DOI: 10.1097/aln.0000000000006082 ISSN: 0003-3022

Evaluation of Post-block Hypersensitivity Using Quantitative Sensory Testing Before, During, and After Axillary Brachial Plexus Block Resolution in Healthy Volunteers

Yun-Yun K. Chen, Jenna M. Wilson, Patrick W. Collins, Sheila R. Gokul, Philipp Lirk, Kristin L. Schreiber
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Background:

The problem of a sharp increase in pain after resolution of a nerve block, known as rebound pain, has been increasingly recognized. It is currently unknown whether rebound pain simply reflects the unmasking of untreated, residual surgical pain, or if it represents a de novo hyperalgesic state driven by a mechanistic resetting of pain thresholds in response to regional anesthesia. In this study, we assessed nociceptive processing after a single-injection axillary brachial plexus block in healthy volunteers, to detect whether a previously blocked arm displayed objective hypersensitivity, in the absence of surgical pain.

Methods:

Healthy volunteers received a single-injection axillary brachial plexus block using 15cc of mepivacaine 1.5%, with their contralateral unblocked arm serving as a control. Pain sensitivity between arms was compared using a range of Quantitative sensory testing (QST), comparing punctate, pressure and heat pain using paired t-tests or Wilcoxon sign-rank-tests. The primary outcome was heat pain threshold to 1/10 pain, compared between previously blocked and control arms at 60-minutes post-motor-resolution (MR), with secondary outcomes being other modalities compared at this timepoint. Additionally, we explored differences in maximally sensitized values during the entire post-block period.

Result:

All 40 participants (age:19-64 years, 60% female) completed the study. At 60-minutes post-MR, heat pain threshold to 1/10 pain was not significantly different between arms (block:42.8±2.6°C, control:41.1±0.4°C; p=0.157), nor were other sensory modalities, except for heat pain threshold to 5/10 pain, where control arm was more sensitive than block arm. When examining the maximally sensitized values including 3-hours after MR, the control arm showed greater sensitivity in some tested modalities (punctate pain threshold and painful after sensations), but not others (heat and pressure pain thresholds and tolerances, temporal summation of pain).

Conclusions:

Multimodal pain testing revealed no evidence of post-block hypersensitivity during resolution of a single-injection axillary brachial plexus block.

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