title: Transient heat hyperalgesia during resolution of ropivacaine sciatic nerve block in the rat.
abstract: BACKGROUND
  Preliminary studies using perineural sciatic ropivacaine in rat demonstrated unexpected heat hyperalgesia after block resolution. To better characterize the time course relative to mechanical anesthesia-analgesia, we tested the hypothesis that ropivacaine 0.5% leads to transient heat hyperalgesia in rats independent of mechanical nociception. We also evaluated functional toxicity (eg, long-term hyperalgesia and/or tactile allodynia 2 weeks after injection).
  
  
  METHODS
  Under surgical exposure, left sciatic nerve block was performed in 2 groups of adult male rats-ropivacaine (200 μL, 5 mg/mL; n = 14) versus vehicle (n = 11). The efficacy and duration of block were assessed with serial heat, mechanical (Randall-Selitto testing), and tactile (von Frey-like monofilaments) tests; motor-proprioceptive (rotating rod) and sedation tests were used at 1 and 7 hrs after injection. The presence of nerve injury was assessed by repeating the heat, tactile, and motor tests 12 to 14 days after injection.
  
  
  RESULTS
  Ropivacaine-induced anesthesia was fully manifest at 1 hr after injection. At 3 hrs after injection, heat hypersensitivity was present in the setting of resolved mechanical analgesia. All behavioral measures returned to baseline by 2 weeks after injection. There was no evidence of (i) behavioral sedation, (ii) persistent changes in heat or mechanical sensitivity, or (iii) persistent changes in proprioceptive-motor function at 12 to 14 days after injection.
  
  
  CONCLUSIONS
  Ropivacaine 0.5% induces transient heat hyperalgesia in the setting of resolved mechanical analgesia, further suggestive of modality and/or nociceptive fiber specificity. Whether this finding partially translates to "rebound pain" after patients' nerve blocks wear off requires further study.
authors: Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA. kolarczyklm@upmc.edu
authors: Lavinia M
authors: LM
authors: Kolarczyk
authors: Brian A
authors: BA
authors: Williams
mesh_terms: D000577:Amides / Q000008:administration & dosage / Q000633:toxicity*; D000818:Animals; D001340:Autonomic Nerve Block / Q000009:adverse effects*; D006358:Hot Temperature / Q000009:adverse effects*; D006930:Hyperalgesia / Q000139:chemically induced* / Q000503:physiopathology; D008297:Male; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077212:Ropivacaine; D012584:Sciatic Nerve / Q000502:physiology; D013997:Time Factors; D014110:Touch / Q000502:physiology
chemical_list: D000577:Amides; D000077212:Ropivacaine