A comparative analysis of opioid-free and opioid-sparing anaesthesia techniques for laparoscopic ovariectomy in healthy dogs

Abstract

Objective: To compare the perioperative analgesic effects of an opioid-free (OFA) and an opioid-sparing (OSA) anaesthetic protocol in dogs undergoing laparoscopic ovariectomy.

Study design: Prospective, randomized, blinded, clinical trial.

Animals: A group of 28 client-owned dogs.

Methods: Dogs were allocated to one of two groups. The OFA group was administered intramuscular (IM) dexmedetomidine 5 μg kg^-1 and ketamine 1 mg kg^-1, followed by two intraoperative constant rate infusions (CRIs) of dexmedetomidine (3 μg kg^-1 hour^-1) and lidocaine (1 mg kg^-1 loading dose, 2 mg kg^-1 hour^-1). The OSA group was administered IM dexmedetomidine 5 μg kg^-1, ketamine 1 mg kg^-1 and methadone 0.2 mg kg^-1, followed by two intraoperative saline CRIs. In both groups, anaesthesia was induced with intravenous (IV) propofol 2 mg kg^-1 and diazepam 0.2 mg kg^-1 and maintained with isoflurane. Rescue dexmedetomidine (0.5 μg kg^-1) was administered IV if there was a 20% increase in cardiovascular variables compared with pre-stimulation values. Ketorolac (0.5 mg kg^-1) was administered IV when the surgery ended. Postoperative analgesia was evaluated using the Short Form-Glasgow Composite Measure Pain Scale and methadone (0.2 mg kg^-1) was administered IM if the pain score was ≥ 6/24. Statistical analysis included mixed analysis of variance, Chi-square test and Mann-Whitney U test.

Results: There were no significant differences in the intraoperative monitored variables between groups. The OFA group showed a significantly lower intraoperative rescue analgesia requirement (p = 0.016) and lower postoperative pain scores at 3 (p =0.001) and 6 (p < 0.001) hours. No dogs were administered rescue methadone postoperatively.

Conclusions and clinical relevance: Although both groups achieved acceptable postoperative pain scores with no need for further intervention, the analgesic efficacy of the OFA protocol was significantly superior to that of the OSA protocol presented and was associated with a lower intraoperative rescue analgesia requirement and early postoperative pain scores.

Keywords: analgesia; dexmedetomidine; lidocaine; opioid-free anaesthesia.