Background: Peripheral nerve blocks effectively alleviate postoperative pain. Animal studies and human research indicate that opioid tolerance results in reduced effectiveness of local analgesics. This applies to both central nerve blockade and infiltration anaesthesia. The impact on peripheral nerve block in humans has not been evaluated. The aim of the study is 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 cause shorter sensory and motor block in opioid-tolerant compared to opioid-naive counterparts.

Methods: Twenty opioid-tolerant individuals will be matched by sex and age with opioid-naïve counterparts. Participants will undergo an ultrasound-guided radial nerve block. The onset time and duration of motor and sensory blockade will be tested and measured. The primary outcome is difference in 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. Perspectives: The data from this study will provide evidence for the duration of peripheral nerve block in opioid tolerant individuals and support if a specific postoperative protocol for opioid tolerant individuals is needed or it should be of special attention.