Protamine Requirements in Cardiac Surgery: Effect of Changes in the Heparin Reference Standard

OBJECTIVE: UFH (unfractionated heparin) and protamine are integral to cardiac surgery, and inappropriate dosing can predispose to coagulopathy and hemorrhage. The FDA (Food and Drug Administration) recently has instituted changes to UFH formulation and it is not known if this has influenced its susceptibility to neutralization by protamine. Hence, the authors sought to compare 2 commercial preparations of UFH (old and new) with regard to their neutralization by protamine in patients undergoing cardiopulmonary bypass (CPB). DESIGN: Prospective, observational, cohort study. SETTING: Tertiary care university hospital and associated research laboratory PARTICIPANTS: Twenty adult patients undergoing elective cardiac surgery with CPB. INTERVENTIONS: Blood samples were drawn preinduction, prior to, and 5 and 30 minutes following protamine, and 0 and 2 hours after ICU admission. Protamine titration assays were conducted in vitro on samples drawn prior to and following protamine administration. Anti-IIa and anti-Xa activity were assayed in all samples. RESULTS: Anti-IIa and anti-Xa activity were detected ubiquitously at all time points following CPB, and there were no differences in susceptibility to protamine neutralization between the 2 groups. In vitro protamine titration studies revealed that anti-IIa was more resistant to protamine neutralization compared to anti-Xa activity. CONCLUSIONS: The 'old' and 'new' formulations of UFH evaluated in this study were similar in their susceptibility to protamine neutralization. Circulating UFH is detected as early as 5 minutes after protamine administration and anti-IIa is more resistant to protamine neutralization as compared to anti-Xa activity. Further studies are required to quantify the precise dose of protamine following CPB.