What is Extracorporeal Membrane Oxygenation (ECMO)?

What is Extracorporeal Membrane Oxygenation (ECMO)?

ECMO is a mechanical life support system that temporarily replaces the function of failing heart and/or lungs by oxygenating blood and removing carbon dioxide outside the body, providing critical time for these organs to recover from severe but potentially reversible cardiorespiratory failure. 1

Core Mechanism and Technology

ECMO functions as a modified heart-lung machine adapted for bedside use in intensive care settings, distinct from traditional cardiopulmonary bypass used during cardiac surgery. 1 The system drains blood from the patient's venous system, pumps it through a membrane oxygenator where gas exchange occurs (oxygen added, carbon dioxide removed), and returns the oxygenated blood to the patient's circulation. 1

Two Primary ECMO Configurations

Venovenous (VV) ECMO

• Primary indication: Severe respiratory failure requiring pulmonary support only 1, 2
• Blood pathway: Drains deoxygenated blood from venae cavae via femoral or internal jugular venous cannula, passes through membrane oxygenator, returns oxygenated blood to venous system 1
• Can use: Single bicaval double-lumen cannula inserted in internal jugular vein for both drainage and return 1
• Flow rates: High blood flow circuit providing full or partial extracorporeal pulmonary support 1
• Specific indication criteria: PaO₂/FiO₂ < 80 mmHg for at least 3 hours despite optimal ventilation, or < 100 for ≥6 hours, or plateau pressure > 28 cmH₂O for ≥6 hours despite lung-protective strategies 2

Venoarterial (VA) ECMO

• Primary indication: Severe cardiogenic shock requiring both cardiac and respiratory support 1, 2
• Blood pathway: Drains blood from right atrium via femoral/internal jugular venous cannula (or directly from right atrium if open chest), pumps through oxygenator, actively returns blood into arterial system via femoral/subclavian artery cannula or directly into aorta 1
• Flow rates: High blood flow circuit up to 7 L/min providing full or partial cardiopulmonary support 1
• Specific indication criteria: Very low cardiac output with reduced LV ejection fraction requiring significant inotropic support and/or norepinephrine >0.5 µg/kg/min 2

Clinical Role and Positioning

ECMO does not cure underlying disease but buys time for organ recovery while preventing further damage. 3 In respiratory failure, ECMO enables "lung rest" by minimizing ventilator-induced lung injury through reduced ventilator settings while maintaining adequate gas exchange. 4 The technology should be considered a rescue therapy after conventional medical therapies have failed or are likely to fail. 2

Critical Timing Considerations

VV-ECMO should be initiated within 7 days of respiratory failure onset for optimal outcomes, with early consideration recommended before irreversible end-organ damage occurs. 2, 5 Prolonged mechanical ventilation (>9.6 days) before ECMO consideration is associated with worse outcomes. 2 For VA-ECMO in cardiac arrest (ECPR), rapid initiation is essential to prevent further decompensation and improve neurologic outcomes. 6

Institutional Requirements and Safety

ECMO is a complex, high-risk, and costly modality that should only be performed at centers with sufficient experience, volume, and expertise. 1, 2 Centers caring for more than 20-25 ECMO cases per year have significantly better outcomes than lower-volume centers. 2 The learning curve requires at least 20 cases to establish competence, with a recommended minimum annual volume of 20 cases per year for the entire center. 2

Essential institutional requirements include:

• Multidisciplinary ECMO team available 24/7 2
• Quality assurance review procedures 2
• Team composition including intensivists, pulmonologists, respiratory therapists, and specialized nursing staff 5
• Mobile ECMO teams for patient retrieval from non-ECMO centers 2

Major Complications and Risks

Bleeding complications are common and associated with high mortality rates, particularly intracranial hemorrhage. 2 Acquired von Willebrand Syndrome (AVWS) develops in almost all ECMO patients within hours of device implantation and contributes to bleeding risk. 2 Thrombotic and thromboembolic complications can occur despite anticoagulation. 2 Contraindications to anticoagulation represent an absolute contraindication to ECMO. 2

Patient Selection Factors

Factors supporting ECMO use include:

• Young age with fewer comorbidities 2
• Potentially reversible etiology of cardiorespiratory failure 2, 3
• Failure of less invasive rescue therapies (inhaled nitric oxide/prostacyclin, prone positioning, neuromuscular blockade, corticosteroids) 5
• Evidence of right ventricular overload with pulmonary artery systolic pressure > 40 mmHg and acute cor pulmonale on echocardiography 2

Current Evidence Limitations

Given the need for further evidence, restraint in widespread use of ECMO is encouraged until better appreciation exists for both potential clinical applications and optimal techniques. 1 The evidence supporting ECMO use in some indications remains limited, and further clinical trials are essential for identifying and clarifying indications, contraindications, and techniques. 1, 2 Hospitals without ECMO capability should establish institutional guidelines to identify ECMO-eligible patients and relationships with ECMO-capable institutions for timely transfer. 2, 5