Retrobulbar block as an analgesic strategy for enucleation in a horse: case report

Resumo

Ophthalmic surgeries in horses frequently require general anesthesia, which is associated with important anesthetic risks in this species.  In this context, locoregional anesthesia techniques are essential to provide effective analgesia and reduce general anesthetic requirements, minimizing adverse effects. The use of ultrasonography has increased the safety and precision of these blocks when compared with blind techniques. Thus, the present report describes the use of an ultrasound-guided retrobulbar block in a 7-year-old Mangalarga horse weighing 400 kg that underwent enucleation. The animal presented a severe lesion in the right eye associated with mucopurulent discharge. Ophthalmic examination revealed corneal perforation with iris prolapse and uveitis, and transpalpebral enucleation was indicated. The anesthetic protocol included detomidine (10 µg/kg IV) as premedication, induction with ketamine (2.2 mg/kg IV), diazepam (0.05 mg/kg IV), and glyceryl guaiacol ether (50 mg/kg IV). Anesthesia was maintained with isoflurane (1–2%) associated with continuous lidocaine infusion (50 µg/kg/h IV). As part of balanced anesthesia, an ultrasound-guided retrobulbar block was performed, allowing visualization of orbital structures, adequate needle positioning, and local anesthetic spread within the intraconal space. Additional eyelid blocks were also performed. Physiological parameters remained stable throughout the procedure, except for one brief episode of anesthetic plane superficialization, which was promptly corrected with anesthetic adjustments and supplemental ketamine administration. Anesthetic recovery was uneventful, and the horse returned to a quadrupedal position approximately 40 minutes after the end of anesthesia. The retrobulbar block promotes analgesia and akinesia of the ocular globe through desensitization of the nerves located within the intraconal space. The use of ultrasonography increases the precision of the technique and reduces complications associated with the method. In the present report, hemodynamic stability, absence of evident nociceptive signs during most of the procedure, and satisfactory recovery suggest that ultrasound-guided retrobulbar block was an effective multimodal analgesic strategy in a horse undergoing enucleation.