Stimulation of the posterior cord predicts successful infraclavicular block

Infraclavicular (IC) block is often performed by localizing one cord within the brachial plexus sheath and placing all the local anesthetic solution at that location. We hypothesized that posterior cord stimulation would be associated with a greater likelihood of IC block success. We enrolled 369 patients scheduled for surgery to the lower arm or hand in a prospective, nonrandomized observational trial. All underwent IC blocks using a standard technique, and the cord stimulated immediately before drug injection was recorded. Motor and sensory functioning were evaluated 15 min after injection. Compared with stimulation of either the lateral or medial cord, stimulation of the posterior cord was associated with rapid onset of motor block in significantly more nerves, as well as a decreased likelihood of block failure (motor and sensory block inadequate to perform surgery). Failure rates were 5.8% for posterior cord, 28.3% for lateral (P < 0.05), and 15.4% for medial (P < 0.05). The differences were highly significant when adjusted for multiple possible confounders, such as gender, body mass index, location of the incision, and level of training of the individual performing the block (P < 0.001, lateral versus posterior; P = 0.003, medial versus posterior). A low failure rate was also predicted by stimulation of more than one cord simultaneously (P < 0.05). We conclude that injection after locating the posterior cord or multiple cords predicts successful IC block.