Author(s): ,
Western University, Anesthesia & Perioperative Medicine, London, Canada
Western University, Anesthesia & Perioperative Medicine, London, Canada
Western University, Anatomy & Cell Biology, London, Canada
ESRA Academy. Sehmbi H. Sep 13, 2017; 190901; 240
Herman Sehmbi
Herman Sehmbi

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Background and Aims:

The interscalene brachial plexus block, used to manage shoulder pain, is associated with a high incidence of phrenic nerve blockade.1 The posterior approach to the suprascapular nerve (SSN) has inferior analgesic efficacy and a higher technical failure rate.2 The sub-omohyoid suprascapular (SOS) nerve block has been found to be a technically easy and reliable technique3, besides providing comparable efficacy. However, its proximity to the brachial plexus may result in extension of injectate to the phrenic (or accessory phrenic) nerve. We hypothesized that the use of limited volumes (5 ml) of injectate will limit this spread.


We identified the suprascapular nerve (SSN) in the supraclavicular fossa under the inferior belly of omohyoid muscle, using the method described by Siegenthaler et al.3 Using a linear transducer (13-6 MHz, SonoSite X-porte) and an in-plane approach (50 mm, 22G insulated needle, PajunkÒ), we deposited 5 ml injectate (15 ml methyl cellulose: 10 ml NaCl: 5 ml methylene blue dye) bilaterally in four fresh cadavers. We dissected the supraclavicular region of the neck exposing the brachial plexus, its branches, and the phrenic nerve. We evaluated the extent of dye spread in immediate proximity to the brachial plexus, phrenic nerve and SSN. We graded the intensity of dye staining (1+ to 3+) and measured the length of nerve stained (phrenic and SSN, figure 1).


These are summarised in table 1.


A 5 ml injection for SOS block appears to provide an optimal volume, without spread to the phrenic nerve. Further clinical studies are required for confirmation. 

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