1. Field of the Invention
The present invention relates to a blood processing filter for removing undesirable components such as aggregates and leukocytes from blood. In particular, the present invention relates to a precise and disposable blood processing filter for removing microaggregates and leukocytes which may cause side effects from whole blood preparations, erythrocyte preparations, thrombocyte preparations, blood plasma preparations and the like for blood transfusion, as well as a method for priming the blood processing filter.
2. Related Background Art
It is becoming common for whole blood collected from a donor to be separated into blood component preparations such as an erythrocyte preparation, a thrombocyte preparation, and a blood plasma preparation and stored for transfusion. Since microaggregates and leukocytes included in these blood preparations cause various side effects during blood transfusion, the number of occasions for removing these undesirable components before blood transfusion has been increasing. The need for leukocyte removal has widely been recognized particularly in recent years. Legislation regarding removal of leukocytes from all kinds of blood preparations for blood transfusion before being used for transfusion has been introduced in an increasing number of countries.
The most common method of removing leukocytes from blood preparations is by processing blood preparations using a leukocyte removal filter. Conventionally, in many cases blood preparations processed using a leukocyte removal filter have been processed at the bedside when blood transfusion is performed. In recent years, however, to improve quality control of leukocyte-free preparations and efficiency of leukocyte removal operations, it is more common, particularly in developed countries, to process the blood preparations in blood centers before storing the blood preparations. Hereinafter, a leukocyte removal performed before storage is referred to as a “pre-storage leukocyte removal”.
A blood collection-separation set, typically consisting of two to four flexible bags, a tube connecting these bags, an anticoagulant, an erythrocyte preservation solution, a blood collection needle, and the like has been used for collecting blood from a donor, separating the blood into several blood components, and storing the blood components. A system in which a leukocyte removal filter is incorporated into such a blood collection-separation set has been widely used as an optimum system for the above-mentioned “pre-storage leukocyte removal”. Such a system is called a “closed system” or an “integrated system” or the like. Such systems are disclosed in Japanese Patent Laid-Open No. 1-320064, International Publication No. WO 92/020428 and the like.
Conventionally, a filter element made from nonwoven fabric or a porous body packed in a hard container of polycarbonate or the like has been widely used as a leukocyte removal filter. However, because, in case of the hard container, the container has a low level of air permeability, there is the problem that it is difficult to apply steam sterilization, which is widely used as a sterilization process in blood collection-separation sets. In one type of closed system, leukocytes are first removed from the whole blood preparation after collecting the blood. Subsequently, after the leukocyte removal filter is separated, the leukocyte-free blood is centrifuged for separation into various components. In another type of closed system, the whole blood is first centrifuged to be divided into various blood components, and then the leukocytes are removed. In the latter system, the leukocyte removal filter is also centrifuged together with the blood collection-separation set. At such time, a hard container may damage bags and tubes, or the hard container itself may not withstand the stress and may break during centrifugation.
To solve these problems, flexible leukocyte removal filters have been developed in which the container is made of a material having excellent flexibility and steam permeability that is the same as or similar to the material used for the bags of the blood collection-separation set, and in fact blood processing filters in which a flexible container is directly welded to a filter element and the like are known (see Japanese Patent Laid-Open No. 7-267871 and International Publication No. WO 95/017236). According to this kind of conventional blood processing filter, for example, a flexible container is formed using a sheet-like material having flexibility, and an internal space of the flexible container is divided into one side and another side by a filter element. Ports that serve as an inlet and an outlet for blood are respectively provided on the one side and the other side into which the flexible container is divided by the filter element.
However, according to the conventional leukocyte removal filter, in many cases the one side and the other side into which the flexible container is divided by the filter element are substantially the same shape and have the same capacity, and it can not be said that sufficient consideration has been given to filter performance in relation to suppressing blockage of the filter element that results from the interrelationship between the one side and the other side of the flexible container and to preventing an air block occurring when priming and the like.