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Peribulbar block with neosaxitoxin as an alternative to bupivacaine for perioperative pain management in dogs undergoing reconstructive keratoplasty


The aim of this study is to compare perioperative analgesic effects of peribulbar anesthesia with neosaxitoxin or bupivacaine in dogs. Twenty-four dogs diagnosed with deep corneal ulcer undergoing reconstructive keratoplasty, will be included in the study. The dogs will be premedicated with intramuscular (IM) dexmedetomidine (2 µg/kg) combined with methadone (0.3 mg/kg). Anesthesia will be induced with intravenous propofol (dose-effect) and maintained with isoflurane/O2. Immediately after tracheal intubation, the dogs will be randomly assigned to receive either peribulbar block with neosaxitoxin (3.5 µg, NeoSTX group, n = 12) or 0.5% bupivacaine (0.2 mL/kg; Bupi group, n =12). Neosaxitoxin will be diluted in 0.9% saline solution to achieve a final volume of 0.2 mL/kg. Intraoperatively, cardiorespiratory variables and end-tidal isoflurane concentration (FE´ISO) will be monitored. Fentanyl (2.5 µg/kg) will be administered to control cardiovascular responses to surgical stimulation The degree of analgesia and sedation will be measured using subjective pain scores, before premedication (baseline), 1, 2, 4, 8, 12, 18 and 24 hours after extubation. Corneal sensitivity, pupilar diameter, pupillary light reflex and blepharospasm degree will be evaluated at baseline and at different time points after the peribulbar block. Rescue analgesia will be provided with IM methadone (0.3 mg/kg). Numerical data will be submitted to analysis of variance followed by Tukey's test for parametric measures, and Mann-Whitney and Friedman tests with post-Dunn test for nonparametric measures (p <0.05). (AU)

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