Preliminary evaluation of pain behaviors following neutering in dogs: effect of acepromazine dose

Abstract

The purpose of this study was to determine an acceptable dose of acepromazine (ACE) to be used in a large-scale study of pain behaviors following neutering in dogs. The objectives were to find a dose of ACE that was high enough to provide some sedation to facilitate induction and recovery from anesthesia without causing prolonged recovery that would prevent evaluation of postoperative pain behaviors, and to gain experience with the pain scales to be used in the study. Sixty dogs (33 males, 27 females), 1.36 ± 0.16 years of age and weighing 14.3 ± 1.29 kg (mean ± SEM) were the subjects of this study. Dogs were pre-medicated with glycopyrrolate (0.02 mg kg−1 SQ) and randomly administered ACE at 0.025 mg kg−1 SQ (LOW) or 0.05 mg kg−1 SQ (HIGH). Approximately 30 minutes later, anesthesia was induced with diazepam (0.56 mg kg−1 IV) and ketamine (11.1 mg kg−1 IV) and maintained with isoflurane. The pain behaviors were evaluated for the first 4 hours of recovery using the University of Melbourne Pain Scale (UMPS) and Glasgow Composite Pain Tool by an observer unaware of ACE dose. Treatment groups were compared using an unpaired t-test, with p < 0.05 considered significant. Duration of anesthesia (25.4 ± 1.5 minutes), duration of surgery (12.4 ± 1 minutes), and length of incision (2.7 ± 0.14 cm) were not different between treatment groups. Duration of surgery for females (14.2 ± 1.1 minutes) was not different than males (11 ± 1.6 minutes). Cumulative pain scores (UMPS) over the 4-h observation period for LOW (49.1 ± 1.9) and HIGH (49.7 ± 2) dose ACE were not significantly different. The results of this study suggest that ACE at 0.025 mg kg−1 SQ affects pain behaviors similarly to ACE at 0.05 mg kg−1 SQ. Recognizing that the ACE can induce profound sedative effects when combined with opioid analgesics, the low dose of ACE was chosen for the subsequent analgesic study. In this preliminary study, the UMPS had the advantage of providing a numeric value for comparison of pain scores, whereas the Glasgow Composite Pain Tool was easier to use, requiring less observer interpretation of behaviors.