Where should the tip of the needle be located in ultrasound-guided peripheral nerve blocks?

Abstract

The ultrasound appearance of nerves and target injections are better understood. The specific distributions of local anaesthetic spread that predict success are significantly different from one anatomical site to another. It seems advisable to avoid intraneural injection.

High Opening Injection Pressure Is Associated With Needle-Nerve and Needle-Fascia Contact During Femoral Nerve Block

“…19,20 Ultrasonography is highly user-dependent and requires technical skill, adequate sonoanatomy, and high-quality ultrasonographic equipment. 21 Hence, inadvertent placement of the needle tip against the nerve prior to injection and intraneural injection may go undetected by ultrasound. 22 Such risk may be much higher with multiple injection techniques, which are common in clinical practice of ultrasound-guided nerve blocks.…”

Histological confirmation of needle tip position during ultrasound-guided interscalene block: a randomized comparison between the intraplexus and the periplexus approach

“…Nevertheless, avoidance of ''intraneural injection'', which is defined by injection below the epineurium, is standard practice within the regional anesthesia literature. 3,5,13,23 Nerves cannot be dissected and removed in live patients, while comparing block techniques requires thousands of patients due to the low but clinically significant rate of neurological complications. 24 We chose the cadaver model followed by microscopic assessment of tissues in an attempt to clarify exactly which neural layers are penetrated with an intraplexus vs a periplexus approach.…”

“…1,2 This may be due to the limitation of conventional ultrasound to distinguish muscle fascia from epineurium and small fascicles, [3][4][5] such that mechanical nerve injury, barotrauma, or local anesthetic toxicity may result from unintended injection into critical nerve structures. 1,[6][7][8][9][10] This has recently led investigators to focus on how best to avoid nerves while still achieving a reliable block.…”

Injection Through the Paraneural Sheath Rather Than Circumferential Spread Facilitates Safe, Effective Sciatic Nerve Block

“…Circumferential spread around the nerve often involves multiple needle redirections and repeated injection, heightening the risk of neural injury, prolonging block performance time, and intensifying patient discomfort. 5 In contrast, puncture through the paraneural sheath and deposition of local anesthetic beyond this layer not only simplifies the procedure but also avoids potential complications associated with the circumferential spread method. In fact, similar observations have been reported for interscalene blocks, where successful blockade is achieved by less aggressive injection into a fascial sheath distinct from the nerve.…”

“…6 Perhaps the key to a safe, effective block with rapid onset is to inject local anesthetic through the appropriate sheath or layer of connective tissue into the correct fascial plane rather than completely encompassing the nerve and attaining the doughnut sign. 5 Further studies are required to evaluate the effectiveness of this concept for blocks at different sites.…”