Single-stimulation, low-volume infraclavicular plexus block: Influence of the evoked distal motor response on success rate

Background and Objectives: We compared the success rate of single-injection infraclavicular plexus block by using electrically evoked radial, ulnar, or median nerve-type distal motor response to guide the injection of local anesthetic. Methods: Consecutive patients requiring surgery distal to the upper arm were prospectively included in this study over a 6-month period. No search for predetermined distal motor responses was performed. The first qualifying distal motor response evoked for a stimulating current intensity of < 0.5 mA distributed patients into 3 groups of patients. The study was continued until 3 groups of 60 patients were fulfilled. Twenty to 25 minutes after the injection of 30 mL of 1.5% mepivacaine, blinded evaluation of block quality was performed. A successful block was defined by the presence of a complete sensory block of the 5 major nerve distal distributions of the arm. Results: Five hundred patients were included. The first evoked distal motor response was of radial, median, and ulnar nerve type in 46% (n = 230), 42% (n = 210), and 12% (n = 60) cases, respectively. The success rate of the infraclavicular plexus block was significantly higher when the injection was performed on a radial nerve-type response (90%) as compared with the median (74%) or ulnar (68%) nerve distal motor response. Intraoperative sedation and general anesthesia were not needed. None of the patients experienced specific complications. Conclusion: We showed that evoked distal motor response influenced the success rate of single-injection infraclavicular plexus block. The highest success rate was obtained when injection was performed after radial nerve-type motor response.