The post-operative analgesic effects of ketamine after canine ovariohysterectomy--a comparison between pre- or post-operative administration.

Thirty-six female dogs undergoing ovariohysterectomy were randomly allocated into three groups in this assessor-blinded study. The control group received no ketamine, the preketamine group were given ketamine (2.5 mg kg(-1)i.m.) at anaesthetic induction (in addition to the induction agents), the post-ketamine group received ketamine (2.5 mg kg(-1)i.m.) at extubation. Mechanical nociceptive thresholds and visual analogue scale (VAS) scores were measured before premedication and post-operatively at 20 minutes, 1, 2, 4, 8 and 18 hours after extubation. Dogs in the control group required more rescue analgesics than those in the other two groups (significantly more than the preketamine group), they also had consistently higher VAS pain scores throughout the post-operative period. Administration of ketamine post-operatively delayed the onset of post-operative wound hyperalgesia; dogs in the control group had the greatest amount of post-operative wound hyperalgesia. A single subanaesthetic dose of ketamine provided effective but short acting analgesia and preoperative administration may confer some benefits over administration post-operatively.