Possible Brainstem Anaesthesia in a Cat after Ultrasound-Guided Retrobulbar Block

SIMPLE SUMMARY: Very commonly, local anaesthetic is deposited behind the eye to provide analgesia in animals that have an eye removed. In humans, this technique has been associated with complications like seizures and apnoea, while this has been reported only once, so far, in a cat. We present a case report of acute respiratory arrest during anaesthesia that occurred after local anaesthetic was administered behind the eye of a 13-year-old Siamese cat under ultrasound guidance. The cat stopped breathing almost instantly, and its heart rate and blood pressure increased significantly. The high blood pressure resolved quite quickly, but the cat very quickly developed hypotension and bradycardia, which were difficult to treat. Spontaneous breathing returned 20 min after the end of anaesthesia. The cat recovered well, but the contralateral eye did not respond to light and vision and seemed to be impaired. The spread of the local anaesthetic in the brain of the cat was suspected, based on the similarities with other reported cases, mainly in humans. The following day, the symptoms improved but were not completely resolved. One week later, during a follow-up examination, there were no concerns. The addition of this case report to the literature will help to raise awareness regarding this rare but potentially life-threatening complication. ABSTRACT: A 13-year-old neutered, blue-eyed female Siamese cat with a bodyweight of 4.8 kg was admitted for enucleation of the right eye. An ultrasound guided retrobulbar block with 1 mL of ropivacaine was performed under general anaesthesia. When the tip of the needle was visualised inside the intraconal space, negative aspiration of the syringe before injection and no obvious resistance during injection were confirmed. Instantly, after ropivacaine was administered, the cat became apnoeic, and its heart rate and the blood pressure increased significantly for a short period of time. During surgery, the cat needed cardiovascular support to maintain blood pressure and was under continuous mechanical ventilation. Spontaneous breathing returned 20 min after the end of anaesthesia. Brainstem anaesthesia was suspected, and after recovery, the contralateral eye was examined. A reduced menace response, horizontal nystagmus, mydriasis, and absence of the pupillary light reflex were present. The following day, mydriasis was still present, but the cat was visual and was discharged. The inadvertent intra-arterial injection of ropivacaine was suspected to be the cause of the spread into the brainstem. To the current authors’ knowledge, possible brainstem anaesthesia has only been reported in a cat 5 min after a retrobulbar block but never instantly.