Investigation of the interaction between buprenorphine and sufentanil during anaesthesia for ovariectomy in dogs

OBJECTIVE: To investigate the effect of buprenorphine pre-treatment on sufentanil requirements in female dogs undergoing ovariectomy. STUDY DESIGN: Randomized, 'blinded', prospective clinical study. ANIMALS: Thirty healthy female dogs referred for ovariectomy. MATERIALS AND METHODS: Dogs were randomly assigned to one of two pre-anaesthetic treatment groups. Those in the buprenorphine group (B) received buprenorphine 20 microg kg(-1) and acepromazine 0.03 mg kg(-1) IM. Control group (C) animals received an equal volume of NaCl 0.9% and acepromazine 0.03 mg kg(-1) IM. The anaesthetic technique was identical in both groups. Pre-anaesthetic medication consisted of intravenous (IV) sufentanil (1.0 microg kg(-1)) and midazolam (0.05 mg kg(-1)) and intramuscular atropine (0.03 mg kg(-1)). Anaesthesia was induced with propofol and maintained with a constant rate infusion of sufentanil (1.0 microg kg(-1) hour(-1)) and with oxygen-isoflurane. Ventilation was controlled mechanically. Ovariectomy was performed using a standard technique. Baseline heart rate (HR) and direct mean arterial blood pressure (MAP) were recorded before the first incision. Increases in HR and MAP of > or =20% over baseline and, or spontaneous ventilation were controlled using IV sufentanil (1.0 microg kg(-1)) repeated after 5 minutes if haemodynamic variables remained elevated or attempts at spontaneous ventilation persisted. Analysis of variance was used to determine group differences in mean and median HR and MAP and to compare the maximum HR and MAP attained during surgery. Poisson regression was used to compare the number of sufentanil injections required in both groups. RESULTS: Group B required 2.46 times more sufentanil injections (p = 0.00487) than dogs in group C to maintain haemodynamic stability and prevent spontaneous ventilation during surgery. Group B dogs also had a significantly higher (p = 0.034) marginal mean of the log maximum MAP (4.756 +/- 0.036) compared with group C (4.642 +/- 0.036). CONCLUSIONS: Pre-treatment with buprenorphine appears to negatively influence the antinociceptive efficacy of intra-operative sufentanil. CLINICAL RELEVANCE: Withholding buprenorphine therapy 6-8 hours before anaesthesia incorporating pure mu receptor agonists is probably advisable. Alternative methods of analgesia should be provided in this period.