Antithrombin Concentrates in Heparin-Resistant Cardiopulmonary Bypass Patients

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Abstract
Antithrombin, a serine protease inhibitor, plays an important role in the regulation of the coagula tion cascade. It inhibits thrombin as well as factors Xa, IXa, XIa, and XIIa. Heparin markedly accelerates the rate at which antithrombin inhibits these enzymes. To prevent the formation of clots in the extracorporeal cir cuit, heparin is used during cardiopulmonary bypass sur gery (CPB). However, in a small proportion of patients, adequate anticoagulation, defined as an activated clotting time (ACT) of >400 s after an intravenous bolus of hep arin in a dose of 300 U/kg, is not achieved. Conventional treatment of heparin resistance includes fresh frozen plasma or large doses of heparin. Antithrombin concen trates were given to 12 patients who were considered to be heparin resistant at our institution. All patients had received >300 U/kg of heparin before antithrombin con centrates were infused. In all patients, the ACT pro longed to >400 s after concentrates were infused, and in nine of 12 cases to >600 s. Of these nine patients, six (67%) did not receive any allogeneic transfusions, whereas three (33%) required allogeneic blood transfu sions. In nine of 12 patients, no more heparin was given after infusing antithrombin concentrate. It appears that antithrombin concentrate, which is a fractionated, pas teurized plasma product, is a possible safer alternative to excessive heparin doses or fresh frozen plasma for CPB patients who are heparin resistant. Key Words: An tithrombin—Cardiopulmonary bypass—Heparin resis tance.