What are the indications for venoarterial (VA) ECMO versus venovenous (VV) ECMO?

Indications for Venoarterial (VA) ECMO versus Venovenous (VV) ECMO

VV ECMO is indicated for isolated severe respiratory failure when the heart is functioning adequately, while VA ECMO is reserved for combined cardiopulmonary failure or cardiogenic shock requiring hemodynamic support. 1

VV ECMO: Respiratory Support Only

VV ECMO provides isolated pulmonary support by draining blood from the venous system, oxygenating it, and returning it to the venous circulation. 1 This configuration does not provide cardiac support and requires adequate native cardiac function to circulate the oxygenated blood.

Primary Indications for VV ECMO:

• Severe ARDS with PaO₂/FiO₂ < 80 mmHg for ≥3 hours despite optimal ventilation 2
• PaO₂/FiO₂ < 70 for ≥3 hours or < 100 for ≥6 hours despite optimization 2
• Plateau pressure > 28 cmH₂O for ≥6 hours despite lung-protective ventilation 2
• Refractory hypoxemia or hypercapnia in acute respiratory failure after maximal conventional therapies have failed 3
• Respiratory failure from ARDS, pneumonia, trauma, or primary graft failure following lung transplantation 4

Critical Prerequisites for VV ECMO:

• Must be initiated within 7 days of respiratory failure onset for optimal outcomes 2, 5
• All conventional therapies must be exhausted first: lung-protective ventilation (VT = 6 mL/kg PBW), PEEP ≥12 cmH₂O, prone positioning, and neuromuscular blockade 2, 5
• Patient must have adequate cardiac function - if requiring norepinephrine >0.5 µg/kg/min or significant inotropic support, VA ECMO should be considered instead 1, 2

VA ECMO: Combined Cardiopulmonary Support

VA ECMO drains blood from the venous system, oxygenates it, and actively pumps it into the arterial circulation, providing both respiratory support and hemodynamic stability. 1 This configuration can deliver up to 7 L/min of flow and completely replace cardiac output if needed.

Primary Indications for VA ECMO:

• Cardiogenic shock with very low cardiac output and reduced LV ejection fraction confirmed by echocardiography 1, 2
• Requirement for significant inotropic support and/or norepinephrine at dosages >0.5 µg/kg/min 1, 2
• Post-cardiotomy shock, post-heart transplant failure, or severe cardiac failure from any cause (cardiomyopathy, myocarditis, acute coronary syndrome with cardiogenic shock) 4
• Extracorporeal cardiopulmonary resuscitation (ECPR) for refractory cardiac arrest 3
• ARDS combined with severe cardiogenic shock 1

Key Distinguishing Features:

The critical decision point is cardiac function. 1, 2 If echocardiography demonstrates adequate cardiac output and the patient is hemodynamically stable on minimal vasopressor support (norepinephrine ≤0.5 µg/kg/min), VV ECMO is appropriate for isolated respiratory failure. 1, 2 If cardiac dysfunction is present with evidence of shock requiring high-dose vasopressors or inotropes, VA ECMO is necessary. 1, 2

Clinical Decision Algorithm:

1. Assess cardiac function via echocardiography 1, 2

   • Normal LV ejection fraction + minimal vasopressor needs → Consider VV ECMO for respiratory failure
   • Reduced LV ejection fraction + high vasopressor/inotrope requirements → VA ECMO indicated

2. Evaluate for right ventricular overload 2

   • Pulmonary artery systolic pressure >40 mmHg with acute cor pulmonale may benefit from VV ECMO to unload the RV 1, 2

3. Consider renal function 6

   • Patients requiring renal replacement therapy prior to ECMO may be better served by VA ECMO 6

Common Pitfalls to Avoid:

• Do not delay VA ECMO in patients with combined cardiopulmonary failure - attempting VV ECMO in a patient with inadequate cardiac output will fail to provide adequate tissue perfusion despite improved oxygenation 1, 4
• Do not initiate ECMO before optimizing conventional therapies - this includes lung-protective ventilation, prone positioning, and neuromuscular blockade for respiratory failure 2, 5
• Do not use VV ECMO if the patient requires renal replacement therapy and hemodynamic support - VA ECMO is more appropriate 6
• Avoid prolonged mechanical ventilation (>9.6 days) before ECMO consideration - this is associated with worse outcomes 2

Institutional Requirements:

ECMO should only be performed at centers with sufficient experience, volume, and expertise. 1, 2 Centers caring for more than 20-25 ECMO cases per year have significantly better outcomes than lower-volume centers. 1, 2 The learning curve requires at least 20 cases for optimal competence. 2

Monitoring Differences:

Both configurations require continuous arterial blood pressure monitoring, repeated echocardiography, and daily fluid balance tracking. 1, 2 However, VA ECMO requires more intensive hemodynamic monitoring including continuous ECMO flow recording since the device is providing cardiac output. 1 Thermodilution-based and pulse contour analysis-based cardiac output monitoring are unreliable during ECMO. 1

Complications:

Both VV and VA ECMO carry high risks of bleeding and thrombotic complications. 1 Recent data shows 42% of VV-ECMO patients experience thrombotic events, 37% experience bleeding events, and 21% experience both. 1 Almost all ECMO patients develop acquired von Willebrand syndrome (AVWS) within hours of device implantation, which may contribute to bleeding complications. 1, 2