Duration of peripheral nerve blocks in opioid-tolerant individuals: A study protocol.

Background: Peripheral nerve blocks effectively alleviate postoperative pain. Animal studies and human research suggest that opioid tolerance may reduce the effectiveness of local analgesics. The reduced effectiveness has been observed in opioid-tolerant humans and animals undergoing spinal and infiltration anaesthesia with both lidocaine and bupivacaine. However, the impact on peripheral nerve blocks in humans has not been evaluated. This study aims to assess the onset time and duration of a radial nerve block in opioid-tolerant individuals compared to opioid-naive individuals. We hypothesise that peripheral nerve blocks may be less effective in producing sensory and motor blockades in opioid-tolerant individuals compared to their opioid-naive counterparts.

Methods: Twenty opioid-tolerant individuals will be matched by sex and age with opioid-naïve counterparts. Participants will receive an ultrasound-guided radial nerve block. The primary outcome is the difference in the duration of sensory nerve blockade between the two groups. The secondary outcomes include the onset time of sensory blockade, onset time of motor blockade, and difference in duration of motor nerve blockade.

Conclusion: This study will compare the effectiveness of a peripheral nerve block between opioid-tolerant and opioid-naïve individuals. Any found differences could support a specific postoperative protocol for opioid-tolerant individuals regarding the use of peripheral nerve blocks.