Central Venous Access: Internal Jugular & Subclavian

Central venous puncture is routine work in anaesthesia, critical care and the emergency department. Where to enter and at what angle used to be judged from surface landmarks; with ultrasound, those judgements can be made while looking at the vessel.

This article looks at the two most common routes - the internal jugular vein and the subclavian vein - and works through the ultrasound assessment before puncture, the choice of scan plane, control of needle angle and depth, and several details that are easy to overlook.

1. Before the needle goes in: what ultrasound should show you

The point of the pre-puncture scan is to understand this particular patient before the needle is inserted:

1. Position and course of the target vein - which direction it runs on the surface, and whether the course is straight
2. Its relation to the adjacent artery - the relative position of artery and vein varies between patients; look before you act
3. State of the lumen - whether it is patent, and how the calibre responds to breathing and to posture
4. Anatomical variation - individual differences are a fact; do not work from the textbook position alone
5. Surrounding structures - nerves, the dome of the pleura (particularly on the subclavian route), the thyroid and other neighbouring tissue

The assessment is not a formality. Once these steps are done, every later step has something to stand on.

2. The internal jugular vein: recognising it on ultrasound

Position. The internal jugular vein runs alongside the carotid artery in the neck, in most cases anterolateral to it, but individual variation is marked - what ultrasound shows is what counts.

What to look for:

Compressibility is the most practical way to tell vein from artery: press lightly with the probe and the vein collapses while the artery does not. But note - too much pressure will collapse the vein as well, and it then reads as a small vessel or as no vessel at all. This is the most common problem for beginners.

How to scan. Place the probe on the neck, find the vessel bundle in transverse (short-axis) view first, identify how artery and vein relate, then decide whether to turn to a longitudinal view depending on how you intend to advance the needle.

3. The subclavian vein: watch the adjacent structures

Position. The subclavian vein lies next to the subclavian artery, anteromedial to it, with the dome of the pleura immediately below. The anatomy here is complex, and individual variation has to be judged from what ultrasound shows.

What to look for:

• The same two signs - compressibility and pulsation - separate vein from artery
• The clavicle casts an acoustic shadow behind it and limits the view; approach obliquely from the lower edge of the clavicle, or adjust probe position and angle to find an acoustic window
• In some patients the view stays limited by the clavicle. Take the time to adjust, and do not force the needle in

A particular caution: the subclavian route runs close to the dome of the pleura, so its position belongs in the assessment of the needle path.

4. Short axis (out-of-plane) or long axis (in-plane)

This is the central choice in ultrasound-guided puncture, and each method suits different situations.

Short axis / out-of-plane

• Probe orientation: long axis of the probe perpendicular to the vessel
• On screen: the vessel appears in cross-section, as a circle
• Needle direction: perpendicular to the long axis of the probe
• What you see of the needle: its cross-section, as a single bright dot
• Advantage: the relation of the vessel to surrounding structures (artery, nerve) is easy to see, and it is quicker to learn
• Watch out: only one point of the needle is visible, so the tip has to be tracked by advancing in small steps

Long axis / in-plane

• Probe orientation: long axis of the probe parallel to the vessel
• On screen: the vessel appears along its length
• Needle direction: aligned with the long axis of the probe
• What you see of the needle: the whole shaft and the tip
• Advantage: tip and shaft can be watched continuously in real time
• Watch out: the probe plane has to stay strictly aligned with the needle path; a small deviation takes the needle off the image

How to choose

If the system offers both in-plane and out-of-plane needle guides, they can be used alongside each other when switching between the two scan planes.

5. Controlling needle angle and depth

1. Angle. The shallower the angle, the longer the segment of needle visible in the ultrasound plane - but the longer the subcutaneous path. Too steep an angle and the tip becomes harder to see. As a rule, choose a relatively shallow angle as long as the tip stays visible.

2. Depth. Aim to pass just through the anterior wall of the vein; avoid going deeper than needed. Watch where the tip is as it advances and insert in steps.

3. Advance in steps. Do not push all the way in one movement. Advance a little, check the tip position, then advance again.

4. Blood return is not the end of the procedure. After flashback, the guidewire and catheter position still have to be confirmed according to your institution's protocol.

6. Six details that are easy to miss

1. Too much probe pressure - the vein wall is thin and collapses under light pressure. Too much pressure makes the vessel look smaller than it is, or makes it seem to disappear. Keep the hand light.
2. Looking only at the vessel - especially on the subclavian route, keep the position of the pleura and other adjacent structures in mind throughout.
3. Gain and depth not set - an image that is too bright or too dark directly affects how well the tip can be judged. Set the image so that wall and tip are both clearly distinguishable before inserting.
4. Ignoring individual variation - anatomical variation exists; the textbook position is only a reference, and what ultrasound shows is what counts.
5. Coupling and sterile technique - puncture is an invasive procedure, so the probe has to be protected to sterile requirements.
6. Watching the dot but not the tip - in out-of-plane view there is only one bright dot on screen. Without stepping the needle and tracking the tip, it is easy to believe the needle is still shallow when it has already gone too deep.

7. Choosing the probe

Central venous access is a superficial procedure, so a high-frequency linear probe is the usual choice: the higher frequency gives better resolution of superficial structures, so the vessel wall, the needle tip and the surrounding tissue can be seen clearly.

Selection reference:

The model is chosen together with the patient's build, the depth of the puncture site and the operator's own technique.

The above is the general version. The Probe Configuration Guide for Vascular Access and the full Ultrasound Probe Selection Table set out probe and parameter comparisons for different puncture scenarios; ask our product team for a copy.

Summary

1. Before inserting, look at position and course, relation to the artery, state of the lumen, variation, and adjacent structures
2. Compressibility is the most practical way to tell vein from artery - but keep the probe hand light
3. On the subclavian route, pay particular attention to the dome of the pleura
4. Out-of-plane shows structural relations, in-plane shows the whole needle; the two can be combined
5. Keep the angle shallow and advance in steps; after flashback, still complete the standard confirmation
6. For superficial access choose a high-frequency linear probe, and pick the model by build and depth