A low dose of three local anesthetic solutions for interscalene blockade tested by thermal quantitative sensory testing: a randomized controlled trial
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This randomized double-blind controlled trial compared the block characteristics of three low-dose local anesthetics at different roots in an ultrasound-guided interscalene block, using thermal quantitative sensory testing for assessing the functioning of cutaneous small nerve fibres. A total of 37 adults scheduled to undergo shoulder arthroscopy were randomized to receive 5 mL of either 0.5% levobupivacaine with and without epinephrine 1/200,000 or 0.75% ropivacaine in a single-shot interscalene block. Thermal quantitative sensory testing was performed in the C4, C5, C6 and C7 dermatomes. Detection thresholds for cold/warm sensation and cold/heat pain were measured before and at 30 min, 6, 10 and 24 h after infiltration around C5. The need for rescue medication was recorded. No significant differences between groups were found for any sensation (lowest P = 0.28). At 6 h, the largest differences in sensory thresholds were observed for the C5 dermatome. The increase in thresholds were less in C4 and C6 and minimal in C7 for all sensations. The analgesic effect lasted the longest in C5 (time × location mixed model P < 0.001 for all sensory tests). The time to rescue analgesia was significantly shorter with 0.75% ropivacaine (P = 0.02). The quantitative sensory findings showed no difference in intensity between the local anesthetics tested. A decrease in block intensity, with minimal changes in pain detection thresholds, was observed in the roots adjacent to C5, with the lowest block intensity in C7. A clinically relevant shorter duration was found with 0.75% ropivacaine compared to the other groups. Trial registration NCT 02691442.
KeywordsNeurosensory effects Peripheral nerve blocks Thermal quantitative sensory testing
Assistance with the study: Mrs. Annick Leroy for reviewing the statistical analysis. This manuscript has been edited by American Journal Experts.
LS conceived the study, participated in its design and coordination, performed the blocks, analyzed the QST results and wrote the manuscript. GH helped conceive the study design, performed the QST interpretation, helped in the analysis of the data, assisted in manuscript drafting and edited the various versions of the manuscript. TS helped in the analysis of the data, assisted in writing and reviewed the manuscript. SM assisted in writing and reviewing the manuscript. KW performed the statistical analysis. MB helped conceive the study design and performed a critical reading. CS performed QST testing and collected data. MV critically read the various versions of the manuscript.
Financial support and sponsorship: resources were provided from the Department of Anesthesiology only.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Informed consent was obtained from all individual participants included in the study.
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