Kinetics and sites of sequestration of indium 111-labeled human platelets during cardiopulmonary bypass.

A new approach for the study of the kinetics and quantification of the in vivo and ex vivo sites of sequestration of platelets during cardiopulmonary bypass (CPB) is described. Autologous platelets of four patients were labeled with 111In-oxine and reinfused on the day prior to CPB for coronary artery bypass grafting. Changes in blood 111In-labeled platelet radioactivity and blood platelet counts were monitored during the operation. In vivo 111In-labeled platelet redistribution was quantified with a scintillation camera and a computer-assisted imaging system before and after CPB. Sequestration of 111In-labeled platelets in the bubble oxygenator was measured. 111In-labeled platelet activity in the blood decreased by 46% +/- 5% within 5 minutes of CPB, but this decrease was mostly due to hemodilution; the true loss of platelets from the circulation was 13% +/- 4%. Intraoperatively, whole body 111In activity decreased by oxygenator 10.8% +/- 1.3% of administered platelets were sequestered, especially in the innermost active layers of the defoaming mesh of the bubble oxygenator. Mean survival time of circulating platelets was 58 +/- 8 hours and fitted an exponential function best. The bleeding time increased to 40 minutes during operation and returned to normal within 24 hours. During operation 111In-labeled platelets accumulated somewhat in the liver (10.7%) but not in the spleen, thorax, or head. In the 48 hours after operation, platelets were sequestered mainly in the liver. The scintillation camera with computer-assisted imaging allows in vivo quantitative studies of platelet kinetics of a type which has not been possible with previous techniques.