ECMO Cannulation Techniques and Strategies 4 — Questions and Answers
Question 1: In venoarterial ECMO, retrograde flow through the femoral artery can cause what phenomenon in patients with recovering cardiac function?
- Pulmonary hypertension
- Differential hypoxia (Harlequin syndrome) (Correct answer)
- Left ventricular thrombus
- Venous air embolism
Correct answer: Differential hypoxia (Harlequin syndrome)
When the recovering heart ejects deoxygenated blood that meets retrograde ECMO flow in the aorta, the upper body may receive hypoxic blood — Harlequin syndrome.
Question 2: What does 'mal-position' of a venous drainage cannula into the hepatic vein most commonly cause?
- Increased ECMO flows
- Decreased venous drainage and 'chattering' (Correct answer)
- Systemic air embolism
- Pulmonary edema
Correct answer: Decreased venous drainage and 'chattering'
Hepatic vein malposition limits drainage volume, causing circuit chattering and inadequate ECMO support.
Question 3: For a patient with bilateral femoral vessel pathology needing VA-ECMO, which alternative arterial site is most commonly used?
- Radial artery
- Axillary or subclavian artery (Correct answer)
- Common carotid artery
- Popliteal artery
Correct answer: Axillary or subclavian artery
The axillary or subclavian artery is the preferred alternative arterial access when femoral vessels are unusable, allowing antegrade cerebral and upper body perfusion.
Question 4: What is the rationale for placing a 'bridge' or purse-string suture around the arterial cannula insertion site during surgical cannulation?
- To maintain cannula position and provide hemostasis upon decannulation (Correct answer)
- To prevent arterial spasm
- To calibrate cannula flow sensors
- To anchor anticoagulation tubing
Correct answer: To maintain cannula position and provide hemostasis upon decannulation
Purse-string sutures secure the cannula, prevent bleeding around it, and facilitate clean hemostasis when the cannula is removed.
Question 5: When using TEE to guide ECMO cannulation, what finding confirms the guidewire is in the correct venous structure rather than the aorta?
- Guidewire echo-brightness is lower in the vein than the aorta
- Guidewire seen in the right atrium or IVC, not the descending aorta (Correct answer)
- Color Doppler shows arterial waveform in the cannulated vessel
- M-mode shows ventricular dilation
Correct answer: Guidewire seen in the right atrium or IVC, not the descending aorta
TEE visualizing the guidewire within the right atrium or IVC confirms venous placement and rules out inadvertent aortic cannulation.
Question 6: In pediatric VA-ECMO, central cannulation via the right atrium and aorta is often preferred over peripheral cannulation because:
- Peripheral vessels are too large for available cannulas
- Central cannulation avoids limb ischemia and allows higher flows in small patients (Correct answer)
- Right atrial cannulation reduces the need for anticoagulation
- Aortic cannulas are smaller than femoral cannulas in children
Correct answer: Central cannulation avoids limb ischemia and allows higher flows in small patients
Small peripheral vessels in children limit flow and increase ischemia risk, making direct central cannulation safer and more effective.
Question 7: Which of the following best describes the 'Y-connector' configuration used in some ECMO venous drainage setups?
- Two return cannulas feeding into one oxygenator
- Two drainage cannulas (femoral + jugular) joined to a single drainage limb to increase flow (Correct answer)
- A connector linking the pump to two oxygenators in parallel
- A pressure-relief valve preventing circuit over-pressurization
Correct answer: Two drainage cannulas (femoral + jugular) joined to a single drainage limb to increase flow
A Y-connector combines drainage from both femoral and jugular veins into a single line, increasing total venous return when one cannula is insufficient.
ECMO Cannulation Techniques and Strategies 4
In venoarterial ECMO, retrograde flow through the femoral artery can cause what phenomenon in patients with recovering cardiac function?