ECMO Physiology and Principles 5

Question 1

What is the significance of the 'venous inlet pressure' (P-in) alarm during ECMO, and what does it indicate?

Accepted Answer

Highly negative P-in indicates inadequate venous return, risking cavitation and hemolysis

Answer

A very negative inlet (drainage) pressure indicates hypovolemia, cannula malposition, or kinking, and can cause circuit cavitation, hemolysis, and 'chatter' (intermittent collapse of the venous line).

Question 2

In the context of ECMO physiology, what is 'sweep gas' and what is its primary purpose?

Accepted Answer

A blend of O2 and air passed through the oxygenator to facilitate gas exchange across the membrane

Answer

Sweep gas (typically blended O2 and air) flows through the gas side of the membrane oxygenator, creating the concentration gradient needed for O2 loading and CO2 removal from the blood.

Question 3

Why is systemic anticoagulation required during ECMO, and what is the most common agent used?

Accepted Answer

To prevent circuit thrombosis from blood-surface contact activation; unfractionated heparin is most common

Answer

Blood contact with the artificial circuit surfaces activates the coagulation cascade; unfractionated heparin is the most widely used anticoagulant to prevent life-threatening circuit thrombosis.

Question 4

What is the 'oxygen delivery index' (DO2I) target during ECMO, and why is it important?

Accepted Answer

Approximately 520-600 mL/min/m² to match normal physiologic oxygen demand

Answer

Targeting physiologic DO2I (approximately 520-600 mL/min/m²) ensures adequate tissue oxygenation while avoiding excessive flow that could increase hemolysis and recirculation.

Question 5

How does the position of the return (reinfusion) cannula relative to the drainage cannula affect recirculation in single-access dual-lumen VV-ECMO?

Accepted Answer

The return jet must be directed toward the tricuspid valve to minimize recirculation

Answer

In dual-lumen cannulas (e.g., Avalon), proper positioning directs the return jet toward the tricuspid valve, propelling oxygenated blood into the right ventricle rather than back toward the drainage holes.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Physiology and Principles 5