Cardiopulmonary bypass surgery. Platelet aggregation during induction of anesthesia and following heparinization of patients.

Measurements of platelet count and platelet aggregation in response to adenosine diphosphate and epinephrine were made before and after administration of preanesthetic medications and at intervals during induction of anesthesia, before and after thoractomy, and before and after systemic heparinization in patients undergoing cardiopulmonary bypass operations. Substantial decreases in circulating platelet count occurred only after induction of anesthesia and following thoracotomy. There was no notable change in the percent of platelets involved in aggregation over the period studied, but the reactivity of platelets was increased after induction of anesthesia and after thoracotomy.