VABC Ultrasound Guidance 3 — Questions and Answers
Question 1: Which ultrasound finding confirms that a catheter tip is positioned in the superior vena cava rather than the right atrium?
- Absence of respiratory phasicity in the waveform
- Lack of visible catheter on short-axis view
- Catheter tip visualized above the cavoatrial junction with confirmatory chest X-ray or intracavitary ECG (Correct answer)
- Color Doppler showing retrograde flow
Correct answer: Catheter tip visualized above the cavoatrial junction with confirmatory chest X-ray or intracavitary ECG
Optimal catheter tip position in the SVC is confirmed by locating it above the cavoatrial junction, typically verified with chest X-ray or intracavitary ECG changes.
Question 2: What is the recommended frequency range for linear transducers used in peripheral vascular access ultrasound guidance?
- 1–5 MHz
- 5–10 MHz
- 7–15 MHz (Correct answer)
- 20–30 MHz
Correct answer: 7–15 MHz
Linear transducers in the 7–15 MHz range provide optimal resolution for superficial vascular structures during peripheral vascular access.
Question 3: During ultrasound-guided femoral vein cannulation, the femoral artery is typically located in relation to the femoral vein as:
- Medial
- Lateral (Correct answer)
- Posterior
- Superficial
Correct answer: Lateral
In the femoral triangle, the femoral artery lies lateral to the femoral vein (mnemonic: NAVEL — Nerve, Artery, Vein, Empty space, Lymphatics, lateral to medial).
Question 4: When performing ultrasound-guided subclavian/axillary vein access, which view reduces the risk of pneumothorax compared to the traditional landmark approach?
- Supraclavicular short-axis view
- Infraclavicular long-axis view targeting the axillary vein (Correct answer)
- Parasternal view with probe over the clavicle
- Subcostal approach with steep needle angle
Correct answer: Infraclavicular long-axis view targeting the axillary vein
The infraclavicular long-axis approach targeting the axillary vein allows real-time needle visualization and keeps the needle path away from the pleura, reducing pneumothorax risk.
Question 5: What does a 'double lumen' sign on ultrasound indicate during central line placement?
- Successful venous cannulation confirmed
- The guidewire has passed into a second vessel (Correct answer)
- Air embolism within the target vessel
- The catheter has split into two lumens within the vein
Correct answer: The guidewire has passed into a second vessel
The 'double lumen' sign occurs when the guidewire is visualized in a vessel adjacent to the intended target, indicating extraluminal or wrong-vessel wire placement.
Question 6: Which of the following best describes the 'out-of-plane' needle technique in ultrasound-guided vascular access?
- The needle travels parallel to the ultrasound beam throughout insertion
- The needle crosses the ultrasound beam perpendicularly so only a cross-section (dot) is seen (Correct answer)
- The probe is rotated to follow the needle's path continuously
- The needle is inserted without ultrasound visualization to the vessel
Correct answer: The needle crosses the ultrasound beam perpendicularly so only a cross-section (dot) is seen
In the out-of-plane technique, the needle crosses the ultrasound plane at 90 degrees, appearing as a bright dot on the image rather than as a line.
Question 7: Increased echogenicity (brightness) within a vein lumen on B-mode ultrasound most likely represents:
- Normal laminar blood flow
- Thrombus formation (Correct answer)
- Calcification of the venous wall
- An artifact from adjacent bone
Correct answer: Thrombus formation
Echogenic material within a vein lumen is highly suggestive of thrombus, which should prompt reassessment of the access site.
VABC Ultrasound Guidance 3
Which ultrasound finding confirms that a catheter tip is positioned in the superior vena cava rather than the right atrium?