Extracorporeal Membrane Oxygenation (ECMO)

What is ECMO?

• An inflow cannula draining blood from the patient
• A centrifugal pump maintaining flow
• A membrane oxygenator (adds O2, removes CO2)
• An outflow cannula returning blood to the patient

Types of ECMO

1. Venovenous (VV) ECMO - Respiratory support only

• Drains deoxygenated blood from a large vein (femoral or IJ), oxygenates it, and returns it to a central vein (typically IJ or femoral)
• Provides lung support only - the native heart still handles circulation
• Used for severe, refractory respiratory failure

2. Venoarterial (VA) ECMO - Cardiac + respiratory support

• Drains from a vein (femoral or IJ) and returns oxygenated blood to an artery (femoral or subclavian graft)
• Provides both cardiac and pulmonary support
• Used in cardiogenic shock, cardiac arrest, biventricular failure

3. Hybrid configurations

• V-AV (veno-arteriovenous), VV-A, and other variations exist for complex cases
• A decision algorithm based on the degree of hypercarbia/hypoxemia and cardiac function guides cannulation type selection

Indications

VV ECMO (Respiratory)

• Severe ARDS (viral or bacterial pneumonia, aspiration, any cause)
• Status asthmaticus
• Pulmonary contusion
• Inhalation injury
• Severe air leak syndrome
• Airway obstruction (e.g., mediastinal mass)
• Pre- and post-lung transplant

VA ECMO (Cardiogenic)

• Refractory cardiogenic shock (any cause)
• Failure to separate from cardiopulmonary bypass
• Bi-ventricular failure
• Cardiac arrest without return of spontaneous circulation
• Massive pulmonary embolus
• Refractory unstable arrhythmias
• Anaphylaxis
• Bridge to durable VAD or transplant

Contraindications

VV ECMO

• Injurious mechanical ventilation for ≥7 days
• Major pharmacologic immunosuppression
• Recent or expanding intracranial hemorrhage
• BMI >40-45 (technical/flow difficulties)
• Neither recovery nor lung transplant candidacy is plausible

VA ECMO

• Acute intracranial hemorrhage or massive stroke
• Active bleeding
• Severe aortic insufficiency

• Contraindication to anticoagulation
• Active cancer, end-stage liver disease
• Advanced age, morbid obesity
• Aortic dissection, chronic hemodialysis

ECMO as Bridge Therapy

Key Complications

Bleeding

• Most common significant complication
• Caused by required anticoagulation, thrombocytopenia, mechanical platelet destruction, and clotting factor loss
• Common sites: epistaxis, GI; rare: intracranial, pulmonary

Thrombosis / Anticoagulation management

• Unfractionated heparin is standard (monitored via PTT or activated clotting time)
• Bivalirudin or argatroban used if heparin-induced thrombocytopenia (HIT) is a concern; no reversal agent available for these
• Contact with circuit surfaces activates coagulation cascade (vWF binding, thrombin formation, cytokine storm in severe cases)

VA ECMO-specific

• Pulmonary edema and LV fluid overload - because VA ECMO supports circulation but doesn't unload the LV; may need IABP, Impella, or inotropes for LV unloading
• Harlequin (differential hypoxia) syndrome in femoral VA ECMO

Cannulation-related

• Limb ischemia (distal perfusion catheter often placed in femoral artery cases)
• DVT, vessel injury - mitigated with ultrasound-guided cannulation

Key Clinical Trials

CESAR Trial

• Patients with severe ARDS transferred to ECMO center vs. conventional management
• ECMO group: 37% mortality at 6 months vs. 53% in conventional group
• Supported development of ECMO centers of clinical excellence

EOLIA Trial (2018)

• 248 patients with severe ARDS randomized to VV ECMO vs. conventional ventilation
• Inclusion: P/F ratio <50 for >3h or <80 for >6h, pH ≤7.2, MV <7 days
• No statistically significant mortality difference (35% ECMO vs. 46% control at 60 days)
• However: 35/125 control patients crossed over to ECMO (higher mortality in crossover group); ECMO group had fewer treatment failures, less renal replacement, less prone positioning
• Trial stopped early for futility, but criticized for underpowering and high crossover rate

H1N1 Pandemic Experience (2009)

• VV ECMO in severe viral pneumonia/ARDS: survival rate 78% in a multicenter series (average P/F ratio 56)
• Major inflection point in global VV ECMO adoption

Special Considerations