Is Activated Clotting Time an Accurate Measure of Heparinization for Neonates Receiving ECMO? † 999

Introduction: In most ECMO centers, activated clotting time (ACT) is obtained at the bedside during neonatal ECMO and used to titrate heparin infusion. We hypothesized that ACT would not correlate with heparin infusion rate or heparin level in neonatal ECMO patients. In addition, we hypothesized that there would be fewer clots in the ECMO circuit if we infused heparin at a minimum rate of 25 units/kg/hour, compared to titrating the heparin infusion rate based on the ACT alone. Methods: From April 1996 through August 1997, all patients on ECMO were monitored with hourly ACT and daily chromagenic Xa heparin assay. The ACT and heparin assay were done simultaneously. We performed a regression analysis to determine if ACT correlated with heparin level or heparin infusion rate and if heparin level correlated with heparin infusion rate. We also performed a retrospective chart review of 70 patients requiring ECMO from October 1992 to September 1997 to determine the presence of clots in the circuit throughout the ECMO run. We changed our policy to maintain the heparin infusion at a minimum of 25 units/kg/hour in April 1997. We then compared the incidence of clots in the ECMO circuit before and after initiation of the minimum heparin infusion. Results: A total of 69 heparin assays were done simultaneously with ACTs on 13 patients. See table. Sixty patients were managed by titrating heparin in response to the ACT alone. Ten patients were managed by titrating heparin infusion using the ACT but not decreasing the infusion rate below 25 units/kg/hour. 77.1%of all patients on ECMO had clots in their circuit. Significantly more patients managed with ACT alone had clots (82%) than patients managed with a minimal heparin infusion rate of 25 units/kg/hr (50%; p < 0.05 by Chi square). Conclusion: In this group of patients, ACT did not correlate with either heparin assay or heparin infusion rate. Heparin assay did correlate with heparin infusion rate. Patients maintained on a heparin infusion of at least 25 units/kg/hr had a lower incidence of clots in the ECMO circuit. We conclude that ACT by itself is not an accurate measure of heparinization for neonates receiving ECMO.

Table 1 No caption available.