ECMO Cannulation Techniques and Strategies 5 — Questions and Answers
Question 1: What is the most significant risk of advancing the venous drainage cannula too far into the right ventricle during ECMO cannulation?
- Improved drainage due to proximity to the tricuspid valve
- Ventricular arrhythmias and potential perforation (Correct answer)
- Increased recirculation in VV-ECMO
- Air entrainment from the pulmonary veins
Correct answer: Ventricular arrhythmias and potential perforation
A cannula tip in the right ventricle can irritate the myocardium, trigger ventricular arrhythmias, and risk perforation of the thin RV wall.
Question 2: During emergent bedside percutaneous ECMO cannulation without fluoroscopy, which bedside imaging tool is considered the standard of care for real-time guidance?
- Computed tomography angiography
- Point-of-care ultrasound (POCUS) (Correct answer)
- Magnetic resonance imaging
- Nuclear perfusion scanning
Correct answer: Point-of-care ultrasound (POCUS)
POCUS enables real-time vessel visualization, needle guidance, and cannula tip confirmation at the bedside without radiation or contrast.
Question 3: Which characteristic of a wire-reinforced ECMO cannula reduces the risk of circuit failure?
- The wire coating increases biocompatibility
- The reinforcement prevents kinking under bending or positional changes (Correct answer)
- Wire reinforcement increases cannula rigidity to prevent malposition
- The wire increases electrical conductivity for flow sensing
Correct answer: The reinforcement prevents kinking under bending or positional changes
Wire reinforcement maintains cannula lumen patency under compression or bending, preventing flow interruption from kinking.
Question 4: A patient on femoral VA-ECMO develops sudden loss of ECMO flow with high negative inlet pressures and circuit chattering. After ruling out hypovolemia, the next step is to:
- Increase pump speed to overcome the resistance
- Assess for suction events by repositioning or flushing the drainage cannula (Correct answer)
- Switch to a higher-flow oxygenator
- Administer vasopressors to increase preload
Correct answer: Assess for suction events by repositioning or flushing the drainage cannula
Persistent chattering after correcting volume suggests the drainage cannula is against a vessel wall; repositioning or minor flushing can relieve obstruction.
Question 5: What is the primary advantage of a percutaneous over a surgical cutdown approach for ECMO cannulation in most adults?
- Larger cannulas can be placed percutaneously
- Faster access, lower bleeding risk at the site, and no surgical wound (Correct answer)
- Surgical cutdown provides worse visualization of vessel anatomy
- Percutaneous cannulas are easier to remove at decannulation
Correct answer: Faster access, lower bleeding risk at the site, and no surgical wound
Percutaneous Seldinger-based cannulation is faster in an emergency, avoids a surgical incision, and is associated with lower local complication rates in experienced hands.
Question 6: In VV-ECMO using a bicaval dual-lumen cannula, what is the consequence of clockwise rotation of the cannula when the return port faces posteriorly instead of toward the tricuspid valve?
- Increased drainage efficiency
- Increased recirculation as oxygenated blood re-enters the drainage lumen (Correct answer)
- Aortic injury from the tip
- Left ventricular unloading
Correct answer: Increased recirculation as oxygenated blood re-enters the drainage lumen
Posterior misdirection of the return port allows oxygenated blood to recirculate back into the drainage lumen rather than crossing the tricuspid valve into the pulmonary circuit.
Question 7: What is the primary purpose of performing an 'Allen test' or Doppler assessment of palmar arch collaterals before radial artery cannulation used as a monitoring line during ECMO?
- To measure systemic vascular resistance
- To ensure adequate collateral flow if the radial artery becomes occluded (Correct answer)
- To confirm absence of arteriovenous fistula
- To assess cardiac output by pulse contour analysis
Correct answer: To ensure adequate collateral flow if the radial artery becomes occluded
Confirming intact ulnar collateral circulation ensures hand perfusion is maintained even if the radial artery is compromised by the monitoring cannula.
ECMO Cannulation Techniques and Strategies 5
What is the most significant risk of advancing the venous drainage cannula too far into the right ventricle during ECMO cannulation?