In 30 consecutive children with congenital heart disease scheduled for pediatric cardiac operations, thrombomodulin, protein C, free protein S, and thrombin-antithrombin complex were measured by enzyme-linked immunosorbent assay after the induction of anesthesia (baseline value), and then before, during, and after cardiopulmonary bypass until the first postoperative day. The patients were divided prospectively into two groups: children weighing less than 10 kg (group 1; n = 15) and those weighing more than 10 kg (group 2; n = 15). At baseline, the plasma concentration of thrombomodulin was significantly higher in the children in group 1 than in those in group 2 (83.1 +/- 11.0 ng/mL versus 29.2 +/- 12.1 ng/mL). During cardiopulmonary bypass, the thrombomodulin level was reduced in both groups without showing any significant group differences. Five hours after cardiopulmonary bypass and on the first postoperative day, the thrombomodulin level exceeded normal values only in the children weighing less than 10 kg. In both groups, the protein C levels were already below normal at the beginning of the study. The baseline protein S concentration was higher in the smaller children (80% +/- 18%) than in the larger children (66% +/- 11%). It was reduced by cardiopulmonary bypass in both groups; however, postoperatively it did not return to normal m group 1 (45.1% +/- 10%). Plasma levels of the thrombin-antithrombin complex were similar in both groups, with a marked increase at the end of cardiopulmonary bypass, and returned to near-normal levels by 5 hours after bypass. Other coagulation variables (the partial thromboplastin time and the antithrombin III and fibrinogen levels were not significantly different between the two groups. Postoperative blood loss was significantly higher in the smaller children on the first postoperative day (35.3 +/- 20.1 mL/kg) than in the children weighing more than 10 kg (11.8 +/- 5.0 mL/kg). Five children in group 1 and 2 children in group 2 received fresh frozen plasma in the postbypass period (p < 0.05). It is concluded that the endothelium is involved in the regulation of hemostasis by producing the natural anticoagulant thrombomodulin. This endothelium-related system was significantly more altered in the smaller children with congenital heart disease undergoing cardiac operations, than it was in the bigger children, which may have contributed to the greater bleeding tendency in these children.
