ECMO: Types, Mechanism, Indications, Contraindications and Complications

1. Types of ECMO

2. Mechanism of action

1. Venous blood drainage: Deoxygenated blood is removed through a large venous cannula.
2. Pump: A centrifugal pump drives blood through the extracorporeal circuit.
3. Membrane oxygenator: Blood passes across a semipermeable membrane:
   • Oxygen diffuses into blood.
   • Carbon dioxide diffuses out of blood.
4. Heat exchanger: Maintains blood temperature.
5. Return of blood:
   • VV-ECMO returns oxygenated blood to the venous system. The heart then pumps it to the body.
   • VA-ECMO returns oxygenated blood directly to the arterial circulation, thereby supporting cardiac output and organ perfusion.

3. Indications

A. VV-ECMO: Severe respiratory failure

• Severe ARDS, especially with refractory hypoxaemia
  • PaO₂/FiO₂ <100 despite adequate PEEP and prone ventilation
• Severe hypercapnic respiratory failure with acidosis despite ventilation
• Viral or bacterial pneumonia, including severe influenza/COVID-related ARDS
• Aspiration pneumonitis
• Severe status asthmaticus with life-threatening hypercapnia
• Bridge to lung transplantation
• Primary graft dysfunction after lung transplant

B. VA-ECMO: Cardiac or cardiopulmonary failure

• Cardiogenic shock due to acute myocardial infarction
• Fulminant myocarditis
• Acute decompensated heart failure or severe biventricular failure
• Post-cardiotomy cardiogenic shock, failure to wean from cardiopulmonary bypass
• Massive pulmonary embolism with shock or cardiac arrest
• Refractory ventricular arrhythmias
• Cardiac arrest refractory to conventional CPR, termed ECPR
• Bridge to recovery, LVAD, heart transplantation, or decision

4. Contraindications

Major contraindications

• Irreversible cardiac or pulmonary disease without an option for transplant, LVAD, or other definitive therapy
• Terminal malignancy or severe irreversible comorbidity with limited life expectancy
• Severe irreversible neurological injury
• Active uncontrolled major bleeding
• Severe uncorrectable coagulopathy or inability to anticoagulate
• Acute intracranial hemorrhage or massive ischemic stroke
• Prolonged unwitnessed cardiac arrest or very long no-flow/low-flow time
• Advanced irreversible multiorgan failure
• Severe aortic regurgitation for VA-ECMO
• Aortic dissection, especially for peripheral VA-ECMO
• Severe peripheral vascular disease that prevents safe arterial cannulation

5. Complications

A. Hematological

• Bleeding, especially at cannulation or surgical sites, gastrointestinal tract, lungs, or intracranially
• Thrombocytopenia and coagulopathy
• Circuit thrombosis or oxygenator thrombosis
• Disseminated intravascular coagulation
• Hemolysis due to mechanical shear stress

B. Vascular and cardiac

• Limb ischemia, particularly with femoral arterial VA-ECMO cannulation
• Compartment syndrome and possible limb loss
• Arterial injury, dissection, pseudoaneurysm, hematoma
• Venous thrombosis and deep-vein thrombosis
• Left ventricular distension and pulmonary edema in VA-ECMO
• Differential hypoxaemia in peripheral VA-ECMO, called Harlequin syndrome or north-south syndrome

C. Neurologic

• Ischemic stroke
• Intracranial hemorrhage
• Seizures
• Hypoxic-ischemic brain injury, especially after cardiac arrest

D. Infective and organ complications

• Cannula-site infection, bacteremia, sepsis
• Acute kidney injury and need for renal replacement therapy
• Liver dysfunction
• Pulmonary edema or hemorrhage
• Pressure injuries, critical illness myopathy, and delirium

E. Mechanical circuit complications

• Cannula malposition or dislodgement
• Low-flow states or "chatter/chugging"
• Air embolism
• Pump failure
• Oxygenator failure
• Tubing rupture or circuit clotting

Conclusion

• VV-ECMO is for isolated severe respiratory failure.
• VA-ECMO is for cardiac failure with or without respiratory failure.
• ECMO is a temporary rescue therapy, not definitive treatment. Its benefit depends on a reversible disease process or a clear pathway to transplant or durable mechanical support.