Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
1999-07-19
2001-02-13
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C073S038000, C073S040000, C210S090000, C210S646000, C210S741000
Reexamination Certificate
active
06187207
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of verifying proper replacement of a used filter that is divided by a membrane into two chambers and that is arranged in the fluid system of a device for extracorporeal treatment of blood. In addition, the present invention relates to a device for extracorporeal treatment of blood with a fluid system containing at least one filter divided by a membrane into a first and a second chamber, so that proper filter replacement is verifiable.
DESCRIPTION OF RELATED ART
To remove substances usually eliminated with the urine and for removal of fluids, various methods of extracorporeal treatment or purification of blood are used to treat chronic renal failure. In hemodialysis, a patient's blood is purified outside the patient's body in an artificial kidney known as a dialyzer. The dialyzer has a blood chamber and a dialysis fluid chamber separated by a semipermeable membrane. During the treatment, the patient's blood flows through the blood chamber on one side of the membrane. To effectively purify blood of substances usually eliminated with the urine, fresh dialysis fluid flows continuously through the dialysis fluid chamber.
Diffuse mass transport is the predominant mechanism in hemodialysis (HD), while convective mass transport through the membrane dominates in hemofiltration (HF). Hemodiafiltration (HDF) is a combination of the two methods. In hemo(dia)filtration, a portion of the serum removed through the membrane is replaced by a sterile replacement fluid added to the extracorporeal blood circuit, either upstream from the dialyzer (predilution) or downstream from the dialyzer (postdilution).
In current devices for hemo(dia)filtration the dialysis fluid is prepared online from fresh water and an electrolyte concentrate, and the replacement fluid is prepared online from the dialysis fluid. To ensure that the dialysis fluid and replacement fluid prepared online are sterile and free of pyrogens, the fluids are passed through filters arranged in the fluid system of the hemo(dia)filtration machine. These filters are divided into two chambers by a microbe-retaining membrane. Such a device with two filters arranged in the dialysis fluid system is known from German Patent 34 44 671 C2.
German Patent 34 48 262 C2 describes a method of verifying that the filters of the hemo(dia)filtration machine known from German Patent 34 44 671 C2 are leakproof. The filter integrity test is performed using a pressure retaining test, with a partial vacuum being established in one of the two chambers of the filter. The pressure retaining test is based on the fact that when the membrane of the filter is wetted with a fluid, it is essentially impermeable to gases. An increase in pressure in the chamber can be detected during the pressure retaining test only when there is a defect.
German Patent 34 42 744 A1 describes a membrane integrity test for a used dialyzer, where the chambers of the dialyzer are filled with air, and equalization of pressure across the wetted membrane is observed.
Manufacturers of known sterile filters for hemo(dia)filtration machines suggest the replacement of filters at certain intervals, for reasons of safety. There are known hemo(dia)filtration machines which notify the user automatically when it is necessary to change the filter. To increase safety, the known hemo(dia)filtration machines also provide for manual confirmation of replacement of the filter by the user. However, this safety device cannot prevent the user from simply confirming that the filter has been replaced, without having actually replaced the filter.
SUMMARY OF THE INVENTION
The present invention is directed to a device and method for verifying proper replacement of a used filter in the fluid system of a machine for extracorporeal treatment of blood that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatus and method particularly pointed out in the written description and claims hereof, as well as the appended drawing.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention is a method for determining if a filter in the fluid system of a device for extracorporeal treatment of blood has been replaced with a new filter, that includes measuring whether a membrane of the filter that divides the filter into a first and a second chamber is permeable to gas and, in the event the membrane is permeable to gas, concluding that the filter has been replaced.
In another aspect, the invention is a device for extracorporeal treatment of blood, that includes at least one filter divided by a membrane into a first chamber and a second chamber, disposed along a fluid system of the device, and means for measuring a gas permeability of the membrane of the at least one filter. The device also includes means for determining whether the at least one filter has been replaced by a corresponding new filter, based on the gas permeability of the membrane.
One object of the present invention is to provide a method that will make it possible to ascertain with a high degree of certainty whether a used filter has been replaced by a new filter. In addition, another object of the present invention is to provide a device for extracorporeal treatment of blood that includes a device for verifying with a high degree of certainty whether proper replacement of the filter was carried out.
It is assumed in the present invention that the membrane of a new filter is dry, while the membrane of a used filter is wetted with fluid. A pressure retaining test is performed to verify the proper replacement of the filter. Verification is undertaken to determine whether the membrane of the filter is permeable to gas. If the membrane is impermeable to gas, it is concluded that the membrane is wetted with fluid, and that the filter installed is a used filter.
By using the pressure retaining test, proper replacement of all filters arranged in the fluid system of the machine for extracorporeal treatment of blood can be tested. This includes the filters for supplying sterile dialysis fluid and replacement fluid as well as the dialyzer filter itself.
The gas permeability of the membrane of the filter can be verified by a vacuum test or an excess pressure test. Preferably, a section of the fluid system including the first chamber of the filter and another section including the second chamber of the filter are isolated. Gas is then directed into one of the two sections to build up an excess pressure, which is monitored. The other section of the fluid system is then opened again, and if there is a pressure drop in the isolated section, it is deduced that the filter has been properly replaced. With this system it is also possible to verify whether an excess pressure can be built up and maintained in the isolated section of the fluid system that includes one of the two chambers. If that is the case, the filter is a used filter whose membrane is wetted with fluid.
The pressure drop per unit of time, or rate of pressure drop, is preferably compared to a predetermined limit value. If this limit value is exceeded, it can be deduced that the filter has been properly replaced. This ensures that it will be possible to differentiate between a pressure drop due to the fact that the membrane of the filter is not wetted with fluid, and the more minor pressure drop also detected with a membrane wetted with fluid over a long period of time.
To build up an excess pressure, it is preferable to direct atmospheric air into one of the two sections of the fluid system, where the excess pressure can be established with an air pump. To prevent microorganisms from entering the fluid sy
Drodge Joseph W.
Fresenius Medical Care Deutschland GmbH
Kenyon & Kenyon
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