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

Abstract

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. 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. 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. 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.