ECMO Foundations of ECMO and ECMO Management 2 — Questions and Answers
Question 1: Which parameter best reflects the adequacy of oxygen delivery during VV-ECMO?
- SaO2 on the ventilator
- Mixed venous oxygen saturation (SvO2) (Correct answer)
- ECMO pump flow rate
- Recirculation fraction
Correct answer: Mixed venous oxygen saturation (SvO2)
SvO2 reflects the balance between oxygen delivery and consumption, making it the best indicator of systemic oxygen adequacy in VV-ECMO.
Question 2: Recirculation during VV-ECMO is best defined as:
- Retrograde flow from the return cannula to the heart
- Oxygenated blood from the return cannula re-entering the drainage cannula (Correct answer)
- Air entrainment into the ECMO circuit
- Backflow of blood through the oxygenator membrane
Correct answer: Oxygenated blood from the return cannula re-entering the drainage cannula
Recirculation occurs when oxygenated blood exiting the return cannula is immediately aspirated back into the drainage cannula before reaching the systemic circulation.
Question 3: The primary determinant of CO2 removal in the ECMO circuit is:
- Pump blood flow rate
- Sweep gas flow rate (Correct answer)
- FiO2 of the sweep gas
- Membrane lung surface area
Correct answer: Sweep gas flow rate
Sweep gas flow (measured in L/min) is the primary control for CO2 removal; increasing sweep gas flow directly increases CO2 elimination.
Question 4: In VA-ECMO, retrograde aortic flow from a femoral arterial return cannula most significantly affects:
- Renal perfusion pressure
- Left ventricular afterload (Correct answer)
- Circuit oxygenator performance
- Venous drainage adequacy
Correct answer: Left ventricular afterload
Retrograde femoral arterial return increases left ventricular afterload (increased impedance to ejection), which can worsen LV distension in a failing heart.
Question 5: Which cannula configuration is used in veno-arterial-venous (VAV) ECMO?
- Two venous drainage and one arterial return cannula
- One venous drainage, one arterial return, and one additional venous return cannula (Correct answer)
- Two arterial cannulas and one venous cannula
- Dual-lumen cannula in the right atrium only
Correct answer: One venous drainage, one arterial return, and one additional venous return cannula
VAV-ECMO uses one venous drainage cannula with both an arterial and a venous return cannula, providing both cardiac and respiratory support while improving upper body oxygenation.
Question 6: The 'north-south syndrome' (Harlequin syndrome) in VA-ECMO occurs due to:
- ECMO circuit thrombosis obstructing flow
- Recovery of native cardiac function delivering deoxygenated blood to the upper body while ECMO oxygenates the lower body (Correct answer)
- Cannula malposition causing hepatic congestion
- Excessive sweep gas causing severe hypocapnia
Correct answer: Recovery of native cardiac function delivering deoxygenated blood to the upper body while ECMO oxygenates the lower body
Harlequin syndrome occurs when recovering cardiac function ejects deoxygenated blood from the lungs to the upper body, while ECMO oxygenated blood perfuses only the lower body.
Question 7: During ECMO priming, the circuit is typically filled with which solution to remove air before patient connection?
- Heparinized normal saline or balanced crystalloid (Correct answer)
- 5% dextrose water
- Albumin 5% alone
- Fresh frozen plasma
Correct answer: Heparinized normal saline or balanced crystalloid
Heparinized normal saline or balanced crystalloid (e.g., Plasma-Lyte) is the standard prime solution used to displace air and prepare the circuit before connection to the patient.
ECMO Foundations of ECMO and ECMO Management 2
Which parameter best reflects the adequacy of oxygen delivery during VV-ECMO?