Analgesic effects of a retrobulbar block with 0.75% ropivacaine in dogs undergoing enucleation

Abstract Objective To assess the analgesic effects of a retrobulbar block with ropivacaine in dogs undergoing enucleation. Study design Prospective, randomized, masked placebo-controlled trial. Animals A total of 23 client-owned dogs. Methods Dogs were randomized to be administered a preoperative inferior-temporal palpebral retrobulbar injection of either ropivacaine 0.75% (1 mL 10 kg−1) or equivalent volume of 0.9% saline (control). Intraoperative variables recorded to detect a response to noxious stimuli included heart rate (HR) and mean arterial pressure (MAP). Three observers assessed and recorded pain using a numerical rating pain scale and visual analog scale (VAS) before anesthesia (baseline) and postoperatively at 0, 0.5, 1, 2, 3, 4, 5, 6 and 24 hours after extubation. Rescue analgesia was administered if intraoperative HR or MAP increased by ≥ 20% from the previously recorded surgical time point, average postoperative pain scores totaled ≥ 9/20, scored ≥ 3/4 in any 1 category with VAS ≥ 35/100, or if VAS was ≥ 35/100 with a palpation score > 0/4. Results Intraoperatively, there was no significant difference in HR or MAP between groups. Rescue analgesia was administered intraoperatively to four of 12 saline dogs and one of 12 ropivacaine dogs, and postoperatively to five and seven dogs administered saline or ropivacaine, respectively, with no significant difference between groups. VAS scores were significantly lower in ropivacaine dogs at extubation (p = 0.02), but not at other postoperative time points. Adverse events were not observed in either group. Conclusions and clinical relevance Preoperative retrobulbar 0.75% ropivacaine injection (1 mL 10 kg−1) provided analgesia in dogs following enucleation at extubation; however, intraoperative and postoperative pain control did not differ from a placebo injection with saline. Lack of differences between groups may have been influenced by sample size limitations.