ECMO Veno-Venous (VV) ECMO Management 2 — Questions and Answers
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?
- Membrane oxygenator failure
- High recirculation fraction (Correct answer)
- Inadequate ECMO blood flow
- Venous air embolism
Correct answer: High recirculation fraction
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?
- Increasing sweep gas flow
- Repositioning the return jet away from the drainage port (Correct answer)
- Increasing anticoagulation
- Raising ECMO blood flow
Correct answer: Repositioning the return jet away from the drainage port
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?
- 10%
- 25%
- 37% (Correct answer)
- 50%
Correct answer: 37%
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?
- Pre-membrane arterial blood gas
- Post-membrane pO2 (Correct answer)
- Mixed venous saturation from a Swan-Ganz catheter
- Peripheral SpO2
Correct answer: Post-membrane pO2
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?
- Kinking of the drainage cannula
- Thrombosis within the oxygenator (Correct answer)
- Increased cardiac output
- Hypovolemia
Correct answer: Thrombosis within the oxygenator
Progressive clot formation within the oxygenator increases resistance to blood flow, causing the transmembrane pressure gradient to rise.
Question 6: During VV ECMO, the sweep gas FiO2 is increased from 0.6 to 1.0 but CO2 remains elevated. What adjustment should be made?
- Increase ECMO blood flow
- Increase sweep gas flow rate (Correct answer)
- Decrease ECMO blood flow
- Switch to VA ECMO
Correct answer: Increase sweep gas flow rate
CO2 removal on ECMO is primarily determined by sweep gas flow rate (not FiO2), so increasing sweep gas flow enhances CO2 elimination.
Question 7: Which patient position is generally preferred during VV ECMO to optimize oxygenation in refractory ARDS?
- Supine with head of bed at 30°
- Prone positioning (Correct answer)
- Lateral decubitus on the right side
- Trendelenburg
Correct answer: Prone positioning
Prone positioning improves V/Q matching and recruits dorsal lung regions, complementing VV ECMO support in refractory ARDS.
ECMO Veno-Venous (VV) ECMO Management 2
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?