In experienced hands, ultrasound provides at least as good success rates as other methods of peripheral nerve location. Individual studies have demonstrated that ultrasound may reduce complication rates and improve quality, performance time, and time to onset of blocks. Due to wide variations in study outcomes we chose not to combine the studies in our analysis.
Ultrasound- or nerve stimulation-guided wrist blocks for carpal tunnel release: a randomized prospective comparative study.
We hypothesized that ultrasound-guided wrist blocks may be faster to perform, and may increase success rate, compared with nerve stimulation-guided wrist blocks.
                Sixty patients undergoing ambulatory endoscopic carpal tunnel release were randomly allocated to receive median and ulnar nerve blocks using either sensory-motor nerve stimulation (n = 30) or ultrasound guidance (n = 30). Four mL of mepivacaine 1.5% was injected around each nerve. Performance time and onset time of complete sensory block were assessed.
                Median time to perform both median (ultrasound, 55 [48-60] vs. nerve stimulation, 100 [65-150] seconds, P = .002) and ulnar (ultrasound, 57 [50-70] vs. nerve stimulation, 80 [60-105] seconds, P = .02) nerve blocks were significantly shorter in the ultrasound group. Onset time of complete sensory block in the median (ultrasound, 370 [278-459] vs. nerve stimulation, 254 [230-300] seconds, P = .02) and ulnar (ultrasound, 367 [296-420] vs. nerve stimulation, 241 [210-300] seconds, P = .01) nerve areas were shorter in the nerve stimulation group. The success rate was 93% in both groups.
                This randomized prospective study demonstrates that ultrasound-guided wrist nerve blocks are as efficient as those performed with nerve stimulation.