A Single Needle Tip Position Approach 'The Middle Trunk' Block-for Supraclavicular Block: An Anatomic Cadaveric Study

Using conventional anatomical landmark or nerve stimulator guidance, injection of local anesthetic following paresthesia of the middle two fingers resulted in >97% block efficacy. "Corner pocket" and "intracluster" injections during ultrasound-guided supraclavicular brachial plexus have been suggested for better dermatomal coverage but have limitations. We hypothesized that a single injection of dye at the level of the middle trunk (MT) would result in diffusion in the superior and inferior trunks.

After ethics approval, ultrasound-guided injections were performed with a needle tip positioned within fatty connective tissue at the level of the MT bilaterally in 6 soft-embalmed cadavers. We injected 3.5, 7.5, and 15 ml diluted methylene blue dye in 2 cadavers each. Bilateral neck dissections were performed in the posterior triangle of the neck 30 min after injection in all cadavers to visualize the dye spread.

Injection of the lower volume of dye (3.5 ml) spared the superior trunk, suprascapular and phrenic nerve (except 1 specimen), while an injection of the higher volume of dye (15 ml) consistently stained all trunks after a single injection at MT level. Similarly, the suprascapular and phrenic nerves were congruously stained with 15 ml injections, while with 7.5 ml 50% times, the PN was soaked. Dye dispersion in cadaveric brachial plexuses was deep with 15 ml and mild-to-moderate stain pattern with others.

We postulate that the use of a single injection MT block technique with an injectate volume of 7.5 ml or more can be an effective technique for a supraclavicular brachial plexus block. However, the findings of this cadaveric study need substantiation from clinical studies.