ECMO Cannulation Techniques and Strategies 2 — Questions and Answers
Question 1: During femoral veno-arterial ECMO cannulation, what is the primary concern when selecting the arterial cannula size?
- Maximizing flow while minimizing distal limb ischemia risk (Correct answer)
- Ensuring the cannula reaches the ascending aorta
- Matching cannula diameter to the patient's body weight only
- Selecting the largest cannula to reduce resistance
Correct answer: Maximizing flow while minimizing distal limb ischemia risk
Femoral arterial cannula selection balances adequate ECMO flow with preservation of native limb perfusion to prevent distal ischemia.
Question 2: What is the purpose of a distal perfusion cannula (DPC) in femoral VA-ECMO?
- To increase venous drainage
- To prevent ipsilateral lower limb ischemia (Correct answer)
- To measure pulmonary artery pressures
- To improve oxygenator performance
Correct answer: To prevent ipsilateral lower limb ischemia
A DPC is placed in the superficial femoral artery to perfuse the limb distal to the ECMO arterial cannula, preventing ischemia.
Question 3: Which ultrasound view is most useful for confirming guidewire position in the inferior vena cava during femoral venous cannulation?
- Parasternal long-axis
- Subcostal or transesophageal bicaval view (Correct answer)
- Apical four-chamber
- Parasternal short-axis at the aortic valve
Correct answer: Subcostal or transesophageal bicaval view
The subcostal or TEE bicaval view provides direct visualization of the guidewire and cannula tip within the IVC and right atrium.
Question 4: In percutaneous cannulation, serial dilation of the vessel is performed to:
- Increase anticoagulation effect
- Gradually expand the access site to accommodate the final cannula (Correct answer)
- Flush the cannula with heparin solution
- Test vessel compliance before ECMO initiation
Correct answer: Gradually expand the access site to accommodate the final cannula
Sequential dilators progressively enlarge the puncture site so the large-bore ECMO cannula can be inserted without tearing the vessel.
Question 5: When transitioning from peripheral VA-ECMO to central cannulation, what is the main hemodynamic advantage?
- Lower systemic anticoagulation requirements
- Elimination of differential hypoxia by delivering oxygenated blood centrally (Correct answer)
- Reduced risk of air embolism
- Improved venous drainage from the femoral vein
Correct answer: Elimination of differential hypoxia by delivering oxygenated blood centrally
Central aortic return eliminates the mixing zone issue seen in peripheral VA-ECMO, preventing differential (Harlequin) hypoxia.
Question 6: What landmark is used to estimate the optimal venous cannula tip position in the right atrium during fluoroscopic-guided femoral VV-ECMO cannulation?
- The level of the diaphragm
- The carina or right mainstem bronchus at the cavoatrial junction (Correct answer)
- The left hilum
- The aortic knob
Correct answer: The carina or right mainstem bronchus at the cavoatrial junction
Fluoroscopically, the cavoatrial junction correlates with the level of the carina, guiding optimal venous drainage cannula tip placement.
Question 7: Which complication is most specifically associated with axillary artery cannulation for VA-ECMO compared to femoral artery cannulation?
- Distal leg ischemia
- Brachial plexus injury (Correct answer)
- Aortic dissection
- Retroperitoneal hematoma
Correct answer: Brachial plexus injury
The brachial plexus lies adjacent to the axillary artery, making nerve injury a specific risk of this cannulation approach.
ECMO Cannulation Techniques and Strategies 2
During femoral veno-arterial ECMO cannulation, what is the primary concern when selecting the arterial cannula size?