Variation in platelet size during recovery from thrombocytopenia following extracorporeal circulation.

Serial platelet counts and measurements of mean platelet volume have been performed on patients who became thrombocytopenic during open heart surgery. The results show that large platelets are released from the bone marrow during the 48 hours following the operation as a primary response to an acute increase in demand. During this period there is only a gradual recovery of the platelet count. In the subsequent days there is an acceleration of platelet production and a simultaneous reduction in platelet volume. These results suggest a change in the nature of the stimulus following the initial postoperative period, indicating a close relationship between platelet size and the total platelet count. Platelet size, therefore, may not be wholly dependent upon either megakaryocytic heterogeneity or platelet age.