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 rat independent of mechanical nociception. We also evaluated functional toxicity (e.g., long-term hyperalgesia and/or tactile allodynia 2 weeks post-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 was assessed with serial heat, mechanical (Randall-Selitto testing), and tactile (von Frey-like monofilaments) tests; motor-proprioceptive (rotarod) and sedation tests were employed 1 hr and 7 hr post-injection. The presence of nerve injury was assessed by repeating the heat, tactile, and motor tests 12–14 days post-injection. Results Ropivacaine-induced anesthesia was fully manifest at 1 hr post-injection. At 3 hr post-injection, heat hypersensitivity was present in the setting of resolved mechanical analgesia. All behavioral measures returned to baseline by 2 wk post-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 12–14 days post-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.

A New Step Toward Evidence of In Vivo Perineural Dexamethasone Safety

“…In this animal model, we also noticed a transient hypersensitivity to heat in the R group as previously described. 23 This hypersensitivity seemed to be corrected with perineural dexamethasone but not with systemic dexamethasone (Fig. 3).…”

Thermal Hyperalgesia After Sciatic Nerve Block in Rat Is Transient and Clinically Insignificant

“…In the comparison study, Kolarczyk and Williams 5 found a statistically significant difference in PWL at 3 hours after the ropivacaine injection from baseline in the treated hind limb (baseline PWL = 9.04 T 2.64 vs 3-hour assessment = 5.5 T 2.34, n = 14 rats), but no evidence of heat hyperalgesia was detected at 5 hours, 7 hours, or at 2 weeks after the block. 5 The present analyses indicate only a short-lived period of hyperalgesia at the 240-minute time point and no other differences or trends to suggest hyperalgesia following the nerve block at any of the other time points assessed ( Table 2), illustrating that this slight degree of hypersensitivity is a transient phenomenon.…”

Obstetric Anesthesiologists as Perioperative Physicians: Improving Peripartum Care and Patient Safety

“…Authors suggest that this may be due to rebound pain [92,93]. Ultimately, TAP blocks may reduce or delay opioid use during the first 2-24 h postoperatively, after which patients may require greater opioid consumption to compensate for the transient hyperalgesia experienced during block regression [91].…”