EXTRACORPOREAL MEMBRANE OXYGENATION (ECMO)

MD Anaesthesia PG Examination - 30 Marks

DEFINITION AND INTRODUCTION

• 1953: Dr. John Gibbon - first heart-lung machine for open heart surgery
• 1972: Dr. J.D. Hill - first successful prolonged extracorporeal support in an adult (75 hours) for post-trauma respiratory failure
• 1975: Dr. Robert Bartlett ("father of modern ECMO") - saved a neonate with meconium aspiration syndrome
• 2009: H1N1 influenza pandemic - landmark expansion of adult ECMO use; CESAR trial demonstrated 63% vs 47% survival with ECMO vs standard therapy
• Miller's Anesthesia, 10e; Sabiston Textbook of Surgery

CIRCUIT COMPONENTS

TYPES / CONFIGURATIONS OF ECMO

1. Venovenous ECMO (VV ECMO)

• Drainage: Femoral vein or IJV (or dual-lumen single cannula in IJV - "Avalon" cannula)
• Return: Internal jugular vein → right atrium
• Function: Respiratory support ONLY - oxygenates blood and removes CO2; requires intact cardiac function
• Hemodynamic effect: Does NOT increase cardiac output; may slightly reduce afterload via vasodilation on initiation

2. Venoarterial ECMO (VA ECMO)

• Drainage: Femoral vein / right atrium
• Return: Femoral artery / aorta (peripheral) or aorta/axillary artery (central)
• Function: Biventricular cardiac support AND respiratory support
• Hemodynamic effect: Increases MAP, reduces preload, increases systemic afterload; provides circulatory support independent of cardiac function

3. Veno-Arterio-Venous ECMO (V-AV ECMO) - Hybrid

• Returns blood to BOTH arterial and venous circulations
• Used when patient needs both respiratory and cardiac support simultaneously, or transitioning between modalities

4. Parallel / Dual-circuit ECMO

• Two separate ECMO circuits used when one circuit is insufficient
• Used in high cardiac output states (sepsis) or severe refractory hypoxia
• Risk of recirculation between circuits

INDICATIONS

VV ECMO - Respiratory Failure

VA ECMO - Cardiac Failure

• Miller's Anesthesia, 10e, p. 12118; Sabiston Textbook of Surgery, p. 2654

CONTRAINDICATIONS

• Irreversible condition with no possibility of recovery, transplant, or destination therapy
• Severe aortic regurgitation (VA ECMO increases afterload, worsens AR and prevents LV ejection)
• Advanced age with multiple comorbidities and no bridge therapy planned

• Chronic terminal illness / poor baseline quality of life
• Severe neurological injury / prolonged low-flow cardiac arrest
• Prolonged mechanical ventilation (>7 days) before ECMO consideration
• Active non-compressible bleeding (especially intracranial haemorrhage)
• Severe peripheral vascular disease (for peripheral cannulation)
• Morbid obesity

CANNULATION

Peripheral (bedside, percutaneous - most common)

• Performed at bedside without surgical exposure
• Seldinger technique under fluoroscopic/echocardiographic guidance
• VV ECMO sites: Femoral vein (drainage) + right IJV (return); OR dual-lumen Avalon cannula in right IJV
• VA ECMO sites: Femoral vein (drainage) + femoral artery (return) + separate distal perfusion cannula in superficial femoral artery to prevent limb ischaemia

Central (surgical, intraoperative)

• Requires sternotomy or thoracotomy
• Direct aortic/right atrial cannulation (as in CPB)
• Reserved for postcardiotomy cases, intraoperative use, or when peripheral access is impractical
• Advantages: larger cannulas, better flows, avoids Harlequin syndrome

• Subcostal view confirms guidewire position in IVC/RA junction
• Guides cannula tip placement and confirms position
• Detects pericardial effusion, cardiac thrombus, AR (contraindication to VA), LV distension on VA ECMO

MANAGEMENT ON ECMO

VV ECMO Management

• Tidal volume: 4-6 mL/kg predicted body weight
• Plateau pressure: <25 cmH2O
• Driving pressure: <15 cmH2O
• PEEP: 10 cmH2O
• RR: 10 breaths/min
• FiO2: 40%

• Target SaO2 >88-92%
• ECMO blood flow typically 3-5 L/min
• Oxygenation determined by: ECMO flow rate, FiO2 on sweep gas, haemoglobin level, cardiac output (ECMOBF/CO ratio)
• CO2 removal: controlled primarily by sweep gas flow rate (increase sweep = more CO2 removed)

• Unfractionated heparin continuous infusion - target aPTT 60-80 seconds OR anti-Xa 0.3-0.7 IU/mL
• Antithrombin III (AT-III) supplementation if heparin resistance occurs
• Monitor ACT, aPTT, TEG/ROTEM

• Reinfused oxygenated blood re-enters drainage cannula without entering patient's circulation
• Recognised by: high SaO2 at pump inlet, no improvement in patient oxygenation
• Management: reposition cannulas (increase distance between drainage and return), reduce pump speed, add second drainage cannula, change to dual-lumen cannula

• Check oxygenator function (replace if P50 or pre/post oxygenator PaO2 difference reduced)
• Increase pump flow rates
• Treat recirculation
• If cardiac output very high (sepsis) - flow may be insufficient fraction of total CO

VA ECMO Management

1. Intra-aortic balloon pump (IABP) - reduces afterload, improves coronary perfusion
2. Impella device - directly drains LV into aorta
3. Atrial septostomy (blade or balloon) - creates interatrial communication
4. Surgical vent in LA/LV during open surgery

