Post-thaw suspension of red cells cryopreserved with hydroxyethyl starch.

Post-thaw testing of large units of red cells frozen with 14% hydroxyethyl starch (HES) indicates 97-98s of the cells are recovered and about 85% are stable in saline (1). The quantity of supernatant hemoglobin present in such units at thaw is generally near 450-550 mgs. We have been unable to obtain consistent results which reveal a substantial improvement over these values, This quantity of free hemoglobin at thaw ,and the increased level of extracellular potassium discourage administration of these units without postthaw processing. Because further empirical manipulation of freezing and thawing conditions has proved unrewarding, we examined the feasibility of a simple post-thaw wash. The wash was considered mainly a dilution which, when followed by centrifugation, could permit direct administration of units, Such a wash would remove most free hemoglobin and extracellular potassium and would reduce the viscosity of the HES-red cell mixture. Since HES is not physiologically damaging on transfusion it would not be necessary to remove all of the cryoprotectant. We noted that during postahaw washing the level of supernatant hemoglobin in the