Whole blood heparin concentrations do not correlate with plasma antifactorXa heparin concentrations in pediatric patients undergoing cardiopulmonarybypass

This study was designed to test the validity of whole blood heparin concent ration (WHBC) measurements using an on-site protamine titration assay with the Hepcon instrument (Medtronic Blood Management, Parker, CO, USA) in pedi atric patients less than 1 year old undergoing cardiopulmonary bypass (CPB) . The validity of the Hepcon measurements was examined via a test of correl ation with the gold standard plasma antifactor Xa activity (anti-Xa) assay. Fifty-one patients (23 females and 28 males) under 1 year old (mean age 5. 3 months) were studied prospectively. Blood samples were taken at 5 min int o CPB and at the end of CPB for the WBHC, plasma anti-Xa activity, and hema tocrit (Hct). The WBHC was converted to plasma heparin level using a formul a taking into account the collection of blood into citrate solution and the effect of the citrate on the hematocrit. While a nonparametric statistical analysis revealed that the mean corrected values from the Hepcon instrument were not significantly different from th e mean anti-Xa values (p = 0.070 at 5 min on CPB, p = 0.518 at the end of C PB), there was no significant correlation between these values at either 5 min into CPB (r = 0.123, p = 0.429) or at the end of CPB (r = -0.247, p = 0 .080). The lack of correlation between the two assays may be related to the extreme hemodilution observed during CPB in small children, which leads to very low concentrations of coagulation proteins. Due to this discrepancy, whole blood heparin monitors should be further evaluated in children underg oing CPB.