PLATELETS IN SHED MEDIASTINAL BLOOD USED FOR POSTOPERATIVE AUTOTRANSFUSION

Ten patients undergoing open-heart surgery received postoperative auto transfusion of shed mediastinal blood collected in the cardiotomy rese rvoir. The number, function and morphology of the platelets found in t he shed blood were investigated. Platelets were counted using an elect ronic counter compared with light microscopy. Morphology of platelets was studied with electron microscopy. Platelet aggregation was studied using an aggregometer. Dense granule secretion was measured as the ex tracellular appearance of adenosine triphosphate. Enumeration of plate lets in shed blood using the two methods gave different results. Thus, the electronic counter gave a mean platelet count of 62 . 10(9) . l-1 , while light microscopy revealed only a mean platelet count of 10 . 1 0(9) . l-1. Electron microscopy disclosed few platelets, but numerous cytoplasmatic fragments smaller than or up to the same size as platele ts. The platelets found were mostly shape-changed, spheroid, character ized by centralization and loss of alpha-granules and dense bodies, al l changes that indicated irreversible platelet activation. The platele ts failed to aggregate in response to the presence of thrombin, adenos ine diphosphate or collagen, and secretion of adenosine triphosphate w as absent. Plasma from the shed blood was not capable of inducing spon taneous aggregation in platelet-rich plasma from healthy donors. These results indicate that infusion of larger volumes of autotransfused bl ood should be supplemented with platelet concentrates.