A comparison of epidural analgesia provided by bupivacaine alone, bupivacaine plus morphine, or bupivacaine plus dexmedetomidine for pelvic orthopedic surgery in dogs

Objective To compare the analgesic efficacy of bupivacaine, bupivacaine+morphine, or bupivacaine+dexmedetomidine administered epidurally in dogs undergoing pelvic limb orthopedic surgery. Study design Prospective, randomized, double blinded clinical trial. Animals Sixty dogs weighing (mean +/- SD) 35 +/- 15.7kg, aged 5 +/- 3years. Methods Dogs were assigned to receive a lumbosacral epidural containing bupivacaine (B) 0.5%, 1mgkg(-1); B, bupivacaine 0.5%, 1mgkg(-1)+morphine 1%, 0.1mgkg(-1); B+M, or bupivacaine 0.5%, 1mgkg(-1)+dexmedetomidine 0.05%, 4gkg(-1); B+D. The anesthetic protocol was standardized. The median expired isoflurane concentration (EIso) and requirement for additional induction agent preventing purposeful movement were recorded. Pain was scored using visual analog (VAS) and modified University of Melbourne (UMPS) pain scales. Sedation was assessed using a 0-4 scale. All parameters were recorded preoperatively, and at extubation (t=0), then at 1, 2, 4, 8, 12, 16, and 20-24hours. Hydromorphone was administered postoperatively to patients with a VAS35 and/or UMPS9. Time to first voluntary urination and first motor activity were recorded. Results ostoperatively, B+D had a lower UMPS pain score than B at t=1hour (p=0.013), but not compared to B+M. The B+D group had a shorter time to urination (p=0.0131) and a longer time for return of motor function (p=0.0068). There were no other differences between the treatments. Conclusion and clinical relevance Epidurally administered B, B+M, or B+D in dogs all provided acceptable analgesia to manage post-operative orthopedic pelvic limb pain. Epidural administration of B+D is an effective alternative to the analgesia provided by B or B+M, but is associated with increased time to return of motor function. The direct neurotoxic effects of epidural dexmedetomidine have not been fully tested.