Clinical Articles

Ultrasound in Anaesthesia: System and Probe Setup

2026-10-18 By SonoStarReads 4

Buying ultrasound for an anaesthesia department is not the same as buying it for a radiology department. Radiology wants one system that covers the whole body; anaesthesia wants a guidance tool that can be wheeled into the theatre and be ready within minutes of a puncture. Most of the time it is looking at vessels and nerves a few centimetres deep; occasionally at pleura and heart. That pattern of use puts the emphasis of the configuration somewhere quite different.

1. The four guidance tasks anaesthesia deals with

Task	What is being looked at	Depth range	What imaging has to do well
Peripheral nerve block	The shape and position of the nerve, and the structures around it	Superficial: 2-5 cm is common	Superficial resolution and dynamic observation
Central venous catheterisation (internal jugular, subclavian)	Course of the vein, adjacent artery and pleura	Internal jugular 2-4 cm; subclavian deeper	Superficial resolution plus adjustable depth
Arterial puncture (radial and others)	Vessel cross-section, calibre and course	1-2 cm	Resolution at very shallow depths
Truncal blocks and paravertebral regions	Muscle layers, fascial planes, the target space	3-6 cm is common	Clear layers and good contrast

What these four have in common is that the target structures are all shallow. That is why anaesthesia depends far more on a high-frequency linear probe than on large depth.

2. How to configure the probe

Among the handheld models on this site that can be used for guided puncture, the high-frequency linear and the three-in-one are the two common choices. The difference is whether the work is superficial only, or superficial plus abdomen plus cardiac:

Configuration	Typical model	Frequency and depth (as published)	Suits
High-frequency linear (single head)	5P	10.0-14.0 MHz; scanning depth 20 / 30 / 40 / 55 mm	Radial artery, peripheral veins, superficial nerves, thyroid and other very shallow targets
Dual-head (convex + linear)	5LP / 5CL and similar	Linear 7.5-10.0 MHz (depth 20 / 40 / 60 / 80 mm); convex covers the abdomen	Mainly superficial guidance, with abdominal work and consultations as well
Three-in-one (convex + linear + cardiac)	5CPL	Convex 3.2-5.0 MHz (90 / 160 / 220 / 305 mm), linear 7.5-10.0 MHz (20 / 40 / 60 / 80 mm), cardiac 3.2-5.0 MHz (90 / 120 / 140 / 160 mm)	One device covering nerve blocks, vascular puncture, pre-operative cardiac assessment and pleural examination

If the department only does nerve blocks and vascular puncture, the depth steps of a single high-frequency linear probe (20 / 30 / 40 / 55 mm) already cover the great majority of targets. If pre-operative assessment, pleural examination and abdominal consultations are also needed, the switching capability of the three-in-one is more practical.

3. Sterility and protection

Guided puncture is the step before an invasive procedure, and the sterility requirement cannot be relaxed because it is "only looking":

Probe cover. A sterile cover must be used during puncture; ultrasound gel goes inside the cover and sterile gel outside. The two must not be mixed up.
Cables. The cable has to be brought within the sterile field as well, so that it does not contaminate anything when it crosses the sterile area.
Cleaning the probe. Clean between patients as the instructions require, and avoid disinfection methods that may damage the acoustic lens.
An extra point for handheld systems. The link between probe and phone or tablet is wireless, so the operator holds the probe while the display can stay outside the sterile field - in a cramped theatre this is an advantage rather than a limitation.

4. Where the screen goes decides how smoothly the procedure runs

This is often overlooked but makes a large difference in practice. Most puncture in anaesthesia is one hand on the probe and one on the needle, with the eyes moving between screen and puncture site. There are three options for the screen:

Placement	Suits	Note
Fixed opposite the operator, level with the line of sight	Routine nerve blocks, central venous catheterisation	The screen has to be at eye level; looking down at it breaks the stability of the hand
Slightly in front, on the operator's own side	Where position is restricted, such as lateral or prone	Avoids the operator twisting round, which affects needle control
Shown on the handheld device (phone or tablet)	Very small theatres, bedside	Needs a mount or an assistant holding the screen, so that it does not move

5. Runtime and continuous use

The pattern in anaesthesia is "intermittent but frequent": perhaps a dozen uses in a day, but each one has to work immediately. On the published data, a 5 series handheld probe runs for about 3 hours of uninterrupted scanning, with individual models differing (about 1 hour for 5PA, about 2.5 hours for 5T), and takes about 2-3 hours to charge; intermittent use in practice lasts considerably longer than that figure. The practical approach is to keep one fully charged probe in each theatre, rather than relying on one probe to last the whole day.

6. Three boundaries

Seeing it is not the same as getting there. Ultrasound shows the target and the needle tip, but whether the puncture succeeds depends on anatomy, position, patient cooperation and operator experience. The equipment does not carry the outcome.
Leave room for anatomical variation. The course of vessels and the position of nerves vary between individuals. When the image departs from what was expected, change to another approach or to a landmark technique rather than forcing the original plan.
Guided procedures still need qualifications and protocol. Ultrasound guidance is an aid; the procedure should be carried out by a physician with the relevant qualifications, following the institution's protocol. Indications and contraindications follow the instructions for use and clinical standards.

7. Common questions

Q: Does an anaesthesia department need a three-in-one probe?

A: It depends on the department's tasks. For nerve blocks and peripheral vascular puncture only, a single high-frequency linear probe is enough. Where pre-operative cardiac assessment, pleural examination or part of the abdominal consultation work is involved, the software switching of a three-in-one saves both the probe changes and the cost of carrying several.

Q: Is the signal affected inside a theatre?

A: A handheld probe sends images to the display over Wi-Fi generated by the probe itself, so it does not depend on the theatre having a usable network. Where a theatre is dense with wireless equipment, it is still worth checking connection stability on site the first time it is used.

Q: Can one probe be used for both central venous and radial access?

A: Yes, provided the depth steps can be switched. The radial artery is at 1-2 cm and the internal jugular vein at 2-4 cm, so with the same high-frequency linear probe the 20 / 30 / 40 / 55 mm steps are adjusted between them - the shallow step for the radial, the deeper step for the jugular.

Q: Is a needle guide essential?

A: It is not essential, but it reduces the number of attempts at alignment. Models with a needle guide can display a reference line for the intended insertion angle on screen. The choice between in-plane and out-of-plane approaches is covered in a separate article on this site.