Effects of Intraneural Injection of Dexmedetomidine in Combination With Ropivacaine in Rat Sciatic Nerve Block

Background and Objectives Dexmedetomidine is known to have neural protection effect via attenuation of inflammatory responses induced by local anesthetics. We investigated whether intraneural dexmedetomidine is effective for attenuating or preventing neural injury resulting from inadvertent intraneural injection of local anesthetic. Methods Rats were randomly divided, and left sciatic nerve was surgically exposed. The rats received no injection (control group) or intraneural injections of 0.2 mL of normal saline (saline group), 0.2 mL of 0.5% ropivacaine (ropivacaine group), or 0.2 mL of 0.5% ropivacaine and 0.5 g/kg of dexmedetomidine (ropivacaine plus dexmedetomidine group). Interleukin (IL)-6 and IL-1 messenger RNA (mRNA) levels were detected at 60 minutes after intraneural injection in experiment 1 (5 per group). Sensory and motor functions were assessed until the return of normal sensory and motor functions, and histopathological and ultrastructure analysis were performed at 4 weeks after intraneural injection in experiment 2 (8 per group). Results Dexmedetomidine with ropivacaine better enhanced sensory and motor blockade than ropivacaine alone. IL-6 (3.2 1.0 vs 5.9 +/- 2.1), IL-1 (1.1 +/- 0.1 vs 2.2 +/- 0.7) levels, scores of axon and myelinated fiber degeneration (1 [0-2] vs 2 [1-3]), and demyelinated fiber percentages (20.1 +/- 10.4 vs 48.3 +/- 12.7) were lower in the ropivacaine plus dexmedetomidine group than in the ropivacaine group. No animals showed any signs of permanent neurological deficit. Conclusions Intraneural dexmedetomidine has sensory and motor blockade-enhancing effects, anti-inflammatory properties, and protective effects against neural injury. These findings suggest that dexmedetomidine as an adjuvant has beneficial effects in rat when intraneural injection of local anesthetic occurs.