Patterns of Distribution of the Nerves Around the Axillary Artery Evaluated by Ultrasound and Assessed by Nerve Stimulation During Axillary Block.

Our objective was to define the positions of the nerves around the brachial artery and, secondarily, to assess the risk of intraneural injection during dual guided axillary block. Sixty ultrasound-guided axillary blocks were performed. The locations of the musculocutaneous, median, ulnar, and radial nerves relative to the brachial artery were determined. The position of the ulnar nerve was defined in relation to that of the brachial vein, and the position of the musculocutaneous nerve in relation to the coracobrachialis muscle. The locations were confirmed by neurostimulation and injection of local anesthetic was avoided when the current intensities were below 0.3 mA. The incidences of intraneural injection and postblock neurological injury were recorded. The median nerve was located in the upper external quadrant in 89% of cases and the ulnar nerve in the upper internal quadrant (95%), superficial (19%), or deep (81%) to the brachial vein. The radial nerve was located in the lower internal quadrant in 97% of cases, and the musculocutaneous nerve in the lower external quadrant in 85%. Its disposition differed depending on its proximity to the artery (106 ± 26°) or whether it was inside the coracobrachialis muscle (119 ± 15°; P = 0.023). Three intraneural injections were observed (0.5%, one in the median and two in the radial nerves) and no patient had postblock neuropathy. Our study evidences slight anatomical variability among the neural structures in the axillary region and confirms the safety of the axillary technique with double monitoring, using ultrasound to monitor the approach of the needle to the nerve and nerve stimulation at currents > 0.3 mA to reduce the incidence of intraneural injection. Clin. Anat., 2018. © 2018 Wiley Periodicals, Inc. 2018.