Extracorporeal Membrane Oxygenation (ECMO)
Extracorporeal Membrane Oxygenation (ECMO) is a temporary life support system designed to provide cardiac and/or respiratory support for patients with severe but potentially reversible heart or lung failure that is refractory to conventional treatment. 1
Definition and Basic Components
ECMO is a form of extracorporeal life support (ECLS) that differs from cardiopulmonary bypass systems used in surgery by being configured for more prolonged support. The system consists of:
- Centrifugal pump
- Membrane oxygenator
- Inlet and outlet cannulas
- Control and monitoring system
- Heparin-coated circuit 1
Types of ECMO
There are two primary configurations of ECMO:
1. Veno-Venous (VV) ECMO
- Purpose: Provides respiratory support only
- Configuration: Blood is drained from the venae cavae via femoral or right internal jugular venous cannula, oxygenated, and returned to the venous system
- Flow: High blood flow (up to 7 L/min)
- Requirements: Requires adequate cardiac function to maintain circulation
- Primary indications: Severe respiratory failure, bridge to recovery of pulmonary function, bridge to lung transplantation 1, 2
2. Veno-Arterial (VA) ECMO
- Purpose: Provides both cardiac and respiratory support
- Configuration: Blood is drained from the right atrium and returned to the arterial system (femoral, subclavian, or directly into the aorta)
- Flow: Can pump up to 7 L/min for total or partial cardiopulmonary support
- Effects: Reduces ventricular preload and increases systemic perfusion
- Primary indications: Cardiogenic shock, cardiac arrest, bridge to recovery from cardiac failure, bridge to transplantation, adjunct therapy during cardiopulmonary resuscitation 1, 2
Additional Configuration
Extracorporeal Carbon Dioxide Removal (ECCO2R)
- Uses a venovenous (or arteriovenous) extracorporeal device at low blood flows
- Primarily focused on CO2 removal rather than oxygenation 2
Indications
VA ECMO Indications
- Refractory cardiogenic shock
- Cardiac arrest (ECPR - extracorporeal cardiopulmonary resuscitation)
- Bridge to cardiac recovery
- Bridge to heart transplantation or ventricular assist device
- Post-cardiotomy shock 1, 3
VV ECMO Indications
- Severe acute respiratory failure refractory to conventional ventilation
- Refractory hypoxemia or hypercapnia despite maximal conventional therapies
- Bridge to lung recovery
- Bridge to lung transplantation 1, 3
Complications and Risks
ECMO is associated with significant complications that can impact morbidity and mortality:
| Complication | VA ECMO | VV ECMO |
|---|---|---|
| Stroke | Higher risk | Lower risk |
| Hemolysis | Higher risk | Lower risk |
| Left ventricular distention | Higher risk | Lower risk |
| Recirculation issues | Lower risk | Higher risk |
| Insufficient support for severe hemodynamic compromise | Lower risk | Higher risk |
| Bleeding | Common in both | Common in both |
| Thrombosis | Risk in both | Risk in both |
Approximately 4% of patients initially placed on VV ECMO require conversion to VA ECMO due to development of hemodynamic instability 1, 4
Implementation Requirements
ECMO should be conducted in centers with sufficient experience, volume, and expertise to ensure it is used safely:
- Rapid implementation (ideally <60 minutes from cardiac arrest for ECPR)
- Multidisciplinary trained team
- Centers with sufficient experience (>20-25 cases/year) to maintain competence
- Comprehensive monitoring including mean arterial pressure, ECMO flow, echocardiography, pulse contour analysis, daily fluid balance, SvO2, and lactate levels 1, 2
Current Evidence and Outcomes
Survival rates with ECMO vary widely depending on the indication:
- As low as 30% in extracorporeal cardiopulmonary resuscitation
- Up to 95% for certain respiratory conditions 5
The quality of evidence for ECMO use in adults remains low to moderate, with significant clinical heterogeneity between studies preventing robust meta-analyses 6
Important Considerations
- ECMO provides life support but is not a form of treatment for the underlying condition
- Anticoagulation is required, which carries risks of bleeding complications
- Technological advances have improved the risk/benefit profile over time
- The decision between VA and VV ECMO should be made by experienced physicians in centers with solid experience in ECMO management 1, 5
ECMO remains a complex, high-risk, and costly modality that should be used judiciously in patients with potentially reversible conditions when conventional therapies have failed.