Indirect versus direct measurement of brachial plexus depth

Supraclavicular nerve blocks are effective but may be complicated by pneumothorax. We hypothesized that, to avoid this complication, the depths of the brachial plexus and the lung could be estimated to guide needle placement. In 17 patients undergoing surgical relief of thoracic outlet syndrome, we designated a point on the skin midway between the clavicle and the trapezius muscle, in line with the most lateral point of the arterial pulsation in the supraclavicular fossa, to make preoperative height measurements relative to the clavicle and then intraoperative depth measurements of the plexus, artery, and pleura. The height of the reference point above the top of clavicle did not differ significantly from the depth of the plexus. The height of the reference point above the top, middle, and bottom of the clavicle differed significantly from the pleural depth (P = 0.0001, P = 0.0001, P = 0.0005, respectively). Patient weight correlated significantly with the depth of the plexus (P = 0.004, r(2) = 0.45), artery (P = 0.0003, r(2) = 0.42), and pleura (P = 0.0003, r(2) = 0.58). We conclude that it is possible to accurately estimate the depth of the brachial plexus in the supraclavicular fossa. Implications: In this study, we sought to minimize the risk of pneumothorax when approaching the brachial plexus through the supraclavicular fossa by developing a technique that could accurately estimate the depth of the nerves, within a range that is well clear of the lung.