CES ECMO Physiology & Gas Exchange 1 — Questions and Answers
Question 1: In peripheral veno-arterial (VA) ECMO, the venous drainage cannula is typically placed in which vessel?
- Femoral artery
- Femoral vein (Correct answer)
- Subclavian vein
- Internal jugular vein
Correct answer: Femoral vein
In peripheral VA-ECMO, blood is drained from the femoral vein and returned via the femoral artery, bypassing the heart and lungs.
Question 2: The primary function of increasing sweep gas flow in a membrane oxygenator is to:
- Increase blood flow through the circuit
- Control the temperature of circulating blood
- Remove carbon dioxide from the blood (Correct answer)
- Prevent thrombus formation in the membrane
Correct answer: Remove carbon dioxide from the blood
Sweep gas flow across the membrane lung primarily drives CO2 removal by creating a diffusion gradient that eliminates CO2 from the blood.
Question 3: In veno-venous (VV) ECMO, the primary physiologic goal is to:
- Provide mechanical cardiac support
- Support gas exchange while maintaining native cardiac function (Correct answer)
- Reduce pulmonary vascular resistance directly
- Increase systemic vascular resistance
Correct answer: Support gas exchange while maintaining native cardiac function
VV-ECMO supports oxygenation and CO2 removal in patients with respiratory failure while relying on the native heart to maintain cardiac output.
Question 4: Recirculation in VV-ECMO refers to which of the following phenomena?
- Blood flowing backward through the pump head
- Oxygenated return blood being immediately re-drained into the circuit before reaching the patient (Correct answer)
- Air entrainment on the venous side of the circuit
- Clot formation causing retrograde flow in the oxygenator
Correct answer: Oxygenated return blood being immediately re-drained into the circuit before reaching the patient
Recirculation occurs when oxygenated blood exiting the return cannula is pulled back into the drainage cannula, reducing effective ECMO support.
Question 5: In a patient on VA-ECMO, mixed venous oxygen saturation (SvO2) primarily reflects:
- The function of the membrane oxygenator
- The patient's native pulmonary function
- The balance between systemic oxygen delivery and consumption (Correct answer)
- The degree of systemic anticoagulation
Correct answer: The balance between systemic oxygen delivery and consumption
SvO2 represents the oxygen remaining after tissues extract what they need; a low SvO2 signals that DO2 is insufficient relative to VO2.
Question 6: Oxygen delivery (DO2) in an ECMO patient is calculated using which of the following components?
- ECMO flow rate multiplied by sweep gas FiO2
- Cardiac output multiplied by arterial oxygen content (CaO2) (Correct answer)
- Pump speed (RPM) multiplied by hemoglobin concentration
- Post-oxygenator PO2 multiplied by blood flow rate
Correct answer: Cardiac output multiplied by arterial oxygen content (CaO2)
DO2 = Cardiac output (native + ECMO) × CaO2; CaO2 includes hemoglobin-bound and dissolved oxygen.
Question 7: In VA-ECMO, increasing pump flow rate will primarily have which effect?
- Increase arterial PaCO2 by reducing membrane dwell time
- Decrease venous return to the native heart, reducing native cardiac preload (Correct answer)
- Increase afterload on the left ventricle
- Increase mixed venous oxygen saturation by reducing recirculation
Correct answer: Decrease venous return to the native heart, reducing native cardiac preload
Higher VA-ECMO flows drain more blood from the venous side, reducing preload to the right heart and diminishing native cardiac output.
CES ECMO Physiology & Gas Exchange 1
In peripheral veno-arterial (VA) ECMO, the venous drainage cannula is typically placed in which vessel?