ECMO Circuit Components and Management 2 — Questions and Answers
Question 1: What is the primary purpose of the raceway tubing in a centrifugal ECMO pump?
- To serve as the segment compressed by the pump head (Correct answer)
- To oxygenate blood passing through the circuit
- To house the heat exchanger coils
- To measure circuit flow via ultrasonic sensors
Correct answer: To serve as the segment compressed by the pump head
Raceway tubing is the specialized, crush-resistant segment that sits within a roller pump head and is repeatedly compressed to propel blood.
Question 2: Which ECMO circuit component is responsible for removing CO2 from the patient's blood?
- Centrifugal pump
- Oxygenator membrane (Correct answer)
- Bladder reservoir
- Servo-regulation sensor
Correct answer: Oxygenator membrane
The oxygenator membrane facilitates both oxygen delivery and CO2 removal via diffusion across hollow fiber membranes.
Question 3: When a 'chatter' or 'flutter' is observed in the venous drainage tubing, the most likely cause is:
- Excessive pump flow rate relative to venous return (Correct answer)
- Air embolism in the arterial limb
- Membrane lung thrombosis
- Heat exchanger malfunction
Correct answer: Excessive pump flow rate relative to venous return
Tubing chatter indicates inadequate venous return relative to the pump's demand, causing intermittent collapse and re-expansion of the drainage line.
Question 4: The sweep gas flow rate in ECMO primarily controls which parameter?
- Patient oxygenation
- CO2 removal (Correct answer)
- Circuit blood flow
- Patient temperature
Correct answer: CO2 removal
Sweep gas flow (the gas flowing through the oxygenator fiber lumen) is the primary determinant of CO2 clearance from the blood.
Question 5: What is the recommended strategy when air is detected in the ECMO circuit?
- Clamp the circuit, stop the pump, and remove air before restarting (Correct answer)
- Increase pump speed to push air through quickly
- Administer IV heparin bolus immediately
- Switch from VA to VV ECMO mode
Correct answer: Clamp the circuit, stop the pump, and remove air before restarting
Air entry requires immediate circuit clamping and pump stoppage to prevent air embolism, followed by controlled de-airing before circuit restart.
Question 6: The 'recirculation' phenomenon in VV-ECMO occurs when:
- Oxygenated blood returning to the patient is re-entrained into the drainage cannula (Correct answer)
- The pump spins in reverse direction
- CO2 accumulates in the oxygenator fiber bundle
- The heat exchanger overheats the blood
Correct answer: Oxygenated blood returning to the patient is re-entrained into the drainage cannula
Recirculation in VV-ECMO occurs when returned oxygenated blood is immediately suctioned back into the drainage cannula instead of circulating through the patient.
Question 7: Which cannula configuration is used in VV-ECMO with a single dual-lumen cannula?
- Bicaval dual-lumen cannula inserted via the internal jugular vein (Correct answer)
- Femoral artery to femoral vein
- Right atrium to ascending aorta
- Pulmonary artery to left atrium
Correct answer: Bicaval dual-lumen cannula inserted via the internal jugular vein
The Avalon or similar bicaval dual-lumen cannulas are placed via the right internal jugular vein, with drainage from both caval veins and return to the right atrium.
