What does a 90% Extracorporeal Membrane Oxygenation (ECMO) flow indicate?

Interpretation of 90% ECMO Flow

90% ECMO flow indicates that the ECMO circuit is providing 90% of the patient's total cardiac output, meaning the native heart is contributing only 10% of systemic perfusion—a state of profound cardiac failure with critical implications for organ perfusion patterns and mixing point location.

Understanding ECMO Flow Percentage

Flow percentage represents the proportion of total systemic circulation provided by the ECMO pump versus the native heart. 1

• In VA-ECMO, when ECMO provides 90% or more of total flow, this indicates near-complete circulatory support with minimal native cardiac function 1
• The remaining 10% represents antegrade flow from the failing left ventricle 1
• This degree of support is typically seen in profound cardiogenic shock requiring maximal mechanical circulatory support 2

Critical Hemodynamic Implications

At 90% ECMO flow, the watershed (mixing point) region is positioned in the aortic arch, creating a high-risk scenario for differential hypoxemia. 1

• The collision point between retrograde ECMO flow and minimal antegrade cardiac flow occurs proximally in the aortic arch 1
• Minimal pulsatility is observed in flow to visceral organs at this level of support 1
• The upper body (brain and coronary arteries) may receive poorly oxygenated blood from the failing native lungs if the mixing point is distal 3

Monitoring Requirements at 90% Flow

Right radial arterial blood gas sampling is essential to assess cerebral oxygenation, as this site best represents what the brain receives. 3

• Pulse pressure assessment from the right radial line provides real-time indication of mixing point location 3
• A wide pulse pressure indicates significant left ventricular ejection reaching the upper body, suggesting a distal mixing point 3
• Continuous monitoring of arterial blood pressure and ECMO flow is mandatory 4
• Repeated echocardiography is essential to assess native cardiac function 4

Clinical Significance and Management

At 90% ECMO support, the patient is in a state of near-complete cardiac failure requiring aggressive monitoring for differential hypoxemia. 1

• This level of support indicates the heart is providing minimal contribution to systemic perfusion 1
• Immediate intervention is required if upper body hypoxemia develops, including increasing ECMO flow to move the mixing point proximally 3
• Optimizing mechanical ventilation to improve native lung oxygenation reduces the oxygen gradient between competing circulations 3
• Consider V-AV ECMO configuration (adding jugular venous return cannula) if differential hypoxemia persists despite maximal interventions 3

Prognostic Considerations

Such profound dependence on ECMO support (90% flow) reflects critical illness with modest survival rates. 2

• Adult ECMO survival rates range from 24-58% depending on indication and duration 2
• Outcomes improve when ECMO is used for specific reversible conditions like acute myocarditis (75% adult survival) 2
• This level of support should only be provided at high-volume centers (>20-25 cases annually) with multidisciplinary expertise 4

Common Pitfalls

• Failing to obtain right radial arterial blood gases can miss critical upper body hypoxemia when the mixing point is distal 3
• Relying on lower extremity oxygen saturation does not reflect cerebral or coronary perfusion at high ECMO flows 3
• Inadequate assessment of native cardiac recovery may delay appropriate weaning strategies or escalation to durable support 4