ECMO Physiology and Pathophysiology 4

Question 1

What is the physiological mechanism by which ECMO improves coronary perfusion in cardiogenic shock?

Accepted Answer

VA-ECMO raises aortic diastolic pressure, which is the primary determinant of coronary perfusion pressure

Answer

Coronary perfusion occurs primarily during diastole and depends on aortic diastolic pressure; VA-ECMO's continuous retrograde flow elevates aortic diastolic pressure, improving coronary perfusion pressure.

Question 2

In a patient on peripheral VA-ECMO, which monitoring site best reflects cerebral oxygenation?

Accepted Answer

Right radial arterial blood gas (pre-mixing zone)

Answer

The right radial artery reflects blood ejected from the native heart before it mixes with retrograde ECMO flow, providing the best estimate of oxygen delivery to the brain and coronary arteries.

Question 3

How does systemic inflammatory response syndrome (SIRS) triggered by ECMO circuit contact activation alter vascular physiology?

Accepted Answer

SIRS causes vasodilation and capillary leak, increasing volume requirements and reducing effective circulating volume

Answer

Contact of blood with artificial circuit surfaces activates complement and inflammatory cascades, producing vasodilation and endothelial permeability that manifests as distributive physiology requiring volume resuscitation.

Question 4

What is the physiological basis for using prone positioning concurrently with VV-ECMO in severe ARDS?

Accepted Answer

Prone positioning redistributes ventilation-perfusion matching and reduces dorsal alveolar overdistension, complementing ECMO's gas exchange support

Answer

Prone positioning recruits dorsal lung regions, improves V/Q matching, and reduces cyclic alveolar stress, providing additive benefit to VV-ECMO's extracorporeal gas exchange in ARDS.

Question 5

A patient on VV-ECMO has SvO2 of 85% from the drainage cannula but SpO2 of 82%. What does this pattern indicate?

Accepted Answer

High recirculation: oxygenated blood is being re-drained before reaching the systemic circulation

Answer

When pre-membrane SvO2 (drainage cannula) is nearly as high as or higher than patient SpO2, a large fraction of blood draining into the circuit is already oxygenated, indicating recirculation rather than true mixed venous blood.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Physiology and Pathophysiology 4