ECMO (Extracorporeal Membrane Oxygenation) - Short Notes

Definition

Basic Circuit

1. Inflow cannula - drains venous blood from the patient into the circuit
2. Centrifugal pump - maintains blood flow through the circuit
3. Membrane oxygenator - adds O₂ and removes CO₂
4. Outflow cannula - returns oxygenated blood to the patient

Types of ECMO

Hybrid Configurations

• V-AV (Veno-Arteriovenous): Combined respiratory and partial cardiac support; used when standard VV fails to maintain oxygenation in a patient with mild cardiac dysfunction

Indications

VV ECMO (Respiratory)

• Severe ARDS (PaO₂/FiO₂ < 80 despite optimal ventilation)
• Murray Lung Injury Score > 3.0 or pH < 7.20
• Refractory hypoxemia or hypercapnia
• Bridge to lung transplantation
• COVID-19-related severe ARDS

VA ECMO (Cardiac)

• Cardiogenic shock refractory to medical therapy
• Cardiac arrest (ECPR - extracorporeal CPR)
• Acute myocarditis or myocardial stunning
• Refractory arrhythmias
• Bridge to VAD (Ventricular Assist Device) or cardiac transplant
• Post-cardiotomy shock (failure to wean from bypass)

Cannulation

Central Cannulation

• Direct cannulation of large central vessels (usually via sternotomy)
• Reserved for patients already on cardiopulmonary bypass for cardiac surgery
• Allows higher flows but carries higher bleeding and infection rates

Peripheral Cannulation

• Preferred and most common approach
• Can be performed by non-surgeons (even at bedside)
• Uses peripheral vessels (femoral, jugular)
• Preferred VV cannulation sites: Right common femoral vein (inflow) + Right IJV (outflow)

ECMO vs. Cardiopulmonary Bypass

Management on ECMO

Ventilator settings (Lung-Rest Strategy)

• Reduce ventilator support to allow injured lungs to rest
• Low tidal volumes, low PEEP, low FiO₂

Anticoagulation

• Continuous heparin infusion (circuit thrombosis prevention)
• Target ACT 180-220 seconds or anti-Xa levels per institutional protocol
• Risk of bleeding vs. thrombosis must be balanced

Cardiovascular

• Maintain systemic perfusion with inotropes/vasopressors as needed
• Echocardiography to monitor LV function and volume status
• VA ECMO can cause LV afterload increase, pulmonary oedema - may need LV unloading (IABP, Impella)

Neurological

• Avoid paralytic agents; perform regular neurological exams
• Sedation vacations to assess CNS
• Serial head ultrasounds in neonates (screen for IVH)
• Aggressive treatment of seizures (phenobarbital)

Renal

• ~60% of ECMO patients require CRRT (Continuous Renal Replacement Therapy)
• Need for CRRT is associated with significantly increased mortality (17% vs 53% 3-month survival)

Contraindications

• Irreversible organ failure (when ECMO cannot serve as a bridge)
• Aortic dissection (VA ECMO)
• Severe aortic regurgitation (VA ECMO)

• Prolonged pre-ECMO CPR without adequate perfusion
• Uncontrolled bleeding or coagulopathy
• Advanced age with poor baseline functional status

Complications

Key Trials

• CESAR Trial (Peek et al., 2009): 180 adults with severe ARF. Referral to ECMO centre improved 6-month survival without severe disability (63% vs 47%) compared to conventional management.
• EOLIA Trial: RCT of VV ECMO vs conventional management in severe ARDS. Did not meet primary endpoint (60-day mortality), but high crossover rate (28%) confounded results. Bayesian reanalysis favoured ECMO.

Weaning from ECMO

• VV ECMO: Gradually reduce sweep gas flow; trial of "ECMO holiday" (clamping sweep gas while maintaining blood flow)
• VA ECMO: Gradual reduction in pump flow while monitoring haemodynamics and echo
• Decannulate when patient demonstrates ability to sustain adequate gas exchange and/or cardiac output independently