Vein mapping ultrasound before AV fistula surgery: protocol and criteria
Before an arteriovenous fistula is created, ultrasound shows which arteries and veins are usable, where the anastomosis should go and what problems need solving first. This guide covers who should be mapped, what to measure in the arteries, the veins and the central veins, which minimum diameters are used and what the report should include.
Key points
- Everyone or selected patients? The Spanish GEMAV guideline proposes routine preoperative ultrasound [1]. KDOQI 2019 reserves it for patients at high risk of access failure, such as previous central venous stenosis or an inconclusive physical exam [2].
- The evidence favors routine mapping. In a randomized trial, routine mapping improved fistula patency and use; 12 patients had to be mapped to prevent one failure [4]. In a meta-analysis of 18 studies it reduced primary failure (risk ratio 0.56; low certainty) [5].
- Classic criteria: artery of 2 mm or more; vein of 2.5 mm or more for a native fistula and 4 mm or more for a graft, with a patent palmar arch [3]. The European ESVS guideline gives a minimum of 2 mm in the forearm and 3 mm in the upper arm [6].
- Do not forget the central veins. A subclavian waveform without respiratory variation or cardiac pulsatility suggests central stenosis, which is common after central venous catheters [7].
- Mapping is a plan. It should end in a concrete proposal (which fistula and where) and a drawing that will also guide the first cannulations.
Map everyone, or only some patients?
Guidelines disagree. The Spanish GEMAV guideline proposes routine preoperative ultrasound evaluation [1]. KDOQI 2019 changed the 2006 recommendation (map everyone) to a selective one: ultrasound for patients at high risk of access failure, for example with previous central venous stenosis or when the physical exam gives little information [2].
More recent data tip the balance toward routine mapping:
- In Ferring's trial, adding routine ultrasound to clinical assessment improved fistula patency and use for dialysis. Twelve patients had to be mapped to prevent one fistula failure [4].
- In a 2024 meta-analysis (18 studies, 3,655 participants), routine mapping was associated with less primary fistula failure (risk ratio 0.56; low certainty) and higher 1-year primary patency (risk ratio 1.33; moderate certainty) [5].
Mapping also leaves something the physical exam does not: comparable measurements for follow-up and a drawing of the arm that the dialysis team will use months later.
Before you start
- A high-frequency linear probe with color and pulsed-wave Doppler.
- Patient seated or supine, arm supported and abducted, in a warm room: cold constricts veins and makes them look smaller.
- Map both arms, starting with the non-dominant one.
- Minimal probe pressure and plenty of gel. Superficial veins flatten with very little pressure.
- Ask and examine first: previous central catheters or pacemakers, repeated IVs and blood draws, earlier accesses, edema and blood pressure difference between the arms.
Arterial protocol
| Where | What to measure or check |
|---|---|
| Brachial artery, above the elbow | Inner diameter, waveform (normally triphasic, high resistance), peak systolic velocity and calcification. Look for a high bifurcation: the radial artery can arise in the upper arm. |
| Radial artery at the wrist | Inner diameter (inner wall to inner wall), wall calcification, stenosis and flow to the hand. |
| Ulnar artery | Patency and flow: it supplies the hand if the radial artery is used. |
| Palmar arch | Patent (Doppler or Allen test) [3]. |
| Both arms | Blood pressure difference between the arms: a gradient suggests a proximal stenosis [3]. |
A heavily calcified wall looks like a rail track with acoustic shadowing. Such an artery is stiffer and dilates less after the anastomosis; record it even if the diameter is adequate.
Venous protocol
Veins are measured with a tourniquet placed proximal to the segment studied, because how much the vein dilates when return is occluded indicates how much it can grow after surgery.
| Vein | What to measure or check |
|---|---|
| Cephalic, wrist to shoulder | Inner diameter at several levels (wrist, mid-forearm, elbow, upper arm), depth, continuity and straight segments. |
| Basilic | Diameter and continuity in the forearm and the upper arm, where it runs deep: the candidate for a transposition. |
| Elbow veins (median, perforating) | Diameter and communication with the deep veins: alternatives for an elbow fistula. |
| All | Full compressibility (no thrombus or sclerosis from previous punctures), branches that may steal flow and segmental stenoses. |
| Outflow veins for a graft | Diameter of 4 mm or more [3]. |
Also record depth: a vein that matures more than 6 mm below the skin will be hard to cannulate and may need superficialization (see the rule of 6s).
Central veins
A fistula with a good anastomosis fails if central outflow is stenosed. With the patient supine, assess the subclavian, axillary and internal jugular veins with Doppler. The normal waveform shows respiratory variation and transmitted cardiac pulsatility. If these are lost, or the waveform is flat and continuous, suspect a central stenosis [7]. Ultrasound sees the segment behind the clavicle poorly, so after previous catheters or with an abnormal waveform the team may request venography.
