A feasibility study of a filtration type autotransfusion device

This paper describes a feasibility study of a disposable autotransfusion device for blood salvage during surgery. The goal was to concentrate hemolyzed blood at 20% hematocrit to 50% while reducing the plasma free hemoglobin concentration from 10 to 1.5 g/l. The device should have a total membrane area of less than 0.6 m2 and should be able to process ten 500 ml blood bags. The processing time for each blood bag should not exceed 5 min. The basic idea was to use several polypropylene hollow fibre plasma filters of 0.1 m2 in series with saline addition between them. Since the mean pore size is 0.5 microns, anticoagulant and plasma hemoglobin can pass freely across the membrane and their concentration is reduced by dilution. The process was first modelled using mass balance equations for red blood cells and plasma hemoglobin in order to find the best device configuration (number of filters and dilutions). It was found that a three filter system could theoretically meet the requirements, if the last filter had a larger surface area (0.3 m2). Some experiments permitted us to prove the validity of this model and to define fully the third filtration stage. Finally, it was shown that the treatment of a 500 ml blood bag required three filtration stages (whose surface areas were respectively 0.1, 0.1 and 0.3 m2) and the use of 750 ml of saline solution added between the filters. This configuration also offers the possibility of using a vacuum driving force instead of pumps, so that the device becomes completely disposable.