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Abstract
Background and Aims Injection of local anesthetic with anatomical landmark following paraesthesia of the middle two fingers results in >97% block efficacy. Injections in ‘Corner pocket’ and ‘Intra-cluster’ in the supraclavicular brachial plexus under ultrasound-guidance have been suggested for better coverage. 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, 12 ultrasound guided injection was performed with needle tip positioned within fatty connective tissue at the level of the MT bilaterally in 6 soft embalmed cadavers. We injected 3.5ml, 7.5ml and 15ml diluted methylene blue dye in 2 cadavers (4 specimens) each. Bilateral neck dissections was performed in the posterior triangle of the neck 30 minutes after injection in all cadavers and dye spread was visualized beneath investing layer of deep cervical fascia. (figure 1)
Results Injection of the lower volume of dye (3.5ml) consistently spared the superior trunk while an injection of the higher volume of dye (15ml) consistently stained all trunks when a single injection was performed at the MT level. Suprascapular nerve and phrenic nerves were consistently stained with 15 ml injections while they were spared with low and intermediate-volume injections. The dissections revealed dye dispersion with a dense (15ml) to differential stain pattern (3.5ml and 7.5ml resulted in a mild to moderate) of the cadaveric brachial plexuses. (figure 2)
USG and dissection images for MTB
Distribution of MBD in cadavers: numerical representation
Conclusions We propose the use of a single injection MT block technique using an injectate volume more than 7.5ml for an effective supraclavicular brachial plexus block.