Minimum diameter criteria
| Source | Artery | Vein | Comment |
|---|---|---|---|
| Silva 1998 [3] | ≥ 2.0 mm | ≥ 2.5 mm for a native fistula; ≥ 4.0 mm for a graft | With a patent palmar arch and no pressure gradient between the arms. The most widely cited criteria. |
| ESVS 2018 [6] | ≥ 2 mm in the forearm; ≥ 3 mm in the upper arm | For artery and vein | |
| GEMAV 2017 [1] | No single minimum | In the data it cites, veins under 2 mm were associated with less radiocephalic fistula success; borderline cases are discussed with surgery | |
Diameters are a guide. A large but heavily calcified artery, or a wide vein with a thrombosed segment, can be worse options than slightly smaller, healthy vessels.
From map to decision
Mapping has to end in a proposal: the most distal fistula possible with suitable vessels, in the non-dominant arm if possible, plus an alternative if the first option fails (see types of AV fistula). A good report includes:
- arterial and venous diameters at each level, with and without a tourniquet;
- depth of the candidate veins;
- calcification, stenoses, thrombi and anatomical variants, such as a high brachial bifurcation;
- the state of the central veins;
- a drawing of the arm with the course of the usable veins;
- the proposal: type of fistula, side and level, and the alternative.
The same drawing helps months later to plan the first cannulations. And from the day of mapping, the chosen arm should be protected: no IVs or blood draws in its veins (see ultrasound-guided peripheral IV and vein preservation).
Common mistakes
- Measuring the vein without a tourniquet, or with the probe pressing: the diameter comes out smaller than it is.
- Measuring outer wall to outer wall instead of the inner diameter.
- Mapping in a cold room or with a vasoconstricted patient.
- Forgetting the central veins in a patient with previous catheters.
- Missing a high brachial bifurcation or radial artery calcification.
- Leaving no drawing: loose measurements do not help the surgeon or the person who will cannulate.
Frequently asked questions
What is vein mapping before a fistula?
A Doppler ultrasound of the arm arteries and veins, and of the central veins, to decide which fistula to create and where. It measures diameters, depth and flow, and looks for calcification, thrombi, stenoses and anatomical variants.
What is the minimum vein diameter for an AV fistula?
The most widely cited criteria require a vein of 2.5 mm or more, measured with a tourniquet, for a native fistula, and 4 mm or more for a graft. The European ESVS guideline gives a minimum of 2 mm in the forearm and 3 mm in the upper arm. These are guides: borderline cases are reviewed with the surgical team.
What is the minimum artery diameter?
Usually 2 mm or more, with no major wall calcification and a patent palmar arch. In the upper arm, ESVS gives a minimum of 3 mm.
Should every patient have vein mapping?
GEMAV proposes it routinely and KDOQI 2019 reserves it for high-risk patients. A randomized trial and a recent meta-analysis found fewer fistula failures with routine mapping, with low to moderate certainty.
Why is the vein measured with a tourniquet?
Because how much the vein dilates when return is occluded reflects its ability to grow once it receives arterial flow. Measured without a tourniquet, a usable vein can look too small.
How are central veins assessed with ultrasound?
With Doppler of the subclavian, axillary and internal jugular veins, with the patient supine. A waveform without respiratory variation or cardiac pulsatility suggests central stenosis. Ultrasound sees the segment behind the clavicle poorly, and when in doubt it is completed with venography.
Educational content. It does not replace supervised hands-on training or your unit's protocols.
References
- Ibeas J, Roca-Tey R, Vallespín J, Moreno T, et al. Spanish Clinical Guidelines on Vascular Access for Haemodialysis (GEMAV). Nefrología. 2017;37(Suppl 1):1-191. doi.org
- Lok CE, Huber TS, Lee T, Shenoy S, et al. KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update. Am J Kidney Dis. 2020;75(4 Suppl 2):S1-S164. doi.org
- Silva MB Jr, Hobson RW 2nd, Pappas PJ, et al. A strategy for increasing use of autogenous hemodialysis access procedures: impact of preoperative noninvasive evaluation. J Vasc Surg. 1998;27(2):302-307. pubmed.ncbi.nlm.nih.gov
- Ferring M, Claridge M, Smith SA, Wilmink T. Routine preoperative vascular ultrasound improves patency and use of arteriovenous fistulas for hemodialysis: a randomized trial. Clin J Am Soc Nephrol. 2010;5(12):2236-2244. doi.org
- Chlorogiannis D, et al. Pre-operative ultrasound mapping before arteriovenous fistula formation: an updated systematic review and meta-analysis. J Nephrol. 2024. doi.org
- Schmidli J, Widmer MK, Basile C, de Donato G, Gallieni M, et al. Vascular Access: 2018 Clinical Practice Guidelines of the European Society for Vascular Surgery (ESVS). Eur J Vasc Endovasc Surg. 2018;55(6):757-818. doi.org
- Sharbidre KG, Alexander LF, Varma RK, et al. Hemodialysis access: US for preprocedural mapping and evaluation of maturity and access dysfunction. RadioGraphics. 2024;44(1):e230053. doi.org