An evaluation of the brachial plexus block at the humeral canal using a neurostimulator (1417 patients): The efficacy, safety, and predictive criteria of failure

To evaluate the efficacy and safety of the multiple peripheral nerve block technique at the humeral canal (humeral block) with the use of a neurostimu lator, we prospectively studied 1417 patients undergoing upper limb surgery with a brachial plexus block at the humeral canal (1468 blocks). The succe ss rate (defined as sensory block [in all nerve distributions] and/or the a bsence of another anesthetic technique required to allow surgery) was 95%. The threshold of minimal stimulation used to locate each nerve before injec ting the anesthetic solution was the unique predictive factor for identifie d failure. For the median nerve, the threshold was 0.8 mA with a relative r isk of failure (RRf: relative risk evaluated by series of Taylor with a 95% confidence interval) = 1.49 (P = 0.04), for the radial nerve the threshold was 0.6 mA (RRF 1.3, P = 0.02), and 0.7 mA for the ulnar nerve (RRF 1.36, P = 0.04). For any equal or higher stimulation level, the risk of failure o f the humeral block increased. For the musculocutaneous nerve, we did not o bserve a significant stimulation threshold for the risk of failure; althoug h beyond 0.7 mA, the RRF was always more than 1.3. Adverse events occurred in 7% of all cases and were usually minor (nausea/vomiting, anxiety, local pain). Our study provides supplementary information on the efficacy and saf ety of this technique. Stimulation thresholds are clinically identified for the first time as the main factor linked to the failure of a technique usi ng a neurostimulator. We conclude that the humeral block is a reliable peri pheral block allowing good success rates results with minor complications, which can be used as an alternative to the axillary block.