulation, wherein the extracorporeal blood circulation includes an air separation chamber to which a pressure pick-up and an air pump are connected via a conduit, the hydrophobic filter being disposed within said conduit. The method of the invention at least comprises the following steps:

• • monitoring the air permeability of the hydrophobic filter, and
  • clearing the hydrophobic filter by means of the connected air pump, if it is detected that the hydrophobic filter is clogged.

Monitoring the air permeability of the hydrophobic filter can for instance be effected analogous to the above-mentioned teaching in accordance with EP-A-0 330 761. If an at least partial clogging of the hydrophobic filter is detected, the connected air pump is actuated via a corresponding control such that the hydrophobic filter is cleared.

A preferred aspect of this teaching of the invention is disclosed in the sub-claims.

Accordingly, the air permeability of the hydrophobic filter can be monitored by means of the pressure pick-up.

While the hydrophobic filter is cleared, a clamp disposed in the extracorporeal blood circulation downstream of the air separation chamber can be opened on the one hand, and on the other hand valves can be opened, which are provided in the connecting conduits to the air pump and to the pressure pick-up.

Advantageously, the course of pressure over time is adopted by the air pump during the clearing process.

When the change in pressure per unit time, i.e. the rate of change in pressure, exceeds a specified limit value, an alarm signal for replacing the hydrophobic filter is produced. Then, clearing definitely is not easily possible. It should be considered that the blow rate of the air pump cannot be increased to any extent, as in a borderline case the bursting pressure of the hydrophobic filter will be exceeded.

However, if the change in pressure per unit time does not exceed the specified limit value, the valve in the supply conduit of the air pump can advantageously be closed again upon clearing the filter.

In accordance with another advantageous aspect of the invention, the filling level of the blood in the air separation chamber is monitored by means of a filling level detector during the clearing process. It can thus be prevented that the filling level decreases too much and, in an extreme case, air gets into the tube system and hence into the patient.

Advantageously, the air pump is actuated by means of a control and monitoring program which also records the pressure values over time.

An apparatus for performing the method of the invention is disclosed in claim 9. This apparatus includes an air separation chamber disposed in an extracorporeal blood circulation, to which a pressure pick-up and an air pump for adjusting the filling level in the air separation chamber are connected via a conduit, a hydrophobic filter being provided in said conduit. For performing the aforementioned method, this apparatus includes a control and monitoring unit by means of which the air pump can be actuated for clearing the hydrophobic filter, while at the same time the pressure values per unit time can be recorded and monitored.

Furthermore, the apparatus for performing the method of the invention preferably includes an alarm device for producing an alarm for the case that the hydrophobic filter cannot be cleared.

Further features, details and advantages of the invention will be explained with reference to the embodiment illustrated in the only FIGURE. The only FIGURE shows a schematic representation of a part of an extracorporeal blood circulation.

In the representation as shown in the FIGURE, only part of a blood-carrying tube 10 of an extracorporeal blood circulation is shown, which extends from the top into a conventionally designed air separation chamber 12 and then extends from the lower end of the air separation chamber. The air separation chamber can be disposed for instance in the blood return conduit (venous blood conduit) of the extracorporeal blood circulation. Below the air separation chamber 12, a pinch clamp 14 is disposed in the blood-carrying tube 10. For detecting the filling level of the blood inside the air separation chamber 12, a filling level detector 16 is mounted on the air separation chamber.

Via an air-carrying tube 18, the air separation chamber 12 is connected with a pressure sensor 20. The pressure sensor 20 is disposed inside a dialysis device, whose outer wall is only indicated here by the line 22 for the sake of simplification. In the conduit 18 between the air separation chamber 12 and the pressure sensor 20 a hydrophobic filter 24 is disposed still outside the dialysis device.

Inside the dialysis device, a conduit 26 leading to an air pump 28 branches off from the air-carrying conduit 18. Between the branching point to the conduit 26 and the pressure sensor 20, the conduit 18 includes a controllable valve 30. The air-carrying conduit 26 likewise includes a controllable valve 32.

During the usual operation of the extracorporeal blood circulation, blood is dripping from the conduit 10 into the air separation chamber 12. The filling level in the air separation chamber 12 is monitored by means of the filling level detector 16. If it falls below a desired level, the height of the filling level of the blood in the air separation chamber 12 can be adjusted here by means of the air pump 28 or the clamp 14. During the operation of the extracorporeal blood circulation, the pressure is determined by the pressure sensor 20. Via a measurement routine, as it is known for instance from EP-A-0 330 761, it can be detected here whether the hydrophobic filter 24 is at least partly clogged due to wetting with blood. If a partial clogging is detected, the valves 30 and 32 are opened (unless the valve 30 has already been open), and by means of the air pump 28 an excess pressure is produced, in order to clear the hydrophobic filter 24. During such clearing, the pinch clamp 14 is opened at the same time (unless it has already been open), in order to avoid an excess pressure in the system.

While air is supplied to the hydrophobic filter 24, the course of pressure over time is monitored by means of the pressure sensor. Should the pressure rise too fast, this indicates a fundamental problem inside the filter, which cannot be overcome by clearing by means of the air pump 28. In this case, an alarm signal is activated by the control and monitoring means, which is provided to the user by a corresponding alarm device. In the case of an alarm, the hydrophobic filter 24 must be replaced.

Should the increase in pressure be small enough, clearing is possible. In this case, it must merely be ensured by means of the level detector 16 that the blood level inside the venous air separation chamber 12 does not decrease too much, in order to safely prevent the penetration of air into the tube system 10 inside the air separation chamber 12.

Claims

1. A method of clearing a wetted hydrophobic filter in an extracorporeal blood circulation with an air separation chamber to which a pressure pick-up and an air pump are connected via a conduit, the hydrophobic filter being disposed in said conduit, comprising the following steps: monitoring the air permeability of the hydrophobic filter, andclearing the hydrophobic filter by means of the connected air pump, if it is detected that the hydrophobic filter is clogged.

2. The method as claimed in claim 1, characterized in that the air permeability of the hydrophobic filter is monitored by means of the pressure pick-up.

3. The method as claimed in claim 1, characterized in that while clearing the hydrophobic filter, a clamp disposed in the extracorporeal blood circulation downstream of the air separation chamber is opened on the one hand, and on the other hand valves are opened, which are provided in the connecting conduits to the air pump and to the venous pressure pick-up.

4. The method as claimed in claim 3, characterized in that the course of pressure over time is adopted by the air pump during the clearing process.

5. The method as claimed in claim 4, characterized in that for the case that the change in pressure per unit time exceeds a specified limit value, an alarm signal is produced for replacing the hydrophobic filter.

6. The method as claimed in claim 4, characterized in that for the case that the change in pressure per unit time does not exceed a specified limit value, the valve in the supply conduit of the air pump is closed again upon clearing the filter.

7. The method as claimed in claim 1, characterized in that during the clearing process, the filling level of the blood in the air separation chamber is monitored by means of a filling level detector.

8. The method as claimed in claim 1, characterized in that the air pump is actuated by means of a control and monitoring program which also records the pressure values over time.

9. An apparatus for performing a method as claimed in claim 1, comprising an air separation chamber disposed in an extracorporeal blood circulation, to which a pressure pick-up and an air pump are connected via a conduit, a hydrophobic filter being disposed in said conduit, characterized bya control and monitoring unit by means of which the air pump can be actuated for clearing the hydrophobic filter, while at the same time the pressure values per unit time can be recorded and monitored.

10. The apparatus as claimed in claim 9, characterized by an alarm device for producing an alarm for the case that the hydrophobic filter cannot be cleared.