Intravascular platelet aggregation and spontaneous contrast.

The purpose of this study was to determine why spontaneous contrast developed after general anesthesia in dogs. Twenty-seven dogs underwent echocardiography before and after pentobarbital or chloralose-urethane general anesthesia. The results showed that none of the 12 dogs receiving pentobarbital and 10 of 15 dogs receiving chloralose-urethane anesthesia developed contrast, in association with large platelet and platelet-neutrophil aggregates (P < 0.01); this effect could also be reproduced in vitro. The administration of adenosine diphosphate or antiplatelet antibody to nine dogs confirmed that intravascular platelet aggregation can cause ultrasonic contrast. The implications of these findings for patients with spontaneous contrast are discussed.