Dialysis Access and Preoperative Vascular Mapping
Dialysis Access and Preoperative Vascular Mapping
This domain tests preoperative vein and artery mapping, access surveillance, and interpretation of fistula and graft dysfunction.
Core rules
- Preoperative mapping assesses arterial inflow, venous continuity, and compressibility. A usable cephalic vein is typically ≥2.0-2.5 mm with tourniquet; arterial diameter is usually ≥1.5-2.0 mm. Avoid veins with prior catheters, sclerosis, or ipsilateral subclavian stenosis.
- Access flow (Qa) can be estimated as time-averaged mean velocity × cross-sectional area × 60. A flow <500 mL/min suggests inadequate access and warrants further evaluation.
- Stenosis in a fistula or graft: focal PSV elevation, post-stenotic turbulence, velocity ratio >2:1, or >3:1 in many protocols, and PSV >400 cm/s. Correlate with flow and recirculation.
- Steal syndrome shows retrograde flow in the artery distal to the access; document direction and severity.
Worked example
A brachial artery feeding an AV fistula has flow 350 mL/min. A focal venous outflow PSV is 500 cm/s with a ratio of 4:1 and turbulence. The low flow plus high-grade stenosis indicates access dysfunction and likely referral for fistulography. Check recirculation and arterial inflow before concluding.
Traps
Do not measure flow with a poor angle or assume a normal flow excludes stenosis. Pseudoaneurysm, hematoma, and central vein stenosis can mimic outflow disease. Avoid compressing a newly created access.