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

Background: 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.

Methods: 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.

Results: 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.

Conclusion: 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.