Heparin and antithrombin III levels during cardiopulmonary bypass: correlation with subclinical plasma coagulation.

The anticoagulant effect of heparin in the milieu of altered antithrombin III levels was investigated in adult (n = 7) and pediatric (n = 14) patients undergoing open heart operations. The pediatric patients were subdivided into a control group (n = 8) and an antithrombin III group (n = 6), which received 1,000 units of antithrombin III. The reduction in antithrombin III levels during cardiopulmonary bypass was obvious in patients of all ages, showing a greater reduction (although not statistically significant) in the pediatric patients. However, the antithrombin III group patients maintained their preoperative levels of antithrombin III. The elevated fibrinopeptide A levels in pediatric and adult control group patients suggested that considerable subclinical plasma coagulation occurred during open heart operations, especially during the normothermic period of cardiopulmonary bypass and after the administration of protamine. Antithrombin III levels in the children were the most predictive (r = -0.58; p < 0.001) for production of fibrinopeptide A during moderate hypothermic cardiopulmonary bypass, but the heparin levels were most predictive (r = -0.57, p < 0.03) in the adults. This result may be related to the different actions of heparin when antithrombin III levels are reduced. Supplementation with antithrombin III succeeded in suppressing the activation of the coagulation cascade and resulted in no statistical change in fibrinopeptide A levels at any time. We conclude that heparin and (in some patients) antithrombin III levels are important variables for the inhibition of fibrin formation and the possible preservation of coagulation proteins.