[Factor Xa inhibitory assay to detect plasma heparin concentrations during and after cardiopulmonary bypass].

OBJECTIVE: For establishment and application of Xa Factor Inhibitory Assay to detect plasma heparin concentrations during and after cardiopulmonary bypass (CPB) and to evaluate the treatment with low-dose protamine reversal of heparin. METHODS: Venous blood samples were drawn from 25 patients with rheumatic valvular disease undergoing valvular replacement at different points (before CPB, after 5 min of heparinization, at termination of CPB, after 10 min, 1 hr and 5 hr of protamine reversal of heparin), and the plasma heparin concentrations were detected. RESULTS: The mean of plasma heparin concentration was the highest (13.16 U/ml) after 5 min of heparinization. At termination of CPB, it decreased (11.06 U/ml) and was significantly different from the concentrations at other points (P < 0.05). After 10 min of low-dose protamine reversal of heparin, the heparin concentration (0.45 U/ml) decreased to the same as that before CPB and continued to be stable at 1 hr and 5 hr; there was no significant difference in heparin concentration between these 4 points (P > 0.05). The highest batch CV in standard curves was 11.65%; the lowest was 0.37%. CONCLUSION: Factor Xa Inhibitory Assay is of good accuracy and repetition. The results from its clinical application demonstrated that the plasma heparin concentration of the patient at termination of CPB should be used for reference in determining the dose level of protamine for that every patient subjected to CPB.