Proceedings: A preliminary study of microfilters: do they have a role to play during blood transfusion?

R. B. BULEY, AND JEAN LUMLEY Department of Anaesthetics, Royal Postgraduate Medical School, Ducane Road, London Many factors have been incriminated in the aetiology of the post-traumatic pulmonary insufficiency syndrome. One factor, which can possibly be avoided, is the deposition in pulmonary capillaries of cellular debris of microemboli following massive transfusion. Swank (1961) and McNamara (1971) have demonstrated that cellular degradation products appear in increasing amounts as stored blood ages. Quantitively this debris is measured by the screen filtration pressure or s.f.p. Reul (1973) postulated that the use of microfilters during blood transfusion can diminish the amount of cellular debris presented to the lung. The efficiency of three microfilters employing surface or depth filtration principles was assessed under simulated clinical conditions in the laboratory: a microfilter being a filter with a significantly reduced pore size when compared with a standard filter. One-, 2and 3-week-old blood stores in citrate phosphate dextrose solution was transfused at a constant pressure of 250 mm Hg using a Fenwal BD4 pressure infusor. The microfilter under investigation was placed in line with a routine Baxter BRIO infusion set and the number of units which each filter could tolerate at these high flow rates was noted. Differences in the plasma haemoglobin content before and after filtration was measured to indicate erythrocyte damage. The results showed that in the fresher week-old blood all microfilters were more efficient in handling large volumes of blood and the haemolysis was less. Microfilters employing surface filtration methods were more efficient in the filtration of large blood volumes and caused less haemolysis than depth filtration microfilters.