ECMO (Extracorporeal Membrane Oxygenation) - DNB Final Theory Answer (10 Marks)

Definition

ECMO (also called Extracorporeal Life Support / ECLS) is a form of prolonged cardiopulmonary support where blood is drained from the patient, oxygenated and decarbonated outside the body via an artificial membrane lung, and returned to the patient. It is used when conventional therapy fails for severe, potentially reversible cardiac and/or respiratory failure.

Basic Circuit Components

The circuit has 4 key parts:

Component	Function
Inflow (drainage) cannula	Drains venous blood from patient into circuit
Centrifugal pump	Propels blood through the circuit
Membrane oxygenator	Adds O2 and removes CO2 (mimics lung)
Outflow (return) cannula	Returns blood to patient (vein or artery)

Heparin is infused continuously into the circuit to prevent clotting.

Types of ECMO

1. Veno-Venous (VV) ECMO

Blood drained from a vein, returned to a vein
Provides respiratory support only - does NOT support cardiac function
Most common configuration: right femoral vein (inflow) + right internal jugular vein (outflow)
An alternative: dual-lumen single cannula via right IJV
Used for: severe ARDS, refractory respiratory failure (without cardiac dysfunction)

2. Veno-Arterial (VA) ECMO

Blood drained from a vein, returned to an artery (usually femoral artery)
Provides both cardiac AND respiratory support - bypasses the heart and lungs
Used for: cardiogenic shock, cardiac arrest, biventricular failure, refractory hypoxemia with cardiac dysfunction
Risk: can cause pulmonary edema and LV distension because it does not directly unload the LV - may need additional LV unloading (IABP or Impella)

Indications

VV ECMO (Respiratory)

Severe ARDS with PaO2/FiO2 < 80 mmHg despite optimal mechanical ventilation
Severe hypercapnia (pH < 7.15) unresponsive to ventilation
Life-threatening air leak syndromes
Bridge to lung transplantation
ECMO threshold: Murray Lung Injury Score > 3 or pH < 7.2 despite 6 hours of optimization

VA ECMO (Cardiac)

Cardiogenic shock unresponsive to inotropes/vasopressors
Cardiac arrest refractory to CPR (E-CPR)
Myocarditis with acute severe cardiac failure
Post-cardiotomy cardiogenic shock
High-risk PCI or cardiac surgery

Contraindications

Absolute:

Irreversible/terminal illness (no bridge goal)
Severe, irreversible neurologic injury
Aortic dissection (for VA ECMO)

Relative:

Prolonged CPR without perfusion (>60 min)
Advanced age with multiple comorbidities
Severe peripheral vascular disease (limits femoral access)
Active bleeding or coagulopathy (anticoagulation required)
Immunosuppression (high infection risk)

Monitoring on ECMO

Circuit flow: 60-80 mL/kg/min for VV; target adequate cardiac output for VA
Sweep gas (FiO2 + flow rate): controls CO2 removal - increase sweep to reduce PaCO2
Pre- and post-oxygenator blood gases
ACT / anti-Xa levels for heparin titration
Daily circuit inspection for clots, raceway tears
SaO2 monitoring: in VV ECMO, SpO2 of 85-92% is acceptable ("permissive hypoxemia")

"Lung Rest" Strategy on ECMO

Once on VV ECMO, the ventilator is set to very low, non-injurious settings to allow the lungs to recover:

Low tidal volume (4 mL/kg)
Low RR (10/min)
Low PEEP (5-10 cmH2O)
Low FiO2 (0.3-0.4)

This prevents ventilator-induced lung injury (VILI) while the lungs heal.

Complications

Category	Complication
Bleeding	Cannula site bleeding, intracranial hemorrhage (from anticoagulation)
Thrombosis	Circuit clots, stroke, limb ischemia
Infection	Cannula-site infection, bloodstream infection
Cardiac (VA)	LV distension, pulmonary edema - "North-South syndrome"
Limb ischemia	Distal limb ischemia from arterial cannula (VA ECMO) - needs distal perfusion cannula
Hemolysis	Due to shear stress across the pump
Recirculation	In VV ECMO - oxygenated blood re-enters the inflow cannula
Air embolism	Circuit breach

Key Trials (Important for Exam)

Trial	Year	Findings
CESAR	2009	ECMO at specialist center improved survival/disability-free survival in severe ARDS vs conventional ventilation
EOLIA	2018	No significant 60-day mortality difference (VV ECMO vs control), BUT 28% crossover to ECMO in control group - Bayesian analysis favored ECMO

Weaning from ECMO

VV ECMO: Gradually reduce sweep gas flow; if patient tolerates FiO2 1.0 on the circuit with sweep gas turned to near zero and SpO2 is maintained - ready to decannulate
VA ECMO: Wean by gradually reducing flow (by 0.5-1 L/min increments); reassess cardiac function by echo at each step

Summary Table: VV vs VA ECMO

Feature	VV ECMO	VA ECMO
Support provided	Lungs only	Heart + Lungs
Cannulation	Vein to Vein	Vein to Artery
Use in ARDS	Yes	No (unless + cardiac failure)
Cardiac output	Patient's own heart	Bypasses heart
LV unloading needed	No	Yes (often)
Risk of limb ischemia	Low	High (femoral artery)

One-Line Summary for Last-Minute Revision

ECMO = external heart-lung machine for severe, reversible cardiac/respiratory failure. VV for lungs only, VA for heart+lungs. Core circuit = drainage cannula + centrifugal pump + membrane oxygenator + return cannula. Main complications = bleeding, clotting, infection, LV distension (VA). Key trial = CESAR (VV ECMO improved outcomes in severe ARDS).

Sources: Fishman's Pulmonary Diseases and Disorders, Fischer's Mastery of Surgery 8th ed.

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