• Sabiston Textbook of Surgery, p. 2661

SPECIAL SITUATION: HARLEQUIN SYNDROME (North-South Syndrome)

• Increase ECMO flow to push mixing zone towards aortic arch
• Reduce inotropes to decrease native cardiac output
• Aggressive volume removal
• Convert to central cannulation
• Add second return cannula in IJV (VAV-ECMO configuration)
• Optimise mechanical ventilation to improve native lung function

PHARMACOKINETICS ON ECMO

• Sequestration: Lipophilic drugs (e.g., fentanyl, midazolam, propofol) are adsorbed onto the circuit tubing and oxygenator - substantially reduced plasma levels; dose requirements increase
• Volume of distribution: Increased due to circuit prime volume and haemodilution
• Protein binding: Altered; affects drug distribution
• Practical: Increase initial doses of sedatives and opioids; monitor drug levels where possible

WEANING FROM ECMO

Weaning VV ECMO

1. Wean sweep gas FiO2 first (to 21%), then reduce sweep gas flow rate
2. Wean ventilator FiO2 simultaneously
3. Decannulation thresholds: FiO2 <50%, PEEP <10 cmH2O, compliance >50 mL/cmH2O, RR <20 breaths/min - sustained for ≥48 hours
4. Trial of "clamping" sweep gas with the circuit still running to test native lung function
5. Consider ECCO2R (extracorporeal CO2 removal at low flows) as transition if CO2 removal but not oxygenation needed

Weaning VA ECMO

1. Gradually reduce ECMO flow (by 0.5 L/min increments)
2. Monitor haemodynamics at each step
3. At flows of 1-1.5 L/min, assess feasibility of decannulation
4. Maintain anticoagulation until cannula removal

Decannulation

• Peripheral: cannulas removed, manual compression or surgical closure
• Post-decannulation: limb Doppler, venous duplex for DVT at 24h
• If decannulation fails: bridge to LVAD/transplant, or palliation discussion

COMPLICATIONS

Patient-related Complications

Circuit/Mechanical Complications

• Sabiston Textbook of Surgery, p. 2665-2666

ANTICOAGULATION IN ECMO

• Heparin infusion is the standard; titrated to aPTT 60-80 sec or anti-Xa 0.3-0.7 IU/mL
• AT-III deficiency causes heparin resistance - supplement AT-III or use bivalirudin
• Bivalirudin - alternative in heparin-induced thrombocytopenia (HIT)
• No anticoagulation ECMO - short runs or high bleeding risk; evidence emerging but not standard
• Monitor: ACT, aPTT, anti-Xa, platelet count, fibrinogen, TEG/ROTEM
• Target platelet count >80,000/µL; fibrinogen >200 mg/dL

ECMO IN SPECIFIC SCENARIOS (Anaesthesia Context)

ECPR (Extracorporeal CPR)

• ECMO initiated during CPR for refractory in-hospital cardiac arrest
• Requires rapid cannulation team (ideally within 60 minutes of arrest)
• Best outcomes: witnessed arrest, CPR duration <60 min, reversible cause, age <65 years
• ELSO guidelines recommend consideration when conventional CPR fails within 10-15 minutes

ECMO During Lung Transplantation

• VA ECMO preferred intraoperatively (surgical manipulation causes haemodynamic instability + one-lung ventilation in end-stage lung disease)
• Advantages over CPB: less inflammatory response, less primary graft dysfunction (PGD), better short and long-term outcomes
• Post-transplant: VV or VA ECMO for PGD, RV failure, LV failure

ECMO During High-Risk Cardiac Procedures

• Pre-procedural prophylactic ECMO support for high-risk PCI
• Anaesthetic consideration: arterial line in right radial artery (for upper body ABG in VA ECMO), central venous access, invasive haemodynamic monitoring

ELSO (EXTRACORPOREAL LIFE SUPPORT ORGANISATION) GUIDELINES - KEY POINTS

ANAESTHESIA CONSIDERATIONS - KEY POINTS FOR EXAM

1. Monitoring: Invasive arterial line in right radial artery for VA ECMO (best proxy for upper body oxygenation, especially in Harlequin syndrome); additional CVP, PA catheter or TOE/TTE
2. Drug dosing: Significantly increased doses of lipophilic drugs (fentanyl, propofol, midazolam) due to circuit sequestration; monitor drug levels
3. Lung rest ventilation: Ultra-protective on VV ECMO (Vt 4-6 mL/kg, plateau <25 cmH2O, driving pressure <15 cmH2O)
4. LV distension on VA ECMO: Recognised by loss of arterial pulse pressure; treat with IABP/Impella/septostomy
5. Anticoagulation: Continuous heparin; frequent monitoring; reverse with protamine at decannulation
6. Temperature: Heat exchanger in circuit; avoid hyperthermia (increases O2 demand) and hypothermia (coagulopathy, arrhythmia)
7. Recirculation in VV ECMO: Suspected when circuit looks "too red" or patient not improving; managed by repositioning cannulas

SUMMARY TABLE: VV vs VA ECMO

REFERENCES (Textbook Sources)

• Miller's Anesthesia, 10e - Chapters 49, 81, 33
• Sabiston Textbook of Surgery - Chapter 116
• Fishman's Pulmonary Diseases and Disorders - Chapter 31
• Current Surgical Therapy, 14e
• Murray & Nadel's Textbook of Respiratory Medicine