Anticoagulation and thrombosis-
Considering the known Covid-19 associated thrombotic microangiopathy and early pro-thrombotic tendencies of the other Covid-19 patients, the normal low intensity heparin protocol was prophylactically increased to a moderate intensity heparin protocol (11). At our institution, an in-vivo therapeutic range of heparin (unfractionated anti-Xa range of 0.3 – 0.5 IU/mL) correlates with an aPTT range of 64 – 102 seconds. Given the bleeding and thrombotic complications in ECMO patients, a tighter range of 70 – 90 seconds was targeted post-cannulation. If a patient demonstrated a poor response to heparin, defined by as significant clot formation during cannulation, increasing fibrin deposition on the inlet or outlet of the oxygenator, frequent clotting within the CRRT circuit, or type 2 heparin induced thrombocytopenia (HIT) despite an aPTT within range, systemic anticoagulation was transitioned to bivalirudin with a goal aPTT of 75-95 seconds. Eleven patients were started on a heparin infusion post-cannulation while three patients were started on a bivalirudin infusion. Of the 11 patients initially on the heparin infusion, 8 were later transitioned to bivalirudin due to the reasons cited above. Additional details on the anticoagulation course are shown in Table 3. During the transition from heparin to bivalirudin, the bivalirudin was infused for 30 minutes prior to heparin discontinuation. Aspirin was administered on a case by case basis dependent upon clot formation within the circuit as well as in cases with evidence of an elevated maximum amplitude (MA) on the thromboelastograph (TEG). A transfusion policy was maintained for packed red blood cells, with administration for a hemoglobin < 8g/dL with evidence of inadequate oxygen delivery. Platelets were maintained >50,000/mm3 unless the patient was actively bleeding.