Pain management with peribulbar anesthesia versus retrobulbar anesthesia in a cat undergoing bilateral enucleation

A 14 year old, 6 kg, domestic short hair, spayed female cat was presented with bilateral uveitis, iris bombe, glaucoma, and blindness. Conventional treatment did not resolve the glaucoma, thus a bilateral enucleation was scheduled. Methadone was administered intravenously for anesthetic premedication, and anesthesia was induced with etomidate and midazolam given intravenously to effect, and maintained with isoflurane in 100% oxygen. Atropine was administered intramuscularly after induction. Preoperatively, a peribulbar anesthesia with 9 mg of bupivacaine 0.5% diluted with 1.8 mL of saline 0.9% was performed on the left eye, and a retrobulbar anesthesia with 2.5 mg of bupivacaine 0.5% diluted with 0.5 mL of saline 0.9% was performed on the right eye. During enucleation of the left eye, the cat did not move, and had low isoflurane vaporizer settings; however, during surgery of the right eye, the cat moved several times, and required higher isoflurane vaporizer settings, and additional methadone. After extubation the cat did not react to manual pressure on the left eye incision, but moved its head when the right eye incision was touched. Postoperative analgesia was provided with methadone. The cat recovered uneventfully, and had an increase in appetite several hours after surgery. The administration of peribulbar anesthesia was more likely to decrease inhalant requirements, and provide postoperative analgesia of the incision site. Additional research is indicated to investigate whether peribulbar anesthesia is preferable in cases of feline enucleation.