[Heparin dosage in long-term intravenous administration based on the example of vascular surgery patients]

For prophylaxis of deep-vein thrombosis, 23 male and 7 female patients received intravenous 15 000 IE/24 h sodium-heparin continuously after different operations for blood-vessel surgery. The plasma heparin concentration was measured with chromogenic substrate at 0, 1, 2, 4, 8 and 12-18 hours after beginning of heparin application. Each patient's hematocrit, sex, height, weight and parameters of liver and renal function were measured at the same time. The aim of this investigation was to find a general model for intravenous heparin application which would allow the best individual therapeutic plasma heparin concentration to be obtained. At the latest eight hours after the beginning of heparin-infusion the steady state of plasma heparin concentration was reached in 100%, but only in 56.67% it equalled the therapeutical factor Xa inhibition-level of 0.10 IE/ml to 0.20 IE/ml (= 0.077 USP-E/ml to 0.154 USP-E/ml). It was found that the plasma heparin concentration correlates negatively with the plasma volume. The heparin halftime depends on the dosage. Plasma heparin concentrations from 0.04 IE/ml to 0.20 IE/ml (= 0.031 USP-E/ml to 0.154 USP-E/ml) correlate to heparin halftimes of 9 min to 38 min. With this results formulae for calculating the quantity of the bolus and the daily heparin application were obtained. As opposed to the liver function the kidney function does not have any significant effect on the plasma concentration of biological active heparin. Furthermore it was found that the actual weight is unreliable for determination of the dosage. Instead calculated weight (height minus 100) is to be used.