Emergency department (ED) patients commonly present with painful hand injuries requiring anesthesia for exploration, manipulation, drainage, and/or repair. Forearm ultrasound-guided nerve (FUN) blocks by emergency physicians have been described, yet no study has directly compared this technique to anatomic wrist (AW) blocks. This study aims to compare the degree of anesthesia produced by FUN blocks versus AW blocks. Secondary outcomes include subjective perception of anesthesia, and the pain associated with each procedure. This is a prospective randomized double-blinded placebo-controlled study of healthy volunteers. Subjects chose between 1 and 3 nerves (median, ulnar or radial) for nerve block. When a nerve was selected, subjects underwent injections targeting this nerve at bilateral wrists (AW blocks) and bilateral forearms (FUN blocks). One arm was randomly assigned to receive an anesthetic block at the forearm and a placebo block at the wrist, while the other arm received a placebo block at the forearm and an anesthetic block at the wrist. All anesthetic blocks were performed with 3ml of 1% lidocaine buffered (1:10) with sodium bicarbonate. All placebo injections consisted of 3ml of normal saline. A single operator trained in both AW and FUN blocks performed all injections. The operator and subjects were blinded to the contents of the syringes. Objective evaluation of blocks was performed by a blinded observer, performing pinprick tests at pre-selected standard locations on the hand corresponding to the appropriate sensory nerve distribution. Evaluation began 15 minutes after injections, and was repeated at 15-minute intervals for a total of 60 minutes. A block was considered successful if complete anesthesia was obtained at 15 minutes after the injection was finished. Sample size was estimated at 18 pairs of nerves to detect a difference of 45% in block success. 12 subjects underwent blocks of 18 pairs of nerves (3 median, 7 ulnar, 8 radial). Mean time for AW block injection was 35 seconds, and for FUN block injection was 67 seconds. At 15 minutes post injection, 14/18 (78%; 95% confidence interval (CI) 59% to 97%) of nerves blocked using the FUN block were successfully blocked, as opposed to 10/18 (56%; 95% CI 33% to 79%) of nerves blocked using the AW block. Subjects felt that the pain of the procedure was greater in 5/18 (28%; 95% CI 7% to 48%) FUN blocks, and 10/18 (56%; 95% CI 33% to 79%) AW blocks. Subjectively, subjects felt that more complete anesthesia was achieved in 12/18 (67%; 95% CI 45% to 89%) FUN blocks, as opposed to 1/18 (6%; 95% CI -5% to 16%) AW blocks. This preliminary study did not detect a statistically significant difference in hand anesthesia at 15 minutes when comparing forearm ultrasound-guided (FUN) blocks to traditional anatomic wrist (AW) blocks. While there was a trend toward higher block success with FUN blocks, this study was underpowered to detect a difference less than 45% between the 2 techniques. Of note, FUN blocks did result in statistically higher overall subjective anesthesia, and this may be of significant value when applied to patients who require painful procedures to address their injuries. A randomized trial comparing FUN blocks to AW blocks for ED patients with hand injuries is warranted.
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