Summary of Risks and Benefits: ATryn® is FDA approved for use in the prevention of peri-operative and peri-partum thromboembolic events in hereditary antithrombin III deficient patients. ATryn® is a transgenically produced recombinant antithrombin concentrate from goat milk that is preservative free. It has an identical amino acid structure with minor glycosylation differences to endogenous human AT IIII. When assayed in the presence of excess heparin, the potency and efficacy of ATryn® is not different from that of plasma-derived AT III concentrates.5 ATryn® is administered as a continuous intravenous infusion, with weight-adjusted loading and maintenance dosing regimens as recommended by the medication's package insert. As dosing is specific to a patient's weight, this theoretically minimizes the risk for overdosing. In addition, as dosing is administered as a continuous infusion that is titrated to maintain stable AT III levels, there is the additional potential for less fluctuations in a patient's AT III levels. Not only will anticoagulation be optimized throughout the duration of ECMO support, but theoretically there may be a decreased need for, or less fluctuations in a patient's heparin requirements. This may furthermore minimize the risk for thromboembolic events within the ECMO circuit and the patient. Additionally, ATryn® is preservative free and because it is a recombinant product, it should be free from the risk of viral infection or prion transmission.