Landmark Versus Ultrasound-Guided Puncture

Puncture has long relied on surface anatomical landmarks and reasoned estimation. Ultrasound guidance adds one more layer of information on top of that: seeing it in real time.

One thing should be said first: the two are not substitutes for each other; each has situations where it fits. This article sets out the differences, to help decide which to use and when.

1. How the two methods differ in principle

The landmark method uses bony landmarks, surface projections of anatomy, surface measurement and the operator's experience to estimate where the target structure lies and how deep it is, then inserts along the estimated path.

Visual guidance uses ultrasound to show the target structure, the surrounding tissue and the needle in real time, with the image updating throughout the insertion.

One caution: how much of the needle you see under visual guidance depends on the scan plane. Out-of-plane shows only a single bright dot - the needle's cross-section - it is not visible along its length. This is covered in more detail in "In-Plane or Out-of-Plane: How to Choose the Needle Approach for Ultrasound-Guided Puncture".

2. Which patients and sites each one suits

The comparison below is not about which is better, but about the conditions under which one is usually reached for first.

One point worth stressing: for superficial punctures, either method can be used. Which one is chosen is the operator's judgement, depending on the patient's condition, the operator's own proficiency and the setting. There is no single answer that applies to everything.

3. What visual guidance changes in the procedure

Adding ultrasound puts three extra steps into the workflow, and these are the substantive changes:

1. Before inserting: an assessment step

Before the needle goes in, look at this patient's particular situation:

• Position and course of the target - which direction it runs on the surface, and whether it is straight
• Relation to adjacent structures - artery and vein, nerve, tendon, bone, pleura
• State of the lumen or structure - whether it is patent, and whether anything is abnormal
• Anatomical variation - individual differences are a fact; the standard position is not enough

Once this step is done, every later step has something to stand on.

2. During insertion: the path can be adjusted as things actually are

• Advance in steps - confirm the tip after each short advance rather than pushing all the way in one movement
• If the needle is poorly seen, find it first - check whether the probe plane is aligned with the needle path; do not keep advancing blindly
• Angle control - too steep an angle makes the tip harder to see; as long as the tip stays visible, a relatively shallow angle is better

3. After insertion: more ways to confirm position

• Aspiration - confirm the tip is not inside a vessel
• Watching spread or course - watch the direction of injectate spread while injecting, or the course of the device when placing a catheter
• Keeping the images - they can be stored and exported, which helps with review and discussion

4. Two common misunderstandings

1. "With ultrasound, technique no longer matters." It does. Probe pressure, insertion angle and hand-eye coordination are still basic skills. The commonest example: too much probe pressure collapses the vein, and the vessel then seems to have disappeared from the screen. That is a technique problem, not an equipment problem.

2. "If the dot is on screen, the needle is where it should be." It is not. In out-of-plane view the dot may be the tip, or it may be some part of the shaft further back. The tip has to be tracked point by point by advancing and withdrawing the probe; otherwise it is easy to believe the needle is still shallow when it has already gone too deep.

5. Common questions

6. Choosing the probe

For guided puncture at superficial sites, a high-frequency linear probe is the usual choice: the higher frequency gives better resolution of superficial structures.

Selection reference:

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

Not sure which one to specify? Our Probe Configuration Guide for Vascular Access covers probe and parameter comparisons for different puncture scenarios; ask our product team for a copy.

Summary

1. The landmark method works by estimation, visual guidance by real-time image; each has its own situations - they do not replace one another
2. Where the relation between target and surrounding structures has to be seen, visual guidance helps more
3. What visual guidance really changes is three steps: assessment before, an adjustable path during, confirmation after
4. How much of the needle you see depends on the scan plane - out-of-plane gives only one dot
5. Probe technique is still a basic skill; too much pressure collapses the vein
6. For superficial puncture choose a high-frequency linear probe, and pick the model by depth