Evaluation of analgesia provided by the administration of epidural ketamine in dogs with a chemically induced synovitis

Abstract

Objective To determine if epidural ketamine provides analgesia in dogs with a chemically induced synovitis.Study design Prospective randomized experimental trial.Animals Thirty-two healthy, adult mongrel dogs (13–30 kg).Methods (Part I) Synovitis was induced in the right stifle of 16 dogs and allowed to develop for 12 hours. Epidural injection at the lumbosacral space of either ketamine (2 mg kg−1; n = 8) or placebo (n = 8) was performed. Limb use and pain were measured using a force platform and numerical rating scale (NRS). Assessments were performed before and at 12, 14, 16, 18, 20, and 24 hours after the induction of synovitis. (Part II) Epidural injection of either ketamine (n = 8) or placebo (n = 8) was performed immediately before the induction of synovitis. Analgesia was assessed as in Part I. Assessments occurred before and at 2, 4, 6, 8, and 12 hours after the induction of synovitis.Results (Part I) Vertical ground reaction forces (VGRF) significantly decreased and NRS scores of total pain significantly increased after the induction of synovitis in all dogs (p < 0.05). No significant differences in VGRF or NRS scores were measured between treatment groups at any assessment period. (Part II) Dogs that received ketamine had significantly lower NRS scores 2 hours after treatment (p < 0.05). NRS scores did not differ between groups at any other evaluation. VGRF did not differ significantly between treatment groups at any assessment period.Conclusion Epidural ketamine at a dose of 2 mg kg−1 administered after the development of synovitis does not provide significant levels of analgesia. Administration of ketamine before the induction of synovitis significantly decreased the NRS score 2 hours post-induction.Clinical relevance Administration of epidural ketamine before tissue injury may provide analgesia of short duration in dogs.