BACKGROUND: A study in humans showed that the transfusion of previously frozen human platelets after cardiopulmonary bypass, despite decreased survival, resulted in better hemostatic function than that of liquid-preserved platelets stored at 22 degrees C for 3 to 4 days. STUDY DESIGN AND METHODS: In this study, fresh, 3- to 4-day-old liquid-preserved, and cryopreserved human platelets were studied by the use of monoclonal antibodies directed against p-selectin, glycoprotein (GP)Ib, activated GPIIb/IIIa, and coagulation factor V in a three-color flow cytometric method. RESULTS: The fresh and liquid-preserved platelets had normal surface levels of GPIb, while the cryopreserved platelets were composed of distinct subpopulations of GPIb-normal and GPIb-reduced platelets. On the basis of the binding of factor V, both subpopulations of cryopreserved platelets exhibited greater surface binding of factor V than did fresh and liquid-preserved platelets. Activated GPIIb/IIIa was elevated on GPIb-normal platelets, but not on GPIb-reduced platelets. Baboon platelets frozen by a procedure identical to that used to freeze human platelets also had GPIb-normal and GPIb-reduced subpopulations after the freezing-thawing-washing procedure. Autologous cryopreserved baboon platelets labeled with biotin-X-N-hydroxysuccinimide showed a rapid removal of GPIb-reduced platelets during the 5-minute postinfusion period, whereas GPIb-normal platelets had an in vivo recovery of 48 percent and a lifespan of slightly less than 6 days. CONCLUSIONS: Improved in vivo function of cryopreserved platelets may be related to the rapid hemostatic effect of the GPIb-reduced subpopulation secondary to increased binding of factor V and expression of p-selectin.

Patients undergoing hypothermic cardiopulmonary bypass are often receiving aspirin therapy. Hypothermia, aspirin and cardiopulmonary bypass can each induce a platelet function defect, but it is not known if the effects of aspirin and hypothermia are additive in this regard. To address this question in humans in vivo, the forearm skin temperature of healthy volunteers was equilibrated and maintained at either normothermia (32 degrees C) or hypothermia (28 degrees C or 22 degrees C) before and 16 h after the ingestion of 650 mg aspirin. A standardized template bleeding time was performed on the forearm and the shed blood emerging from the wound was assayed for platelet surface P-selectin expression by whole blood flow cytometry (reflecting alpha granule secretion) and thromboxane B2 (the stable metabolite of thromboxane A2) by radioimmunoassay. Hypothermia resulted in marked prolongation of the bleeding time. Aspirin resulted in prolongation of the bleeding time under normothermic conditions, but only minimally augmented the hypothermia-induced prolongation of the bleeding time. Platelet surface P-selectin up-regulation in shed blood was abolished by hypothermia. Aspirin had no effect on maximal platelet surface P-selectin expression under normothermic or hypothermic conditions. Both hypothermia and aspirin resulted in markedly reduced shed blood thromboxane B2. Although aspirin slightly augmented the hypothermia-induced reduction in shed blood thromboxane B2, the concentration of thromboxane generated in shed blood under hypothermic conditions in the absence of aspirin had no effect on platelet surface P-selectin or platelet aggregation in whole blood. In conclusion, as determined by three independent parameters of the shed blood emerging from a standardized bleeding time wound (bleeding time, platelet surface P-selectin, and thromboxane B2), aspirin did not significantly augment hypothermia-induced platelet dysfunction in vivo.

OBJECTIVE: The aim of the study was to compare the clinical effects and hemostatic efficiency of transfusions of platelets preserved in the frozen state for as long as 2 years with transfusions of platelets preserved in the conventional manner for as long as 5 days in patients undergoing cardiopulmonary bypass. METHODS: Seventy-three patients were prospectively randomly assigned to receive transfusions of cryopreserved or liquid-preserved platelets. Nonsurgical blood loss was measured during and after the operation. Bleeding time, hematologic variables, and the bleeding time site shed blood were assayed before cardiopulmonary bypass and at 30 minutes and 2, 4, and 24 hours after transfusion. In vitro platelet function tests were conducted on platelets obtained from healthy volunteers. RESULTS: No adverse sequelae of the transfusions were observed. Blood loss and the need for postoperative blood product transfusions were lower in the group receiving cryopreserved platelets. Lower posttransfusion platelet increments and a tendency toward decreased platelet survival were observed in patients receiving cryopreserved platelets. Hematocrit and plasma fibrinogen were significantly higher in this group, and the duration of intubation was shorter. In vitro, cryopreserved platelets demonstrated less aggregation, lower pH, and decreased response to hypotonic stress but generated more procoagulant activity and thromboxane. CONCLUSIONS: (1) Cryopreserved platelet transfusions are superior to liquid-preserved platelets in reducing blood loss and the need for blood product transfusions after cardiopulmonary bypass. (2) The reduction in blood loss in the patients receiving cryopreserved platelet transfusions after cardiopulmonary bypass probably reflects improved in vivo hemostatic function of cryopreserved platelets. (3) Some in vitro measures of platelet quality (aggregation, pH, hypotonic stress) may not reflect in vivo quality of platelet transfusions after cardiopulmonary bypass, whereas other in vitro measures (platelet procoagulant activity and thromboxane) do.