Comparison of peribulbar anesthesia with neosaxitoxin or bupivacaine in dogs undergoing reconstructive keratoplasty.

BACKGROUND

This study compared the analgesic efficacy of peribulbar anesthesia using neosaxitoxin versus bupivacaine in dogs undergoing reconstructive keratoplasty.

METHODS

Of 28 dogs, four were excluded for not meeting the inclusion criteria. The anesthetic protocol included dexmedetomidine and methadone, propofol and isoflurane. Immediately after intubation, 24 dogs were randomly assigned (12 per group) to receive peribulbar block with either neosaxitoxin (3.5µg; NeoSTX group) or 0.5% bupivacaine (0.2mL/kg, Bupi group). Intraoperatively, cardiopulmonary variables and end-tidal isoflurane concentration (FE'ISO) were recorded at predefined time points. Pain, corneal esthesiometry, blepharospasm, and sedation were assessed preoperatively and up to 24hours post-extubation. Methadone was administered as rescue analgesia. The duration of analgesia, defined as the interval between block administration and the first rescue analgesia, was also recorded.

RESULTS

Cardiopulmonary parameters, blepharospasm, duration of analgesia and sedation scores did not differ between treatments. The area under the curve (AUC) of Fe´ISO and esthesiometry were lower in the NeoSTX group compared to the Bupi group (P = 0.004; P = 0.009, respectively). Pain was lower in the Bupi group at 12hours post-extubation compared with the NeoSTX group (P = 0.012). Methadone was required in 4/12 dogs in each group, administered at 4-6hours post-extubation in the Bupi group and at 12-18hours in the NeoSTX group.

CONCLUSION

In conclusion, at the dose and concentrations used in this study, peribulbar NeoSTX was associated with lower isoflurane and corneal esthesiometry AUCs, but did not provide additional postoperative analgesic benefit compared with bupivacaine.