Effects of dexmedetomidine combined with ropivacaine on sciatic and femoral nerve blockade in dogs

Objective To evaluate motor and sensory blockade of combining dexmedetomidine with ropivacaine, administered perineurally or systemically, for femoral and sciatic nerve blocks in conscious dogs. Study design Randomized, controlled, experimental study. Animals Seven healthy Beagle dogs, aged 3.3 +/- 0.1 years and weighing 11.0 +/- 2.4 kg. Methods Dogs were anesthetized with isoflurane on three separate occasions for unilateral femoral and sciatic nerve blocks and were administered the following treatments in random order: perineural ropivacaine 0.75% (0.1 mL kg(-1)) on each nerve and intramuscular (IM) saline (0.2 mL kg(-1)) (GCON); perineural dexmedetomidine (1 mu g mL(-1)) and ropivacaine 0.75% (0.1 mL kg(-1)) on each nerve and IM saline (0.2 mL kg(-1)) (GDPN); and perineural ropivacaine 0.75% (0.1 mL kg(-1)) on each nerve and IM dexmedetomidine (1 mu g mL(-1), 0.2 mL kg(-1)) (GDIM). Nerve blocks were guided by ultrasound and electrical stimulation and dogs were allowed to recover from general anesthesia. Sensory blockade was evaluated by response to clamp pressure on the skin innervated by the saphenous/femoral, common fibular and tibial nerves. Motor blockade was evaluated by observing the ability to walk and proprioception. Sensory and motor blockade were evaluated until their full recovery. Results No significant differences in onset time to motor and sensory blockade were observed among treatments. Duration of motor blockade was not significantly different among treatments; however, duration of tibial sensory blockade was longer in the GDPN than in the GDIM treatment. Conclusions and clinical relevance Although a longer duration of sensory blockade was observed with perineural dexmedetomidine, a significant increase compared with the control group was not established. Other concentrations should be investigated to verify if dexmedetomidine is a useful adjuvant to local anesthetics in peripheral nerve blocks in dogs.