DIFFERENT ANTICOAGULANTS AND PLATELET REACTIVITY IN CARDIAC SURGICAL PATIENTS

A technique for assessing platelet reactivity to shear stress from non anticoagulated blood samples was employed to compare the relative effe cts of an unfractionated heparin, a low-molecular-weight heparin, and hirudin. The in vitro platelet effect of unfractionated heparin (5 U/m L) was measured in 290, the effect of a low-molecular-weight heparin ( 1 anti-Xa unit/mL) in 74, and the effect of hirudin (8 mug/mL) in 50 c ardiac surgical patients. The relative proportions of patients exhibit ing an enhanced platelet reactivity, a mild to moderate inhibition, an d a severe inhibition were, respectively: 8.6%, 58.6%, and 32.8% for u nfractionated heparin; 22%, 66%, and 12% for the low-molecular-weight heparin; and 6%, 66%, and 28% for hirudin. At the concentrations exami ned, a significantly greater proportion (p < 0.01) of the patients exh ibited enhanced platelet reactivity and a significantly smaller propor tion (p < 0.01) showed severely inhibited platelet reactivity associat ed with the low-molecular-weight heparin versus the unfractionated hep arin, whereas there was no significant difference between the patients treated with hirudin and unfractionated heparin. Although the relevan ce of this study is limited because the clinically appropriate concent ration of the alternative anticoagulants and comparative doses are unk nown, it can be inferred that low-molecular-weight heparin may reduce the blood loss associated with cardiopulmonary bypass.