Key messages

• Compared to anatomical landmarks, using ultrasound guidance for neuraxial anaesthesia in adults reduces the number of attempts until success, and the procedure (needling) time. Success is defined as either the number of times the needle is advanced following a backward movement, or the number of times it punctures the skin.

• Ultrasound guidance likely increases the rate of success on the first try.

• Ultrasound guidance may make little to no difference to participant satisfaction or technical failure. Technical failure might include the need to change to general anaesthesia, or the need to discontinue the procedure for neuraxial anaesthesia, or whether the person experienced the intended anaesthetic effect.

• We do not know whether ultrasound guidance affects pain during the procedures and adverse events.

• Ultrasound guidance in neuraxial anaesthesia probably has some benefits, but uncertainties remain.

What is neuraxial anaesthesia?
Neuraxial anaesthesia is performed by injecting a local anaesthetic into the spaces surrounding the spinal cord, usually the spinal or epidural space, or a combination. It is a common technique for numbing a specific area of the body, used mainly for surgery or during labour. In neuraxial anaesthesia, the doctor places a needle between the vertebrae (backbones). Once the doctor finds the right spot, he or she will either inject the anaesthetic directly, or place a thin tube, called a catheter, into the space, through which they can inject the anaesthetic. Successful neuraxial anaesthesia, with as few attempts as possible, is important to reduce complications.

What is ultrasound and how it might work?

Ultrasound uses high-frequency sound waves to create images of the inside of the body. The doctor uses a handheld device, called a probe, to send ultrasound waves into the body and create pictures. Conventional neuraxial anaesthesia is performed by using specific anatomical points on the body as a guide. Sometimes the needle does not reach the targeted space, because the anatomical position the doctor thought he or she found by touching the area can be off a bit from the actual position. Ultrasound allows the doctor to see the local anatomy of interest and the size of important structures, and helps to figure out how deep and in what direction to insert the needle.

Two ultrasound-guided methods are commonly used. In the first one, ultrasound is used before the needle is inserted, or pre-procedural. The second one is referred to as real-time, which means the needle is inserted first, then moved to the correct spot while watching the ultrasound images.

What did we want to find out?

We wanted to find out whether it was better to use ultrasound or anatomical landmarks to guide the needle for neuraxial anaesthesia in adults. We also wanted to find out whether ultrasound guidance led to similar unwanted effects as anatomical landmarks.

What did we do?

We searched for studies that investigated ultrasound guidance compared with anatomical landmarks for neuraxial anaesthesia in adults. We compared and summarised the results of the studies, and rated our confidence in the evidence, based on factors, such as study methods and sizes.

What did we find?
We found 65 studies with 6823 people. Studies were conducted in Africa, Asia, Europe, the Middle East, North America, and Oceania. Four studies evaluated real-time ultrasound as an intervention.

• Compared to anatomical landmarks, ultrasound guidance reduces the number of attempts required for successful placement of the needle by an average of 0.41 attempts per person, and reduces the procedure (needling) time by an average of 34 seconds.

• Ultrasound guidance likely increases the success rate for first attempts: 778 people out of 1000 experienced successful first attempts with ultrasound guidance, compared to 556 people out of 1000 with anatomical landmarks.

• Ultrasound guidance may result in little to no difference in participant satisfaction or technical failure.

• Ultrasound guidance may have little to no effect on pain during procedures or unwanted effects, but we are very uncertain about the results.

What are the limitations of the evidence?
We are moderately to highly confident in our findings regarding the number of attempts, the length of time for the procedure, and the rate of first-attempt success.

We have little confidence in the evidence for:

• Participant satisfaction, because it was difficult to hide who received ultrasound guidance. The results were very inconsistent across the different studies.

• Technical failure, because there were not enough studies to be certain about the results of this outcome.

• Pain during the procedure, because it was difficult to hide who received ultrasound guidance. The results were very inconsistent across the different studies, and the results included both those who experienced pain and those who did not.

• Unwanted effects, because it was difficult to hide who received ultrasound guidance, and there were not enough studies to be certain about the results. This outcome should also be interpreted with caution, because there were a variety of definitions in each study, such as back pain or headache.

How up to date is this evidence?
The evidence is up-to-date to November 2023.