Activated coagulation and activated partial thromboplastin times in assessment and reversal of heparin-induced anticoagulation for cardiopulmonary bypass.

In 22 adult patients, activated coagulation times (ACT) were compared to activated partial thromboplastin times (aPTT) before, during, and after cardiopulmonary (CP) bypass surgery. After intravenous heparin (150 units/kg), mean ACT increased from 131 +/- 14 (mean +/- SD) to 362 +/- 72 s (P less than 0.001). With 1.5 units of heparin/ml added to the priming solution of the pump, ACT ranged from 230 to 541 s and aPTT was always 300 s or longer. Activated PTT appears to be less sensitive to changing plasma heparin levels than ACT. Heparin neutralization with a protamine/heparin ratio of 1.0 returned ACT and aPTT to preheparin levels. No abnormal bleeding tendency was seen during the recovery period, and ACT and aPTT remained at preheparin levels. In 10 infants and children undergoing open-heart surgery, ACT was measured in response to the same heparin and protamine regimen. Baseline (113 +/- 14 s) and post-heparin (297 +/- 90 s) ACT were shorter in children than in adults (P less than 0.01). After protamine, ACT was still longer than baseline (134 v 113 s, P less than 0.05). Infants and children seem to require more heparin/kg body weight than adults to achieve comparable ACT levels.