Electric Nerve Stimulation Does Not Correctly Predict Needle-Nerve Distance and Potential Local Anesthetic Spread for Interscalene Brachial Plexus Blockade.

This study evaluated electric nerve stimulation as a nerve location tool. After eliciting motor response in 43 patients undergoing shoulder surgery, the needle tip's position, distance from the closest nerve, and spread of saline were evaluated using ultrasound imaging. The needle's tip resided 1 to 4 mm from the closest nerve in 21, in direct contact with it in 7, and 6 to 18 mm away in 15 patients. In 21 patients, subsequent saline dissection did not reach the brachial plexus. Thus, the success rate of electric nerve stimulation for correct needle-nerve distance identification was 48.8%, with correct fluid spread reached in only 51.2% of patients.