Ultrasound guidance has become the standard of care for central venous access, and for good reason — it measurably reduces failed attempts, mechanical complications, and the number of needle passes compared with a landmark-based approach. The sonographer's role spans three distinct moments: assessing and selecting the vessel beforehand, guiding the needle in real time, and confirming the result afterward.

Before the Needle: Vessel Assessment

For Central Lines (Internal Jugular, Subclavian, Femoral)

Internal jugular vein is the most common target and the one ultrasound guidance benefits most clearly.

Position: head turned slightly away from the side of insertion, slight Trendelenburg to distend the vein
Confirm it's the vein, not the artery: thin-walled, easily compressible, dilates with Valsalva or gentle abdominal pressure, no pulsatile flow on spectral Doppler. The carotid artery lies deep and medial to the IJ in the standard approach — know the relationship before anyone reaches for a needle
Assess patency along the length you'll be scanning — a partially thrombosed or unusually small vein changes the plan before the first pass, not after

Subclavian vein is harder to image directly due to the clavicle, and lines here are still frequently placed with a landmark technique, though a supraclavicular ultrasound-guided approach to the subclavian/innominate junction is increasingly used and worth knowing.

Femoral vein: straightforward to visualize, medial to the femoral artery. Higher infection and thrombosis risk than IJ or subclavian makes this more of a short-term or emergency access choice.

For PICCs

Target veins: basilic vein (preferred — larger caliber, more superficial, more comfortable long-term), cephalic vein, or brachial vein.

Vein mapping before insertion:

Measure diameter at the planned insertion site — most protocols want at least 3–4 mm for a PICC, more if a multi-lumen catheter is planned, since the catheter should occupy no more than about 45% of the vessel diameter to reduce clot risk
Confirm patency along the intended path proximally, since a downstream stenosis or old thrombus changes catheter tip trajectory
Check for duplicated veins, which are common in the basilic system and matter for planning
Note depth from skin — very deep or very superficial veins both bring specific technical challenges the inserter needs to know about in advance

During Placement: Needle Guidance

In-Plane vs Out-of-Plane

Out-of-plane (short-axis): The vessel appears as a circle in cross-section; the needle appears as a bright dot as it crosses the beam. This is the more commonly used approach for central lines — it gives a clear view of the vessel's relationship to adjacent structures, though the needle tip position within the image can be less certain moment to moment.

In-plane (long-axis): The vessel and the full length of the needle are visualized together in the same plane. This gives continuous visualization of the needle tip, which many operators prefer for smaller or more superficial vessels like those used for PICCs, though it demands more precise probe-needle alignment to keep both in the same plane throughout the advance.

Many experienced operators use a hybrid approach — starting out-of-plane to confirm vessel position and relationship to the artery, then transitioning to in-plane as the needle approaches the vessel wall for the final advance.

The Sonographer's Role During Insertion

Keep the vessel centered in the image throughout
Watch for tenting of the vessel wall as the needle approaches — the wall depressing without puncturing means more pressure or a steeper angle is needed
Confirm needle tip position within the vessel lumen, not just proximity to it, before the operator advances the wire
Watch for the wire advancing smoothly within the vessel on ultrasound where feasible — resistance or an unexpected path can indicate the wire has entered a side branch or exited the vessel

After Placement: Confirming Position

Rapid Bedside Confirmation

Ultrasound can quickly confirm several things immediately after the procedure:

No new pneumothorax — for IJ or subclavian approaches, assess for lung sliding bilaterally, comparing pre- and post-procedure if a baseline was obtained
No hematoma at the insertion site or along the vessel
The catheter within the vessel, where directly visualizable, rather than in an unintended location

The "Bubble Test" for Tip Position

For central lines and PICCs, confirming catheter tip position at the cavoatrial junction is typically done by chest X-ray or intraprocedural ECG-based tip confirmation — but a rapid ultrasound-based method exists:

With a subxiphoid or apical cardiac view established, inject agitated saline rapidly through the catheter
Watch for microbubbles appearing in the right atrium, and note the timing of their arrival — a very rapid, turbulent appearance suggests the tip is well-positioned near the cavoatrial junction, while a delayed or absent bubble signal after a properly timed injection raises concern about tip position or line patency

This technique is a useful adjunct in real time, particularly in settings without immediate chest X-ray access, but does not universally replace formal tip-position confirmation per your institution's protocol — know which is required and when ultrasound serves as the primary versus supplementary check.

Vascular Complications to Recognize

Arterial puncture: Pulsatile bright red return, or ultrasound showing needle/wire tract entering the artery instead of the vein — stop immediately, hold pressure, and reassess vessel anatomy before another attempt.

Vessel thrombosis, new or pre-existing: Non-compressible vein with intraluminal echogenic material — relevant both as a reason to select a different site and as a post-procedure complication to screen for.

Hematoma: A developing anechoic-to-complex collection adjacent to the vessel, sometimes with a visible bleeding source on color Doppler if the puncture is recent.

Catheter malposition — for PICCs, the tip advancing into the internal jugular vein instead of continuing centrally is a recognized and identifiable complication, sometimes visible on ultrasound of the neck immediately after insertion if suspected.

Key Images to Capture

Pre-procedure vessel assessment — diameter, patency, and depth at the planned site
Vessel-to-artery relationship, with color Doppler distinguishing the two
Needle-in-vessel confirmation during the procedure
Post-procedure — lung sliding bilaterally (for IJ/subclavian approaches)
Post-procedure — insertion site assessed for hematoma
Bubble study images if performed for tip confirmation

Reporting Language

Pre-procedure vein mapping: "Right basilic vein assessed for PICC placement. Diameter at the planned insertion site 4.2 mm, patent and compressible throughout the visualized course, without duplication. Depth from skin surface 8 mm. No pre-existing thrombus identified."

Post-procedure confirmation: "Following right internal jugular central line placement, bilateral lung sliding is present with no evidence of pneumothorax. No hematoma at the insertion site. Agitated saline injected through the catheter produces prompt right atrial opacification on subxiphoid view, consistent with an appropriately positioned catheter tip; formal tip confirmation per institutional protocol is recommended."

SonoBuddy is a reference tool for sonographers. Vascular access technique and tip-position confirmation requirements are set by institutional protocol and the proceduralist.

Ultrasound-Guided Vascular Access: Central Lines and PICCs