Effects of perineural administration of ropivacaine combined with perineural or intravenous administration of dexmedetomidine for sciatic and saphenous nerve blocks in dogs

OBJECTIVE To evaluate the effects of using ropivacaine combined with dexmedetomidine for sciatic and saphenous nerve blocks in dogs. ANIMALS 7 healthy adult Beagles. PROCEDURES In phase 1, dogs received each of the following 3 treatments in random order: perineural sciatic and saphenous nerve injections of 0.5% ropivacaine (0.4 m L/kg) mixed with saline (0.9% NaCl) solution (0.04 mL/kg; DEXOPN), 0.5% ropivacaine mixed with dexmedetomidine (1 mu g/kg; DEXIPN), and 0.5% ropivacaine mixed with dexmedetomidine (2 mu g/kg; DEX2PN). In phase 2, dogs received perineural sciatic and saphenous nerve injections of 0.5% ropivacaine and an IV injection of diluted dexmedetomidine (1 mu g/kg; DEXIIV). For perineural injections, the dose was divided equally between the 2 sites. Duration of sensory blockade was evaluated, and plasma dexmedetomidine concentrations were measured. RESULTS Duration of sensory blockade was significantly longer with DEXIPN and DEX2PN, compared with DEXOPN; DEXIIV did not prolong duration of sensory blockade, compared with DEXOPN. Peak plasma dexmedetomidine concentrations were reached after 15 minutes with DEXIPN (mean +/- SD, 348 +/- 200 pg/mL) and after 30 minutes DEX2PN (816 +/- 607 pg/mL), and bioavailability was 54 +/- 40% and 73 +/- 43%, respectively. The highest plasma dexmedetomidine concentration was measured with DEXIIV (1,032 +/- 415 pg/mL) 5 minutes after injection. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that perineural injection of 0.5% ropivacaine in combination with dexmedetomidine (1 mu g/kg) for locoregional anesthesia in dogs seemed to balance the benefit of prolonging sensory nerve blockade while minimizing adverse effects.