How Much Volume of Local Anesthesia and How Long Should You Wait After Injection for an Effective Wrist Median Nerve Block?

Abstract

Background: Many surgeons and emergentologists use non-ultrasound-guided wrist nerve blocks. There is little evidence to guide the ideal volume of local anesthesia or how long we should wait after injection before performing pain-free procedures. This pilot study examined time to maximal anesthesia to painful needle stick in 14 volunteer participants receiving bilateral wrist blocks of 6 versus 11 mL of local.

Methods: One surgeon performed all 14 bilateral wrist median nerve blocks in participants who remained blinded until after bandages were applied to their wrist. No one could see which wrist received the larger 11-mL volume injection versus the 6-mL block. Blinded sensory assessors then measured perceived maximal numbness time and numbness to needle stick pain in the fingertips of the median nerve distribution.

Results: Failure to get a complete median nerve block occurred in seven of fourteen 6-mL wrist blocks versus failure in only one of fourteen 11-mL blocks. Perceived maximal numbness occurred at roughly 40 minutes after injection, but actual numbness to painful needle stick took around 100 minutes.

Conclusions: Incomplete median nerve numbness occurred with both 6- and 11-mL non-ultrasound-guided blocks at the wrist. In those with complete blocks, it took a surprisingly long time of 100 minutes for maximal anesthesia to occur to painful needle stick stimuli to the fingertips of the median nerve distribution. Non-ultrasound-guided median nerve blocks at the wrist as described in this article lack reliability and take too long to work.

Keywords: lidocaine; local anesthetic; median nerve block; numbness to pain; time to anesthesia; volume of local anesthetic; wide awake surgery.

Conflict of interest statement

Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.

Each of 14 blinded volunteer participants received bilateral median nerve blocks. Note. One hand received 6 mL, and the other hand was injected with 11 mL in each participant. The red dot indicates the point of injection. Blue indicates the area of visible or palpable local anesthesia. Green indicates the areas of local anesthesia obtained by complete median (and ulnar) nerve blocks.