Improved methods for estimating initial heparin infusion rates.
Two methods of calculating heparin infusion rates for patients with venous thrombotic disease were compared; one method was based on a one-compartment pharmacokinetic model, the other on patient weight. Sixty-eight patients with presumed thromboembolic disease were started on continuous i.v. heparin sodium (porcine) using an infusion pump. Patients were divided into two groups--the infusion rate of Group I was based on patient weight (77 units/kg/4 hrs) and the infusion rate of Group 2 was determined by a pharmacokinetic equation based on a one-compartment heparin model. Heparin effect was measured by an activated partial thromboplastin time (APTT). The initial heparin infusion rate for Group 1 (4,784 +/- 672 units/4 hrs) was significantly greater (p less than 0.039, two-sample t-test) than that for Group 2 (4,413 +/- 779 units/4 hrs), but the variances of the rates were not significantly different (p = 0.40, ratio of variance F-test). Both methods for estimating initial heparin infusion rates gave mean APTT values in the center of the therapeutic range, but the variance in the APTTs of Group 2 patients was significantly smaller (p = 0.004) than that of Group 1. The pharmacokinetic model was more precise and reliable. This model should be valuable for insuring heparin's therapeutic effect without exposing patients to the potential risk of hemorrhage.