Loss of platelet fibrinogen receptors during clinical cardiopulmonary bypass

In 10 patients, cardiopulmonary bypass decreased the number of fibrinogen binding sites from 31,730 ± 12,802 per platelet to 18,590 ± 9,644 per platelet. Bypass also decreased the amount of the platelet membrane glycoprotein IIIa, which is part of the fibrinogen receptor complex, from 17.1 ± 3.6 ng/109 platelets to 12.9 ± 4.7. The fibrinogen binding constant did not change. Platelet sensitivity to adenosine diphosphate did not change; however, template bleeding times increased from 5.2 ± 1.5 minutes before bypass to 8.5 ± 2.3 minutes after bypass. Analysis of detergent washings from the perfusion circuit after bypass in five patients indicated that platelet material remains attached to the surface as membrane fragments and degranulated platelets. These data further elucidate the mechanism of platelet loss and dysfunction during cardiopulmonary bypass and highlight the importance of platelet membrane fibrinogen receptors and surface adsorbed fibrinogen in this process.