End tidal halothane concentration and postoperative analgesia requirements in dogs: a comparison between intravenous oxymorphone and epidural bupivacaine alone and in combination with oxymorphone.

The purpose of this study was to compare the effects of epidural bupivacaine (BUP) and oxymorphone/bupivacaine (O/B) and intravenous (i.v.) oxymorphone (IVO) on halothane requirements during hind end surgery and postoperative analgesia in 24 dogs. Dogs were randomly assigned to treatment groups: O/B--oxymorphone (0.1 mg/kg) in 0.75% bupivacaine (1 mg/kg for a total volume of 0.2 ml/kg); BUP--0.5% bupivacaine (1 mg/kg for a total volume of 0.2 ml/kg) with i.v. oxymorphone (0.05 mg/kg) postoperatively; and IVO--oxymorphone (0.05 mg/kg) pre- and postoperatively. Heart rate (HR), respiratory rate, arterial blood pressure, end-tidal carbon dioxide and halothane, and arterial blood gases were recorded prior to treatment and every 15 minutes thereafter. Once surgery had begun, end-tidal halothane concentrations were decreased as low as possible while still maintaining a stable anesthetic plane. Data were analyzed using ANOVA with P < 0.05 considered significant. End-tidal halothane requirements did not differ significantly among treatments. Respiratory depression was increased and HR was decreased in the O/B and IVO groups. Postoperative analgesic requirements were significantly less in dogs receiving O/B.