Can lean body mass be used to reduce the dose of heparin and protamine for obese patients undergoing cardiopulmonary bypass?

Increasing numbers of obese patients are presenting for cardiac surgery. The convention for heparin dose dictates that a bolus of 300 IU heparin per kilogram of total body weight (TBW) is administered before CPB. During CPB, the activated clotting time (ACT) is maintained for longer than 480 seconds. At the end of the procedure, protamine is administered to neutralize heparin and achieve hemostasis. Both of these drugs can have serious side effects: heparin can induce thrombocytopenia, and protamine has been known to cause reactions in patients allergic to fish, vasectomized men, and some patients with insulin-dependent diabetes. The calculation of lean body mass (LBM) may be a more accurate method of determining drug doses as opposed to TBW and may avoid giving obese patients a relative overdose of heparin, which must subsequently be neutralized with protamine. LBM can be determined by different methods. This study used bio-electrical impedance analysis as a simple, quick, and accurate method of calculating LBM. A comparison was made between two groups of patients whose body mass index (BMI) was >27 kg/m2: Group 1, n = 13, mean BMI = 32, mean body fat = 36% received the conventional dose of 300 IU/kg heparin for their TBW. Group 2, n = 14, mean BMI = 31, mean body fat = 35% received a dose of 300 IU/kg heparin for their calculated LBM. ACT was conducted before and after heparin administration. Additional heparin was administered as required to achieve target ACT > 400 s. Mean ACT results and total heparin doses were analyzed using unpaired two tailed t tests. Our results indicate that with care, a reduction of as much as 25% in the doses of heparin (p = 0.0001) and protamine can be achieved for a substantial number of patients classified as overweight or obese.