What is the difference between Veno-Arterial (VA) and Veno-Venous (VV) Extracorporeal Membrane Oxygenation (ECMO)?

Difference Between VA and VV ECMO

The fundamental difference between VA and VV ECMO is that VA ECMO provides both cardiac and respiratory support, while VV ECMO provides only respiratory support without hemodynamic assistance. 1

Basic Configurations and Indications

VA ECMO (Veno-Arterial)

• Primary Function: Provides both cardiac and respiratory support
• Cannulation:
  • Blood is drained from the right atrium via a femoral venous or internal jugular venous cannula
  • After oxygenation, blood is returned to the arterial system (femoral, subclavian, or directly into aorta)
• Flow Capacity: Can pump up to 7 L/min for full or partial cardiopulmonary support 1
• Primary Indications:
  • Cardiogenic shock
  • Cardiac arrest
  • Bridge to recovery from cardiac failure
  • Bridge to transplantation
  • Adjunct therapy during cardiopulmonary resuscitation 1

VV ECMO (Veno-Venous)

• Primary Function: Provides respiratory support only
• Cannulation:
  • Blood is drained from the venae cavae via femoral or right internal jugular venous cannula
  • After oxygenation, blood is returned to the venous system
  • Can use a single bicaval double-lumen cannula in the internal jugular vein
• Primary Indications:
  • Severe respiratory failure
  • Bridge to recovery of pulmonary function
  • Bridge to lung transplantation 1

Physiological Effects

VA ECMO

• Reduces cardiac preload
• Provides systemic perfusion
• Reduces cardiac workload
• Delivers oxygenated blood to coronary circulation
• Can fully replace cardiac function if needed 2
• May increase left ventricular afterload

VV ECMO

• Improves systemic oxygenation
• Facilitates CO₂ removal
• Reduces ventilator-induced lung injury by allowing lung-protective ventilation
• Indirectly supports right ventricular function by:
  • Reducing pulmonary vascular resistance
  • Improving oxygenation to the RV
  • Reducing RV wall tension 2
• Does not provide direct circulatory support

Clinical Decision Making

When deciding between VA and VV ECMO:

1. For isolated respiratory failure:

   • VV ECMO is the preferred initial configuration, even if mild shock is present 2, 3
   • Survival rates are better with VV ECMO (58%) compared to VA ECMO (43%) in ARDS patients 3

2. For primary cardiac failure or combined cardiopulmonary failure:

   • VA ECMO is indicated 2

3. For patients with respiratory failure who develop hemodynamic compromise during VV ECMO:

   • Consider conversion to hybrid configurations (VVA ECMO) 4

4. For patients on VA ECMO who develop respiratory failure with some cardiac function:

   • Consider adding a venous reinfusion limb (VAV ECMO) to improve oxygen delivery to cerebral and coronary circulation 4

Complications

VA ECMO

• Arterial vascular complications
• Left ventricular distention
• Differential hypoxemia ("North-South syndrome")
• Higher risk of stroke
• Higher risk of hemolysis 3

VV ECMO

• Lower rates of gastrointestinal bleeding and hemolysis compared to VA ECMO 3
• Recirculation issues (oxygenated blood returns to the circuit without systemic circulation)
• Insufficient for severe hemodynamic compromise

Monitoring Considerations

• VA ECMO: Monitor arterial waveform pulsatility to assess myocardial function, preload adequacy, and potential LV overload 2
• VV ECMO: Focus on oxygenation parameters and right ventricular function

Important Caveats

• Approximately 4% of patients initially placed on VV ECMO require conversion to VA ECMO due to development of hemodynamic instability 3
• ECMO should be performed at experienced centers with sufficient volume (>20-25 cases/year) to maintain competence 1
• Both configurations require anticoagulation, which carries risks of bleeding and thrombotic complications 1, 5
• The decision between VA and VV ECMO should be made by experienced clinicians at centers with robust expertise in ECMO management 1