Background: In vertical infraclavicular brachial plexus block, success depends on distal flexion or extension response. Initially, elbow flexion (lateral cord) is generally observed. However, specific knowledge about how to reach the medial or posterior cord is lacking. We investigated the mid-infraclavicular area in undisturbed anatomy and tested the findings in a clinical setting.

Methods: Along a length of 35 mm around the mid-infraclavicular point, cryomicrotomy sections of 5 shoulders from cadavers were used todetermine the topography of the cords in relation to one another and the axillary artery. Based on the findings, the anesthesiologists were instructed on how to elicit a distal motor response after an initial elbow flexion response in single-shot, Doppler-aided, vertical infraclavicular block in a series of 50 consecutive patients.

Results: In the mid-infraclavicular area, the lateral cord always lies anterior to either the posterior or the medial cord and cranial to the axillary artery; the posterior cord was always cranial to the medial cord; and both cords were always located dorsal to the artery. In the clinical study, in 98% of the included patients, finger flexion or finger and/or wrist extension was elicited as predicted. The overall success rate was 92%. No vascular or lung puncture occurred.

Conclusions: In the clinical study, in 98% of cases, the final stimulation response of posterior or medial cord was found as predicted by the findings of the anatomic study. Once elbow flexion is elicited, a further (ie, deeper) advancement of the needle will result in the proper distal motor response.