This study will evaluate heparin as compared to bivalirudin for systemic anticoagulation in adult patients that require extracorporeal membrane oxygenation (ECMO). Half of the participants will receive heparin and half will receive bivalirudin.

The investigators will randomly assign 34 adult patients requiring ECMO to receive bivalirudin or unfractionated heparin in a 1:1 fashion. There will be 17 patients in each group for a total of 34 patients.

Unfractionated heparin binds to antithrombin thereby causing an anticoagulant effect while bivalirudin binds directly to thrombin. Use of unfractionated heparin in this population is problematic due to reliance on adequate levels of circulating antithrombin, complex pharmacokinetics, and variable clearance. Bivalirudin avoids many of these difficulties.

Inclusion Criteria:

1. Age ≥18 years
2. Require ECMO and systemic anticoagulation as determined by the primary treating physician
3. Require anticoagulation to target an activated partial thromboplastin time (aPTT) of 40-60 seconds or 60-80 seconds

Exclusion Criteria:

1. Prior inclusion in this study
2. Patients with known or suspected heparin induced thrombocytopenia
3. Systemic anticoagulation at Legacy for ≥ 24 hours during ECMO immediately prior to study enrollment
4. Allergy to heparin or related products or bivalirudin
5. Known anti-thrombin deficiency
6. Selection of a non-standard aPTT target range