[Blood microfiltration. Scanning electron microscopic study of the aggregates retained by a transfusion filter made of polyurethane foam].

Preliminary studies of the transfusion filter Bentley PF 127, a polyfilter type with a graded serie of diameters of microfenestration are reported. Dog blood has been used in all instances of the trial phase. Variations of the hematological factors as well as biochemical disparities have been examined and all deposits were assessed by means of scanning electron microscope. Amounts of deposits increased with the blood age. As far as banked dog blood develops less microaggregates during storage than human blood, the SEM pictures reported are a plea for banked blood microfiltration in any transfusion to human beings. The deposits which were trapped in the polyurethane foam, had previously passed through a screen filter with pore size slightly wider than the standard one (250 microns instead of 170 microns). Unfortunately the possibility of thrombus formation is serious as far as banked blood is rather fragile, and due to a slow flow rate, the time of blood contact with the filter is enough to allow thrombus development. However, the amounts of clots greatly increased with the age of the blood. The importance of filtration by adsorption was not very visible. The future of such a depth filter is questionable: should we prefer a transfusion screen filter with small pore size, the efficiently of which is determined by its pore size, and which traps the microaggregates by mechanical retention, or a depth filter which is supposed to retain the microaggregates regard less of the size but which could be very easily thrombus invaded and does not allow a suffisant blood flow rate for patients needing large amounts of blood in period of initial resuscitation? The debate is open but we should recognize that a screen filter with small pore size is widely used in the hospitals.