Antithrombin III (AT) is a protease that disrupts coagulation by inactivating thrombin. Congenital AT deficiency can be a quantitative and/or qualitative issue. Fortunately, AT concentrates like Thrombate III (pooled from human plasma) can replenish deficits.
As a cardiothoracic anesthesiologist, I routinely administer large amounts of heparin to potentiate AT activity. The goal is to create enough systemic anticoagulation to safely initiate cardiopulmonary bypass.
If patients have a suboptimal response to standard doses of heparin as determined by an activated clotting time (ACT), I’ll typically bolus more heparin (up to 600 units/kg total); however, if there’s AT deficiency at play, heparin’s dose-response curve is affected leading to resistance. At this point, I have two choices to restore antithrombin III: transfuse fresh frozen plasma (FFP) since this contains AT or administer an AT concentrate like Thrombate III.
Although Thrombate III is more expensive than FFP, it requires less volume administration and carries a lower risk of infection and transfusion-related acute lung injury (TRALI).
Drop me a comment below with your experience regarding AT!