Ultrasound-guided fistula cannulation: in-plane vs out-of-plane

Ultrasound-guided cannulation lets you see the vein, the needle and its tip while you cannulate an AV fistula. Here you will learn when to use it, how to handle the probe and how to choose between the in-plane and out-of-plane approaches. Written for hemodialysis nurses and physicians who are new to ultrasound.

Updated October 10, 2026 · 11-minute read

When is ultrasound-guided cannulation indicated?

You don't need it for every cannulation. Nefrología al día considers it especially useful for first cannulations and indicates it for patients with obesity, very deep vessels or fistulas that are difficult to cannulate blind [1]: because of poor maturation, juxta-anastomotic stenosis, accessory veins or collaterals, or hematomas from previous cannulations [1]. A tortuous vein also makes blind cannulation harder.

KDOQI 2019 considers it reasonable to use ultrasound to determine the direction of flow and proper needle placement in select patients, performed by trained operators: for example, at the first cannulation of a new AVF or after an infiltration [2]. It does not recommend ultrasound for every patient because the evidence is limited, results depend on the operator and it takes resources [2]. The Spanish GEMAV guideline describes it as a highly valuable aid for difficult native fistulas [3]. And first cannulations matter: a single infiltration before the first successful two-needle cannulation is associated with 56% lower odds of the fistula maturing [2].

What the evidence shows in AV fistulas

• Eves 2021 (randomized trial; 32 patients with difficult fistulas, 346 cannulations): fewer additional needle passes (72 vs 99) and fewer additional skin punctures (10 vs 25), with no more pain or complications, but slower cannulation [4].
• Chen 2023 (randomized trial; 50 patients with complex fistulas and a handheld scanner): first-attempt success of 96% vs 72% and less pain, with similar time [5].

These are small trials in difficult accesses: they don't prove that ultrasound improves every cannulation.

Equipment and setup

• High-frequency linear probe (7.5–12.5 MHz): high resolution and shallow penetration, exactly what a superficial vessel needs [1].
• Scanner: a portable or handheld device is enough; spectral Doppler is only essential for measuring flow [1].
• Asepsis: strict aseptic technique [3]; some centers use a sterile probe cover and sterile gel [1].
• Arm: relaxed and supported on a firm surface.
• Image: vein in the upper half of the screen, focus at the back wall and gain set so the lumen looks black.

Probe handling: orientation and PART maneuvers

Hold the probe in one hand and the needle in the other, with your eyes on the screen [1], and rest the edge of your probe hand on the patient's arm. Before you cannulate, slide the probe toward the marker side and watch which way the image moves: failing to match the patient's side with the side of the screen is a typical beginner error [9]. To fine-tune the image, use the PART mnemonic from regional anesthesia:

• Pressure: on a fistula, as little as possible. Pressing the AVF with the probe can even cause thrombosis [1]. Use plenty of gel and let the probe almost "float".
• Alignment: slide the probe to center the vessel or follow the needle.
• Rotation: turn it to go from short axis to long axis.
• Tilt: rock it so the beam hits the wall and the needle perpendicularly.

Move one thing at a time. In a study of 520 ultrasound-guided blocks, residents' two most common errors were advancing the needle without seeing it and unintentional probe movement [9].

Finding the vein and telling it from the artery

Start in short axis (transverse). Follow the arterialized vein from the anastomosis, measure its diameter and depth, look for stenosis, aneurysms, thrombus or collaterals, and choose a straight, healthy segment. Distances from the anastomosis and between needles follow your protocol (see the needle angle, gauge and spacing guide).

• Compressibility: veins flatten with light pressure; the artery stays round and pulsatile.
• Continuity: the fistula vein arises from the anastomosis and runs superficially.
• Doppler: shows the direction of flow before you place the needles [2] (see the AV fistula Doppler guide).
• Neighbors: identify the artery and nearby nerves so you don't puncture them [1].

Long-axis (in-plane) approach

The probe lies along the vein and the needle enters at one end of the probe, on its midline, within the beam. On the screen you see the whole needle as a bright line, from the skin to the tip, including when it crosses the wall and advances along the lumen. That is why Nefrología al día calls it the recommended approach for fistula cannulation [1].

How to do it

1. Center the vein in short axis and rotate the probe 90° without losing it, until it appears as a horizontal tube.
2. Insert the needle right at the end of the probe, on its midline, at your protocol's angle (for an AVF, about 25°, depending on depth) [3].
3. Advance only when you can see the tip. If the needle disappears, it has left the plane: bring it back with tiny rotations or slides of the probe, not by moving the needle.
4. You'll see the anterior wall indent and give way, and flashback appears. As in standard cannulation, lower the angle and advance along the center of the lumen, keeping the tip away from the back wall.

Drawbacks: the beam is only a few millimeters thick, so keeping alignment takes a steady hand; you lose sight of lateral structures, and on a tortuous vein only a short straight segment fits in the image. The flatter the needle, the better you see it, because metal reflects sound like a mirror.

Short-axis (out-of-plane) approach and DNTP

The probe sits across the vein, which appears as a circle, and the needle crosses the imaging plane. You see only a bright dot, often with a comet tail: the cross-section of the needle where it passes through the beam, which may be the tip or any point along the shaft. You can easily center the vessel and see what lies on either side, but the needle is visible only when it crosses the field, so you have to sweep the probe to follow it; that is why it is the less used approach for fistulas [1].

The big risk is mistaking the shaft for the tip. In a mannequin study, 64% of residents punctured the back wall of the internal jugular vein in short axis, even though they felt confident about needle position [6].

