Mepivacaine local anaesthetic duration in equine palmar digital nerve blocks.
Authors: Bidwell L A, Brown K E, Cordier A, Mullineaux D R, Clayton H M
Journal: Equine veterinary journal
Summary
# Editorial Summary: Mepivacaine Duration in Equine Palmar Digital Nerve Blocks Understanding how long local anaesthetics remain effective is crucial for diagnostic nerve blocking, yet little quantitative data existed on mepivacaine duration in equine palmar digital blocks. Bidwell and colleagues used force plate analysis to measure ground reaction forces in ten horses with unilateral navicular disease, recording peak vertical force before injection and at 15 minutes, 1, 2, and 24 hours post-block. The lame forelimb initially showed significantly reduced loading (4256 ± 204 N versus 5345 ± 188 N in the sound limb), but at 15 minutes post-block this disparity disappeared entirely (5126 ± 129 N versus 5140 ± 184 N), with complete symmetry persisting through the 1-hour mark; by 2 hours loading had begun to redistribute abnormally again (4642 ± 182 N), returning to pre-block patterns by 24 hours. For practitioners relying on diagnostic blocks to localise lameness, these findings indicate a narrow diagnostic window: peak reliability exists between 15 minutes and 1 hour post-injection, after which declining efficacy may compromise clinical interpretation, though residual analgesia extends beyond 2 hours. This timeframe should inform your block scheduling and assessment protocols, particularly when sequential blocks are needed or when distinguishing between different pain sources.
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Practical Takeaways
- •Perform lameness evaluations 15 minutes to 1 hour after palmar digital nerve block to ensure complete analgesic effect before diagnostic interpretation
- •Be aware that some analgesia persists beyond 2 hours, which may influence gait assessment timing in subsequent diagnostic blocks or procedures
- •Plan re-blocking or follow-up procedures accordingly, as mepivacaine effect is substantially diminished by 2 hours but not completely absent
Key Findings
- •Palmar digital nerve block with mepivacaine was fully effective between 15 minutes and 1 hour post-injection, with no significant difference in peak vertical force between lame and contralateral limbs during this period
- •Analgesic effect began to subside between 1 and 2 hours, with mean peak vertical force in the lame limb decreasing from 5126 N at 1h to 4642 N at 2h
- •Sufficient analgesia persisted beyond 2 hours to affect gait characteristics, but by 24 hours vertical forces had returned to pre-block baseline values
- •Pre-block peak vertical force was significantly higher in the non-lame contralateral forelimb (5345 N) compared to the lame forelimb (4256 N)