What does an Extracorporeal Membrane Oxygenation (ECMO) flow of 60% indicate?

ECMO Flow at 60%: Clinical Significance and Management

ECMO flow at 60% means the ECMO circuit is providing 60% of the patient's total cardiac output, with the native heart contributing the remaining 40% of systemic perfusion. 1, 2

Hemodynamic Interpretation

When ECMO flow-to-cardiac output ratio reaches 60%, this represents a critical threshold where adequate arterial oxygenation (SaO2 >90%) is consistently maintained. 2 This level indicates:

• The patient has significant but not complete cardiac failure, requiring substantial mechanical circulatory support 1
• The native heart retains meaningful contractile function (40% contribution), which is prognostically favorable compared to higher ECMO dependency 2
• Blood oxygenation becomes reliably adequate at this flow ratio, as demonstrated in ARDS patients where ECMO flow/cardiac output >60% was constantly associated with appropriate oxygen saturation 2

Risk of Differential Hypoxemia (Harlequin Syndrome)

At 60% ECMO flow, the mixing point of oxygenated retrograde ECMO blood and potentially poorly-oxygenated antegrade left ventricular blood becomes clinically relevant 3:

• The mixing zone location is unstable at this flow level, moving approximately 5cm between systole and diastole throughout the cardiac cycle 3
• This creates risk for intermittent upper body (cerebral and coronary) hypoxemia if native lung function is severely impaired 4, 1
• The mixing point has not yet moved proximally enough to consistently protect cerebral circulation, unlike flows >70% where the mixing zone stabilizes in the aortic arch 3

Essential Monitoring Requirements

Right radial arterial blood gas sampling is mandatory to assess cerebral oxygenation, as this site best represents what the brain and coronary arteries receive. 4, 1 Specific monitoring includes:

• Continuous pulse pressure assessment from the right radial arterial line provides real-time indication of mixing point location 4
• Narrow pulse pressure suggests mixing proximal to the innominate artery (better cerebral protection), while wide pulse pressure indicates more distal mixing with greater risk of upper body hypoxemia 4
• Arteriovenous O2 difference should be maintained between 3-5 cc O2/100ml blood, as this parameter is not influenced by hemoglobin levels 4
• Mixed venous saturation (SvO2) goal >66%, though this is hemoglobin-dependent and less reliable 4

Management Strategy at 60% Flow

After ECMO flows are optimized and the patient is hemodynamically stable, strive for daily negative fluid balance, but if this impacts ECMO flows, fluids remain indicated. 4 Key management principles include:

• Maintain mean arterial pressure that provides adequate cerebral and end-organ perfusion while minimizing left ventricular afterload 4
• Wean vasoactive inotropic support as tolerated to reduce myocardial oxygen demand 4
• If upper body hypoxemia develops despite 60% flow, immediately increase ECMO flow to move the mixing point proximally 4, 1
• Optimize mechanical ventilation settings to improve native lung oxygenation and reduce the oxygen gradient between competing circulations 4, 1

Clinical Pitfalls to Avoid

Do not rely solely on lower extremity arterial blood gas measurements, as these may be falsely reassuring while the brain receives poorly oxygenated blood. 4, 1 Additional cautions:

• Positive fluid balance by the third day of ECMO is associated with increased mortality, so aggressive fluid management is critical once hemodynamically stable 4
• At 60% flow, the patient remains at risk for complications occurring in up to 60% of ECPR cases, which significantly impact survival 4
• Consider V-AV ECMO configuration (adding jugular venous return cannula) if differential hypoxemia persists despite flow optimization and ventilator adjustments 4, 1

Prognostic Considerations

This level of support should only be provided at high-volume centers (>20-25 cases annually) with multidisciplinary expertise, as outcomes are significantly better at experienced centers. 1, 5 The 60% flow level suggests:

• Potential for cardiac recovery given retained native function, which is more favorable than near-complete ECMO dependency 1, 2
• Need for repeated echocardiography to assess native cardiac function and guide weaning strategies 1
• Consideration of transition pathways to durable ventricular assist devices or transplantation if recovery does not occur 5