Anticoagulation is necessary for most pediatric and adult extracorporeal membrane oxygenation (ECMO) patients to prevent circuit clotting. Inherently, the most common side effect of anticoagulation is bleeding. Anticoagulation during ECMO is complex due to patient critical illness, interactions between the patient and ECMO circuit, and the inflammatory responses of the patient to illness and to the ECMO circuit which all lead to imbalance in normal patient hemostasis.