The Analgesic Effects of Epidural Ketamine in Dogs With a Chemically Induced Synovitis: A Comparison Between Pre - or Post - Injury Administration
Hamilton, Stephanie Marie
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The objective of this study was to determine if administering epidural ketamine before or after the induction of a sodium urate crystal synovitis provides analgesia in dogs. In Part I, sixteen dogs were anesthetized with propofol (4 mg kg-1 intravenously). A sodium urate crystal synovitis was induced in the right stifle and allowed to develop for 12 hours. These dogs were again anesthetized with propofol and an epidural injection at the lumbosacral space of either ketamine (2 mg kg-1) or placebo (saline containing not more than 0.1 mg ml-1 benzethonium chloride) was performed. Analgesia was measured with a force platform and a numerical rating scale (NRS). Assessments were performed before and at 12, 14, 16, 18, 20 and 24 hours after the induction of synovitis. Vertical ground reaction forces were significantly decreased and numerical rating scale scores of total pain were significantly increased after the induction of synovitis in all dogs (p<0.05). No significant differences in ground reaction forces or total pain scores were measured between the ketamine and the control groups at any assessment period. In Part II, synovitis was induced in the right stifle as described in Part I. Epidural injections at the lumbosacral space followed immediately. Analgesia was assessed at 2, 4, 6, 8, and 12 hours after the epidural injection and the induction of synovitis. Dogs that received ketamine had significantly lower NRS scores two hours after treatment (p < 0.05). NRS scores did not differ between the two treatment groups at any other evaluation. Vertical ground reaction forces did not significantly differ between treatment groups at any assessment period. Results of this study indicate that ketamine, when administered epidurally at a dose of 2 mg kg-1 after the induction of a chemical synovitis, does not provide a significant level of analgesia. However, administration of ketamine immediately before the induction of synovitis resulted in a significantly decreased subjective pain score at two hours, but not at later evaluation periods.
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