Optimal Heparin Dosing Regimens for Cardiopulmonary Bypass

300u/kg of heparin for CPB ACT performed. If ACT is \< 480 seconds a bolus of 5000u heparin will be given. ACT will be repeated and bolus given until ACT is\>480 seconds

initial dose of 450u/kg for CPB ACT performed additional bolus given if result is \<600 seconds anytime during CPB

will have anticoagulation during CPB assessed with heparin concentration monitoring and heparin dose response (HDR) to determine the optimal dosage of heparin. This group will evaluate the possible benefit of the HDR to determine heparin dosing and monitoring to achieve maximal suppression of thrombin compared to a fixed dose of heparin as the other two groups. Additional heparin doses will be given to maintain a specific heparin concentration according to the HDR. This is a recognized way of managing heparin dosing and anticoagulation for CPB. All three groups will have heparin neutralized by protamine. Adequacy of heparin neutralization will be based on a difference between the ACT and heparinase-treated ACT values of less than 10%