An in vitro comparison of six microaggregate blood filters.

The latest models of six blood microfilters were tested by filtering large amounts of pooled blood at various driving pressures. For determination of the amount and size of microaggregates in stored blood, a simple method was developed, based on consecutive nylon screens. The amount of aggregates was also determined by a modification of the screen filtration pressure method. Filtration efficiency was tested by transfusing blood from the same pool through each of the microfilters. The Pall (SQ40KL) filtered only particles with a diameter greater than 40 micrometers. Small aggregates passed also through Bentley (PFF-100). The Biotest (MF10B) filter removed large aggregates efficiently, but some small particles were not filtered. Fenwal (4C2423), Swank (6010-3) and Intersept (HRI8137-00) were the most effective filters. All filters were also tested by pressure transfusion of pooled blood (9 units, 21 days old). The efficiency of Biotest, Pall and especially Bentley improved considerably during the transfusion. Bentley and Fenwal had the highest capacities. A high flow rate was maintained with Pall, but small aggregates were not removed by this filter. Intersept, Swank and Biotest became occluded rapidly. Filtration of four units through Intersept released 2218-2454 mg of hemoglobin from the erythrocytes.