The influence of arm abduction on the anatomic relations of infraclavicular brachial plexus: an ultrasound study.

BACKGROUND: Distances from brachial plexus to the coracoid process and the pleura are critical for performing infraclavicular block. We evaluated the influence of arm abduction on the position of the neurovascular bundle relative to the skin, to the coracoid process and to the pleura using ultrasonography. METHODS: An ultrasound examination of the brachial plexus at the infraclavicular level was performed on 26 patients. Distances from the axillary artery to the skin, to the coracoid process and to the pleura were measured and noted with different degrees of arm abduction (0, 45, and 90). Vertical infraclavicular brachial plexus block was then performed by means of nerve stimulation in 14 additional patients undergoing hand surgery. RESULTS: Under ultrasound examination, the distance from the axillary artery to the skin was found to be significantly less with arm abduction (0 degrees : 32 +/- 7 mm, 45 degrees : 29 +/- 7 mm, 90 degrees : 25 +/- 5 mm, P < 0.05). The distance from the skin to the pleura was 47 +/- 5 mm with a medial deviation of 18 +/- 3 degrees and was not influenced by arm position. Brachial plexus was identified by nerve stimulation at a vertical depth of 41 +/- 7 mm from the skin. CONCLUSION: Abduction of the arm reduces the depth of the brachial plexus but does not change the position of the axillary artery relative to the coracoid process or the pleura. Ultrasonography may under-estimate the actual depth of the plexus.