VT Dialysis Access Surveillance 2 — Questions and Answers
Question 1: Which Doppler parameter is most commonly used to define hemodynamically significant stenosis in a dialysis AVF?
- Peak systolic velocity ratio >2:1 at stenosis (Correct answer)
- End-diastolic velocity <10 cm/s
- Resistive index >0.7
- Acceleration time >120 ms
Correct answer: Peak systolic velocity ratio >2:1 at stenosis
A peak systolic velocity ratio greater than 2:1 across a stenotic segment indicates hemodynamically significant stenosis in AVF surveillance.
Question 2: A hemodialysis patient's access flow drops from 1,200 mL/min to 550 mL/min over two months. What is the most appropriate next step?
- Continue monitoring at next scheduled interval
- Refer for fistulogram and intervention (Correct answer)
- Increase dialysis session time
- Rotate needle placement sites
Correct answer: Refer for fistulogram and intervention
A >25% decrease in access flow below 500 mL/min warrants urgent referral for fistulogram and possible angioplasty to prevent thrombosis.
Question 3: During duplex surveillance of an AVG, you identify a peak systolic velocity of 450 cm/s within the graft body. The proximal inflow velocity is 120 cm/s. What does this indicate?
- Normal graft hemodynamics
- Inflow stenosis
- Intragraft stenosis with velocity ratio >3:1 (Correct answer)
- Venous hypertension
Correct answer: Intragraft stenosis with velocity ratio >3:1
A velocity ratio of 450/120 = 3.75:1 far exceeds the 2:1 threshold, confirming significant intragraft stenosis.
Question 4: Which finding on duplex ultrasound is most suggestive of venous outflow stenosis in a dialysis AV fistula?
- Elevated brachial artery resistive index
- Pulsatile waveform throughout the fistula (Correct answer)
- Diminished flow volume despite elevated velocities at stenosis
- Subclavian steal phenomenon
Correct answer: Pulsatile waveform throughout the fistula
Outflow stenosis causes increased resistance, converting the normally low-resistance venous waveform to a pulsatile pattern throughout the fistula.
Question 5: What is the recommended minimum access flow threshold below which AVF thrombosis risk is substantially elevated?
- 300 mL/min
- 500 mL/min (Correct answer)
- 750 mL/min
- 1,000 mL/min
Correct answer: 500 mL/min
Access flow below 500 mL/min in an AVF is associated with significantly increased risk of thrombosis and is an intervention threshold.
Question 6: A patient presents with arm swelling and collateral veins on the chest wall. Duplex ultrasound of the access shows markedly elevated cephalic vein velocities. What is the likely diagnosis?
- Steal syndrome
- Central venous stenosis (Correct answer)
- Pseudoaneurysm
- Venous aneurysm
Correct answer: Central venous stenosis
Chest wall collaterals and arm swelling in a dialysis patient indicate central venous stenosis or occlusion, often subclavian or innominate vein.
Question 7: When performing transonic dilution flow measurement during hemodialysis, what does a decrease in ultrasound signal downstream indicate?
- Normal recirculation
- Indicator dilution as saline passes the sensor (Correct answer)
- Air embolism
- Clot formation in the circuit
Correct answer: Indicator dilution as saline passes the sensor
In transonic flow measurement, saline injected upstream causes a transient decrease in ultrasound signal at the downstream sensor used to calculate access blood flow.
VT Dialysis Access Surveillance 2
Which Doppler parameter is most commonly used to define hemodynamically significant stenosis in a dialysis AVF?