ECMO Veno-Venous (VV) ECMO Management 2

Question 1

A patient on VV ECMO has a pre-membrane pO2 of 35 mmHg and post-membrane pO2 of 450 mmHg, yet SpO2 remains at 78%. What is the most likely cause?

Accepted Answer

High recirculation fraction

Answer

High recirculation returns already-oxygenated blood back to the drainage cannula, reducing effective oxygen delivery despite excellent oxygenator function.

Question 2

Which intervention most directly reduces recirculation in a patient on dual-lumen bicaval VV ECMO?

Accepted Answer

Repositioning the return jet away from the drainage port

Answer

Directing the return jet toward the tricuspid valve and away from the drainage port minimizes recirculation of oxygenated blood.

Question 3

On VV ECMO, a patient's SaO2 is 88% with ECMO flow at 5 L/min. The native cardiac output is estimated at 8 L/min. What is the approximate recirculation fraction?

Accepted Answer

37%

Answer

Recirculation fraction = (ECMO flow – effective flow) / ECMO flow; with total venous return mixed with ECMO flow, approximately 37% recirculation yields this oxygen delivery.

Question 4

Which blood gas parameter is MOST useful to assess oxygenator function independent of recirculation on VV ECMO?

Accepted Answer

Post-membrane pO2

Answer

Post-membrane pO2 directly reflects the oxygenator's gas exchange efficiency regardless of recirculation or native cardiac function.

Question 5

A VV ECMO patient develops sudden increase in transmembrane pressure gradient from 20 to 80 mmHg over 6 hours. What is the most likely cause?

Accepted Answer

Thrombosis within the oxygenator

Answer

Progressive clot formation within the oxygenator increases resistance to blood flow, causing the transmembrane pressure gradient to rise.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Veno-Venous (VV) ECMO Management 2