Ultrasound Technique for Vascular Access: Short-Axis, Long-Axis, and Dynamic Guidance

Comprehensive guide to ultrasound technique for vascular access: probe selection, short-axis vs long-axis approach, in-plane vs out-of-plane needle guidance, dynamic vs static technique, and practical tips for needle visualization.

guide•Feb 2026•Ultrasound-Guided Access

Ultrasound Technique for Vascular Access: Short-Axis, Long-Axis, and Dynamic Guidance

Ultrasound guidance for vascular access is not a single technique — it includes multiple probe orientations, needle-to-probe relationships, and guidance strategies. Each approach has distinct advantages and learning considerations. Selecting the appropriate technique for the clinical scenario and achieving real-time needle visualization are the keys to safe, efficient US-guided access.

Parent guide: Ultrasound-Guided Vascular Access: Complete Reference

Probe Selection

Frequency

High-frequency linear probe (7.5–15 MHz): Preferred for all vascular access procedures. High frequency produces high-resolution images at shallow depths (0.5–5 cm). Superior for visualizing vessel walls, needle tips, and surrounding structures in the arm and neck.

Lower-frequency curvilinear probe (2–5 MHz): Used for deeper structures; not appropriate for peripheral vascular access. Rarely needed for standard vascular access procedures.

Selection: For PIV, midline, and PICC: use the highest-frequency linear probe available (10–15 MHz preferred). For IJ CVC: 7.5–10 MHz. For femoral CVC: 7.5–10 MHz (deeper vessel).

Probe Orientation Marker

The probe has an orientation marker (groove, bump, or lit indicator) on one side. On the US screen, the corresponding indicator dot (typically top-left corner of image) marks which side of the image corresponds to the indicator side of the probe.

Standardize orientation before every procedure: With the indicator to the patient’s right side (or cephalad for IJ), the indicator dot on screen corresponds to the patient’s right (or head). Disorientation about which side of the screen is which is a common cause of needle misidentification.

Probe Views: Transverse vs. Longitudinal

Short-Axis (Transverse) View

What you see: Cross-section of the vessel — a round or oval dark circle. Adjacent structures (artery, nerve, fascia layers) are visible in the same frame.

Probe orientation: Perpendicular to the vessel long axis.

Advantages:

  • Vessel diameter can be measured (important for catheter-to-vein ratio)
  • Adjacent structures (artery, nerve) are clearly visualized simultaneously
  • Easier for beginners to identify and confirm target vessel
  • Can identify multiple vessels in one view

Disadvantages:

  • Needle appears as a bright dot only when the US beam bisects it — the image shows a cross-section of the needle at one point along its length. If the needle tip is not where the bright dot appears, you may not be tracking the actual tip.
  • The “bright dot” may be the needle shaft, not the tip — a common source of inadvertent vessel wall puncture

Needle-to-probe relationship in short-axis: The needle enters from one side of the probe (out-of-plane technique) and is visible only when the US beam passes through it.

Long-Axis (Longitudinal) View

What you see: The vessel in long cross-section — an elongated channel running across the screen. The vessel appears as two parallel echogenic lines with a dark lumen between them.

Probe orientation: Parallel to the vessel long axis.

Advantages:

  • Needle can be seen along its entire length (in-plane technique)
  • Tip identification is more reliable — you can see the needle advance through the tissue and enter the vessel lumen
  • Better visualization of the needle-vessel relationship during advancement

Disadvantages:

  • Requires precise alignment of the probe with the vessel long axis; slight rotation takes the vessel out of view
  • Cannot simultaneously visualize adjacent structures (artery, nerve) in the same view
  • Requires more practice to maintain vessel in view while advancing needle

In-Plane vs. Out-of-Plane Needle Guidance

These refer to the relationship between the needle and the ultrasound beam plane:

Out-of-Plane (Short-Axis, Static)

The needle enters perpendicular to the ultrasound beam. The probe is in short-axis (transverse) view. The needle appears as a bright dot on screen.

Tracking the tip: Move the probe toward the needle tip as you advance — maintain the needle dot in the center of the screen by “chasing” it with the probe. When you see the dot suddenly disappear below the vessel wall, the tip has entered the vessel lumen.

