Perineural Dexmedetomidine Added to Ropivacaine Causes a Dose-dependent Increase in the Duration of Thermal Antinociception in Sciatic Nerve Block in Rat

Abstract

Background The present study was designed to test the hypothesis that dexmedetomidine added to ropivacaine would increase the duration of antinociception to a thermal stimulus in a dose-dependent fashion in a rat model of sciatic nerve blockade. Methods Fifty adult Sprague Dawley rats (10 rats/group) received unilateral sciatic nerve blocks with 0.2 ml of 0.5% ropivacaine or 0.2 ml of 0.5% ropivacaine plus dexmedetomidine (2.7 μM [0.5 μg/kg], 11.7 μM [2 μg/kg], 34.1 μM [6 μg/kg], or 120.6 μM [20 μg/kg]) in a randomized, blinded fashion. Time to paw withdrawal latency to a thermal stimulus for both paws and an assessment of motor function were measured every 30 min after the nerve block until a return to baseline. Results Dexmedetomidine added to ropivacaine increased the duration of dense sensory blockade and time for return to normal sensory function in a dose-dependent fashion (p < 0.005). There was a significant time (p < 0.005), dose (p < 0.005), and time by dose effect (p < 0.005) on paw withdrawal latencies of the operative paws. There were no significant differences in paw withdrawal latencies of the control paws, indicating little systemic effect of the dexmedetomidine. The duration of motor blockade was also increased with dexmedetomidine. High-dose dexmedetomidine (120.6 μM) was not neurotoxic. Conclusion This is the first study showing that dexmedetomidine added to ropivacaine increases the duration of sensory blockade in a dose-dependent fashion in rat. The findings are an essential first step encouraging future efficacy studies in humans.

The effects of bupivacaine combined with different adjuvants on block onset and duration and on ion channel expressions (SCN9A, TRPM) in sciatic nerve block in rats

“…Brummett et al (21) have reported that 0.005% dexmedetomidine with the addition of 0.5% bupivacaine increases sensory and motor block times. Another study reported that ropivacaine added to dexmedetomidine is more likely to cause a sensory block than a motor block (22). Dexmedetomidine increased both the sensory and the motor block in our study, but the increase in the sensory block was greater.…”

“…Dexmedetomidine can be a useful adjuvant to add to local anesthetics during the postoperative period to provide analgesia without affecting mobilization. The perineural administration of dexmedetomidine in humans has not been approved by the Food and Drug Administration (22). On the other hand, there have been no reports of neurotoxicity.…”

Efeitos antinociceptivos, analgésicos e histopatológicos de dexmedetomidina e bupivacaína intratecal em rato

“…These results suggest that dexmedetomidine exerts its effects through α 2 -adrenoceptor agonism. Brummett and colleagues' study investigating addition of dexmedetomidine to ropivacaine induced peripheral nerve block 19 . They administered dexmedetomidine in doses up to 20 μg.kg -1 , and the pH value of mixture of ropivacaine and dexmedetomidine was reported to be 5.69 ± 0.05, which is far more acidic than the pH values of drug mixtures measured in our study.…”

Effect of Multiple Doses of Dexmedetomidine for Moderate Sedation Facilitating Intubation during Nasotracheal Fiberoptic Laryngoscope in Awake Patients-A Randomized Prospective Study

“…It's α 2 -agonists reducing the release of norepinephine. It stimulates central presynaptic α2 receptor resulting in decreased noradrenaline release which in turn causes hypotension and bradycardia [11][12][13][14].…”