Perineural dexmedetomidine provides an increased duration of analgesia to a thermal stimulus when compared with a systemic control in a rat sciatic nerve block.
OBJECTIVE
The present study was designed to test the hypothesis that perineural dexmedetomidine provides a longer duration of analgesia than the same dose given subcutaneously in a peripheral nerve block in rats.


METHODS
Fifty-four rats received unilateral sciatic nerve blocks along with a subcutaneous injection at the base of the neck by a blinded investigator assigned at random. Combinations were as follows: perineural ropivacaine alone and subcutaneous (SQ) saline, perineural ropivacaine plus dexmedetomidine and SQ saline, perineural ropivacaine and SQ dexmedetomidine, perineural dexmedetomidine alone and SQ saline, and perineural saline and SQ dexmedetomidine. The ropivacaine concentration was fixed at 0.5%, and the dose of dexmedetomidine was 20.0 microg/kg (119.3 micromol/L). Sensory analgesia was assessed by paw withdrawal latency (PWL) to a thermal stimulus every 30 mins after the block for a minimum of 240 mins or until the return of normal sensory function. The unblocked paw served as the control for assessment of systemic, centrally mediated analgesia. Between-group and within-group comparisons of PWL were obtained for measures from operative and control paws.


RESULTS
The analgesic effect of perineural dexmedetomidine was superior to that of subcutaneous dexmedetomidine in ropivacaine sciatic nerve blocks from time points 120 to 210 mins (P < 0.017). Perineural dexmedetomidine also showed less systemic effect as measured by the unblocked control paw at multiple time points (P < 0.05). Perineural dexmedetomidine alone provided a brief, partial sensory block.


CONCLUSIONS
Sensory analgesia provided by dexmedetomidine added to ropivacaine for peripheral nerve blocks in rat is a peripherally mediated effect.
Brummett
Chad M
CM
Division of Pain Medicine, Department of Anesthesiology, University of Michigan Health System, 1500 E Medical Center Dr, 1H247 UH, Box 0048, Ann Arbor, MI 48109, USA. cbrummet@umich.edu
Amodeo
Francesco S
FS
Janda
Allison M
AM
Padda
Amrita K
AK
Lydic
Ralph
R
D058647:Adrenergic alpha-2 Receptor Agonists / Q000008:administration & dosage*; D000577:Amides / Q000008:administration & dosage; D000698:Analgesia; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage*; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D020927:Dexmedetomidine / Q000008:administration & dosage*; D009407:Nerve Block; D051381:Rats; D017207:Rats, Sprague-Dawley; D057897:Reflex, Righting / Q000187:drug effects; D000077212:Ropivacaine; D012584:Sciatic Nerve
D058647:Adrenergic alpha-2 Receptor Agonists; D000577:Amides; D018712:Analgesics, Non-Narcotic; D020927:Dexmedetomidine; D000077212:Ropivacaine; D003000:Clonidine