Extracorporeal Membrane Oxygenation (ECMO)

What Is ECMO?

The ECMO Circuit

Two Main Types

1. Veno-Venous (VV) ECMO

• Support provided: Lungs only (oxygenation + CO₂ removal)
• Circuit: Blood drained from a large vein → oxygenated → returned to another vein (typically right heart)
• Common cannulation: Right femoral vein (inflow) + right internal jugular vein (outflow)
• Alternative: Dual-lumen single cannula (e.g., Avalon cannula) via right IJ
• Native cardiac function: Must be intact - VV ECMO does not provide hemodynamic support
• Primary use: ARDS, severe pneumonia, acute respiratory failure

2. Veno-Arterial (VA) ECMO

• Support provided: Heart AND lungs (full cardiopulmonary bypass equivalent)
• Circuit: Venous blood drained (femoral/IJ vein) → oxygenated → returned to an artery (usually femoral, less often subclavian via graft)
• Native cardiac function: Bypassed; provides systemic perfusion
• Primary use: Cardiogenic shock, cardiac arrest, bi-ventricular failure, post-cardiotomy shock
• Key limitation: Can cause pulmonary edema and left ventricular (LV) fluid overload; does not adequately unload a severely impaired LV. Often requires adjuncts like Impella, IABP, or inotropes to vent the LV.

Indications

Respiratory (VV ECMO)

• Severe ARDS (P/F ratio < 80 mmHg despite optimal ventilation)
• Acute respiratory failure refractory to conventional management
• COVID-19 associated severe ARDS
• Bridge to lung transplant
• Status asthmaticus / massive pulmonary embolism (selected cases)

Cardiac (VA ECMO)

• Cardiogenic shock (including MI-related)
• Cardiac arrest refractory to CPR (ECPR - extracorporeal CPR)
• Acute myocarditis
• Post-cardiotomy shock (failure to wean from bypass)
• Bridge to ventricular assist device (VAD) or heart transplant
• Drug-induced cardiovascular collapse (e.g., overdose)

Contraindications

• Absolute: Irreversible end-organ failure without transplant candidacy; severe aortic regurgitation (VA ECMO); aortic dissection
• Relative: Severe coagulopathy or uncontrolled bleeding; advanced age with poor prognosis; prolonged cardiac arrest without CPR (poor neurological prognosis)

Clinical Management on ECMO

• Anticoagulation: Unfractionated heparin (UFH) is standard; target anti-Xa or aPTT per institutional protocol. Heparin-induced thrombocytopenia (HIT) requires switching to argatroban or bivalirudin.
• Ventilator settings: "Lung rest" strategy on VV ECMO - low tidal volumes (2-4 mL/kg), low PEEP, low FiO₂ to prevent ventilator-induced lung injury (VILI)
• Flow rates: Typically 3-6 L/min in adults; adjusted based on patient weight and oxygenation needs
• Sweep gas: Controls CO₂ removal (higher sweep = more CO₂ removed)
• FiO₂ on circuit: Controls oxygenation
• Prone positioning: Can still be performed safely on VV ECMO

Key Complications

ECMO as Bridge Therapy

1. Bridge to recovery - heart/lungs heal; ECMO removed
2. Bridge to transplant - lung or heart transplant
3. Bridge to decision - time to assess neurological/organ recovery
4. Bridge to durable device - VAD implantation

Key Clinical Trials

• CESAR trial (2009): VV ECMO at specialized centers improved 6-month survival without severe disability vs. conventional ventilation in severe ARDS (63% vs 47%)
• EOLIA trial (2018): Randomized trial of VV ECMO in severe ARDS; did not reach its primary endpoint (mortality reduction at 60 days) due to high crossover (28% of control patients received ECMO). A Bayesian reanalysis by Golgher et al. suggested the trial was statistically underpowered and favored ECMO.
• Recent evidence (2026): A systematic review on long-term psychological outcomes after ECMO highlights significant PTSD, anxiety, and depression in survivors - an increasingly recognized area of post-ECMO care (PMID 42235101). For cardiogenic shock, a Lancet meta-analysis (2024) of individual patient data from randomized trials of temporary mechanical circulatory support found that VA ECMO in MI-related cardiogenic shock did not improve 6-month outcomes versus standard care, reinforcing the need for careful patient selection (PMID 39236726).

Differences from Cardiopulmonary Bypass

• Fishman's Pulmonary Diseases and Disorders (Ch. 149 - ECMO in Acute Respiratory Failure)
• Fischer's Mastery of Surgery, 8th Ed. (p. 346 - VA ECMO in Cardiovascular Support)
• StatPearls: ECMO in Adults