Pitfall: “Walking” the probe ahead of the actual needle tip. If you move the probe without advancing the needle, the bright dot disappears — but the needle hasn’t moved. Inexperienced operators often mistake the shaft for the tip.

Technique to identify true tip: Jiggle the needle (small back-and-forth motion) — the true tip location jiggle will appear on the US image. If no movement is seen, the probe is no longer over the needle.

In-Plane (Long-Axis, Dynamic)

The needle enters parallel to the ultrasound beam. The probe is in long-axis (longitudinal) view. The needle is visible as a hyperechoic line along its entire length.

Advantages: The entire needle shaft and tip are simultaneously visible; unambiguous needle tip identification.

Challenges: Requires precise probe alignment with both the vessel long axis AND the needle axis. The needle must enter from the end of the probe — the access “footprint” is longer.

Technique: Approach the probe from the short-side (not the long end). The needle enters from one end of the rectangular probe footprint, at an angle that brings it along the imaging plane.

Practical Recommendation

Most vascular access clinicians use short-axis/out-of-plane for initial vessel identification and single-lumen PIV (faster setup, easier vein identification) and long-axis/in-plane for PICC and CVC (better needle tip visualization for more complex procedures).

Dynamic vs. Static Technique

Dynamic (real-time) guidance: Ultrasound is used continuously throughout the entire needle advancement — the probe is on the patient while the needle is being advanced.

Static technique: Ultrasound is used before needle insertion to mark the vessel location on the skin, then the probe is removed and the needle is advanced to the marked location without real-time guidance.

Evidence: Dynamic (real-time) guidance is superior to static technique for first-attempt success and complication reduction. All current guidelines (NICE TA49, INS 2021) recommend dynamic real-time ultrasound guidance for CVC insertion and challenging peripheral access.

When static technique is used: Occasionally used when a second operator is unavailable and the clinician cannot hold the probe and advance the needle simultaneously. A sterile probe cover and additional operator are standard for PICC insertion.

Practical Procedure Tips

Setting Up

  1. Open machine, select linear probe, set depth to 2–4 cm for upper arm veins
  2. Apply sterile probe cover (for sterile procedures) and sterile gel on insertion field, or non-sterile gel for site assessment
  3. Identify target vessel before prepping patient skin

Needle Visualization Optimization

Use a high-angle approach: Steep needle angle (45°+) makes the needle more perpendicular to the US beam — creating a brighter reflection. However, steep angle also means less control for small peripheral veins. Find the angle that provides good visualization while allowing controlled advancement.

Avoid very shallow angles for initial venous entry: Shallow angles reduce needle visualization; compensate by using long-axis technique for shallow angle approaches.

Jiggle for confirmation: If uncertain whether the bright structure is the needle or another structure, jiggle the needle 1–2 mm — the needle-specific movement will distinguish it from static tissue.

Hydrolocation: Inject 0.5–1 mL of saline through the needle while watching the US image — saline injection into tissue creates a visible “water balloon” expansion; injection into the vessel creates visible turbulence in the lumen. Useful for confirming intraluminal position.

After Vessel Cannulation

Confirm intraluminal position before advancing guidewire or catheter:

  • Blood return in flashback chamber
  • Long-axis view confirming guidewire in vessel lumen (guidewire is highly echogenic)
  • Compression test: with guidewire in place, apply probe pressure — guidewire should remain in position even as the vein compresses around it (vein is not completely collapsible once guidewire is present)

Related guides:

Related policies:

References

  1. Troianos CA, et al. (2011). Guidelines for performing ultrasound guided vascular cannulation. Anesth Analg, 114(1):46–72.
  2. Brass P, et al. (2015). Ultrasound guidance for CVC insertion. Cochrane Database Syst Rev, (1):CD011447.
  3. NICE Technology Appraisal No. 49. (2002). Guidance on the use of ultrasound locating devices for placing CVC catheters. London: National Institute for Clinical Excellence.
  4. Lamperti M, et al. (2012). International evidence-based recommendations on US-guided vascular access. Intensive Care Med, 38(7):1105–1117.