ECMO Physiology and Pathophysiology 2

Question 1

During VV-ECMO, a patient's PaO2 remains low despite adequate circuit flow. What is the most likely cause?

Accepted Answer

High recirculation fraction

Answer

High recirculation occurs when oxygenated blood returning from the circuit is immediately re-entrained by the drainage cannula, reducing effective oxygen delivery to the patient.

Question 2

Which hemodynamic effect distinguishes VA-ECMO from VV-ECMO in cardiogenic shock?

Accepted Answer

VA-ECMO provides systemic perfusion pressure support while VV-ECMO does not

Answer

VA-ECMO directly bypasses the heart and lungs, providing mechanical circulatory support and augmenting systemic arterial pressure, whereas VV-ECMO only supports gas exchange.

Question 3

What is the physiological consequence of 'North-South syndrome' (Harlequin syndrome) in femoral VA-ECMO?

Accepted Answer

Upper body receives poorly oxygenated blood from the native failing heart while lower body receives oxygenated ECMO blood

Answer

In femoral VA-ECMO, oxygenated retrograde ECMO flow may not reach the upper body if the recovering heart ejects deoxygenated blood antegrade, creating a watershed zone of hypoxemia in the upper extremities and brain.

Question 4

How does increased ECMO pump speed affect left ventricular (LV) wall stress in VA-ECMO?

Accepted Answer

Increases LV wall stress by increasing afterload via elevated aortic pressure

Answer

Higher VA-ECMO flows increase mean arterial pressure retrograde into the aorta, elevating LV afterload and potentially worsening LV distension if the ventricle cannot eject against the increased pressure.

Question 5

In a patient on VV-ECMO, the sweep gas FiO2 is increased from 0.6 to 1.0 with minimal change in patient PaO2. What does this suggest?

Accepted Answer

Recirculation or inadequate ECMO blood flow relative to cardiac output

Answer

When increasing oxygenator FiO2 has little effect on systemic oxygenation, insufficient ECMO flow relative to native cardiac output means a large fraction of venous blood bypasses the circuit entirely.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Physiology and Pathophysiology 2