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

Objective To compare the peri-operative 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 into one of two groups. The OFA group received intramuscular (IM) dexmedetomidine 5 μg kg-1 and ketamine 1 mg kg-1, followed by two intra-operative 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 received IM dexmedetomidine 5 μg kg-1, ketamine 1 mg kg-1 and methadone 0.2 mg kg-1, followed by two intra-operative 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 to pre-stimulation values. Ketorolac (0.5 mg kg-1) was administered IV when the surgery ended. Post-operative analgesia was evaluated using the Short Form-Glasgow Composite Measure Pain Scale and IM methadone (0.2 mg kg-1) was administered 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 intra-operative monitored variables between groups. The OFA group showed a significantly lower intra-operative rescue analgesia requirement (p = 0.016) and lower post-operative pain scores at 3 (p =0.001) and 6 (p < 0.001) hours. No dogs received rescue methadone post-operatively. Conclusions and clinical relevance Although both groups achieved acceptable post-operative pain scores with no need for further intervention, the analgesic efficacy of OFA was significantly superior to that of the OSA protocol presented and was associated with a lower intra-operative rescue analgesia requirement and early post-operative pain scores.