Extracorporeal Membrane Oxygenation (ECMO)

What Is ECMO?

Basic Circuit Components

1. Inflow (drainage) cannula - drains venous blood from the patient
2. Centrifugal pump - magnetically levitated disc that creates a vortex; preload-dependent and afterload-sensitive
3. Membrane oxygenator - thousands of hollow-bore microtubules through which oxygen flows; blood oxygenation occurs across a 2 m² surface (vs. 91-118 m² in the human lung)
4. Outflow (return) cannula - returns oxygenated blood to the patient

Types of ECMO

VV ECMO (Veno-Venous)

• Drains blood from a vein and returns it to a vein (typically femoral/internal jugular)
• Provides pulmonary support only - no hemodynamic support
• Primary modality for isolated ARDS and acute respiratory failure
• Requires adequate native cardiac function

VA ECMO (Veno-Arterial)

• Drains venous blood and returns oxygenated blood into the arterial system (usually femoral artery)
• Provides both cardiac and pulmonary support
• Indicated for cardiogenic shock, cardiac arrest, biventricular failure, myocarditis, myocardial stunning
• Can cause left ventricular fluid overload and pulmonary edema because it does not unload the LV - often requires additional LV venting strategies (inotropes, IABP, Impella)

VAV ECMO (Veno-Arterio-Venous)

• Hybrid configuration used when ARF is accompanied by biventricular failure

RVAD-ECMO (Protek Duo)

• Cannula traverses the tricuspid and pulmonic valves; drains from SVC/right atrium and returns blood to the pulmonary artery
• Used for isolated RV failure with ARDS - provides both RV support and oxygenation

Indications

ECMO Gas Exchange Physiology

• The oxygenator is very efficient at CO2 removal - complete CO2 removal can be achieved with high sweep gas flows at blood flow rates <1 L/min
• Oxygenation requires higher flows - approximately 4 L/min must be maintained to achieve adequate O2 delivery (~260 mL O2/min), with post-oxygenator PaO2 >300 mmHg
• Pre- and post-membrane pressure sensors monitor oxygenator function; a normal transmembrane pressure drop should not exceed 30 mmHg

Anticoagulation

Complications

Bleeding

• Most common complication - caused by anticoagulation, thrombocytopenia, mechanical platelet destruction, loss of clotting factors
• Common sites: epistaxis, GI bleeding
• Rare but severe: intracranial hemorrhage, pulmonary hemorrhage

Thrombotic

• Activation of neutrophils, monocytes, leukocytes in the circuit
• Risk of clot formation in the circuit (oxygenator thrombosis)
• Occasional cytokine storm

Vascular

• Arterial injury, pneumothorax during cannulation
• Mitigated by ultrasound-guided access, TEE guidance, echocardiography

LV-specific (VA ECMO)

• Pulmonary edema and LV fluid overload - because VA ECMO increases afterload on an already impaired LV without providing direct LV unloading

Cannulation and Monitoring

• Ultrasound guidance is mandatory for percutaneous vascular access
• Transesophageal echocardiography (TEE) should be performed before and during cannulation to:
  • Assess RV and LV function
  • Rule out patent foramen ovale, ASD, VSD (which would cause recirculation)
  • Detect pericardial effusion
  • Guide cannula tip positioning
• Fluoroscopy is also used, especially for PA cannulas (Protek Duo)
• Transmembrane pressure monitoring and flow monitoring are standard of care

Weaning and Discontinuation

1. Bridge to recovery - days to weeks; device removed when native cardiac/pulmonary function recovers
2. Bridge to durable device - transition to LVAD or BiVAD
3. Bridge to transplant - heart or lung transplant

Recent Evidence (2024-2026)