Dynamic needle tip positioning (DNTP)

1. Insert the needle on the probe's midline, a few millimeters from it [1]. The deeper the vessel, the farther back you need to start.
2. Advance the needle until the bright dot appears.
3. Slide the probe away from the insertion point until the dot disappears, then back just enough to see it again: that last visible dot is the tip.
4. Advance the needle 1–2 mm, slide the probe again and repeat until the tip sits in the center of the circle.
5. Once you get flashback, lower the angle and follow the tip a few more millimeters, step by step.

With DNTP, short axis outperformed long axis among novices on a phantom (success 97% vs 81%) [7] and in radial artery cannulation (first-pass success 97.9% vs 83.3%) [8]. No trial has compared the two approaches in AV fistulas: applying these data is an extrapolation, and practice varies between units.

In-plane vs out-of-plane: comparison

Tenting, the "pop", flashback and the saline flush check

Before it gives way, the anterior wall indents under the tip: this is tenting. When the needle goes through, you feel a "pop" and the tent disappears. Flashback tells you the bevel has reached the lumen, but not whether the tip is centered: check the screen before you lower the angle and advance.

If you flush the needle with saline before connecting, with the probe in place, the image confirms the position:

• Tip in the lumen: saline goes in without resistance and its microbubbles form a plume of bright echoes traveling along the vein from the tip.
• Tip outside the lumen: a black fluid collection appears around the vessel, with pain and swelling. That is an infiltration: stop and reposition the needle (see the infiltration guide).

The same principle, saline microbubbles as a contrast agent, is used to confirm central venous catheter position [11]; there are no specific studies in AV fistulas.

Common mistakes and how to avoid them

• Back-wall puncture (transfixion): the tip exits through the side or back wall and causes infiltration or a hematoma [2]. Lower the angle as soon as you are in and don't advance without seeing the tip [1,6].
• Advancing without seeing the needle, moving the probe by accident or reversed orientation [9]: anchor your hand, check the marker and move one thing at a time.
• Pressing with the probe: the vein flattens, looks shallower and may thrombose [1].
• Partial volume: the beam has thickness, so a needle beside the vein can look as if it were inside. Confirm in both axes and with the saline flush.

Ergonomics: keep the screen in your line of sight

Place the scanner in front of you, on the far side of the arm, with your eyes, the insertion site and the screen in line. In a study of short-axis radial artery cannulation, displaying the image this way raised success from 70% to 100% and cut the time from 68 to 29 seconds [10].

Learning curve, courses and simulation training

Ultrasound-guided cannulation has a learning curve: in the Eves trial, part of the extra time was attributed to staff being new to the technique [4], and in the mannequin study, more training was associated with fewer back-wall punctures [6]. KDOQI considers structured, supervised training before first cannulations reasonable, and notes that simulation may be beneficial and should be studied [2].

Ultrasound-guided cannulation training for nurses usually combines theory, practice on a phantom or simulator, and supervised cannulations. A simulator such as Fistulab lets you rehearse hand-screen coordination, tip tracking and recognizing tenting and infiltration without risk. It does not replace supervised practice with patients.

Educational content. It does not replace supervised hands-on training or your unit's protocols.

References

1. Moyano Franco MJ, Salgueira Lazo M, Roca-Tey R. Punción ecoguiada del acceso vascular para hemodiálisis [Ultrasound-guided cannulation of hemodialysis vascular access]. In: Lorenzo V, López Gómez JM (eds). Nefrología al día. 2023. In Spanish. nefrologiaaldia.org
2. Lok CE, Huber TS, Lee T, et al. KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update. Am J Kidney Dis. 2020;75(4 Suppl 2):S1–S164. doi.org
3. Ibeas J, Roca-Tey R, Vallespín J, et al. Spanish Clinical Guidelines on Vascular Access for Haemodialysis (GEMAV). Nefrologia. 2017;37(Suppl 1):1–191. doi.org
4. Eves J, Cai P, Latham R, et al. A randomised clinical trial of ultrasound guided cannulation of difficult fistulae for dialysis access. J Vasc Access. 2021;22(4):635–641. doi.org
5. Chen S, Liu JS, Chai CC, et al. Handheld ultrasound-guided cannulation of difficult hemodialysis arteriovenous access: a randomized controlled trial. Hemodial Int. 2023;27(1):21–27. doi.org
6. Blaivas M, Adhikari S. An unseen danger: frequency of posterior vessel wall penetration by needles during attempts to place internal jugular vein central catheters using ultrasound guidance. Crit Care Med. 2009;37(8):2345–2349. doi.org
7. Clemmesen L, Knudsen L, Sloth E, Bendtsen T. Dynamic needle tip positioning: ultrasound guidance for peripheral vascular access. A randomized, controlled and blinded study in phantoms performed by ultrasound novices. Ultraschall Med. 2012;33(7):E321–E325. doi.org
8. Mesa BK, Sinha M, Kumar M, et al. Radial arterial cannulation by ultrasound-guided dynamic needle-tip positioning using the short-axis out-of-plane approach versus the long-axis in-plane approach: a randomized controlled study. Cureus. 2024;16(2):e54183. doi.org
9. Sites BD, Spence BC, Gallagher JD, et al. Characterizing novice behavior associated with learning ultrasound-guided peripheral regional anesthesia. Reg Anesth Pain Med. 2007;32(2):107–115. doi.org
10. Tsuchiya M, Mizutani K, Funai Y, Nakamoto T. In-line positioning of ultrasound images using wireless remote display system with tablet computer facilitates ultrasound-guided radial artery catheterization. J Clin Monit Comput. 2016;30(1):101–106. doi.org
11. Vezzani A, Brusasco C, Palermo S, et al. Ultrasound localization of central vein catheter and detection of postprocedural pneumothorax: an alternative to chest radiography. Crit Care Med. 2010;38(2):533–538. doi.org