Adnexal Surgery

The first decision in equine adnexal surgery is whether to perform the procedure as a standing surgery or to use general anaesthesia. Knowledge of regional motor and sensory nerve blocks and the technique for performing a retrobulbar nerve block are essential. Regional anaesthesia of the auriculopalpebral branch of CN VII and the supraorbital (frontal) branch of CN V provide akinesia and anaesthesia of the superior eyelid, respectively. The auriculopalpebral nerve is blocked by injection at the intersection of a line parallel to the caudal aspect of the ramus of the mandible and a line parallel to the dorsal aspect of the zygomatic arch. Using a 25 gauge 5/8 inch needle 3–5 ml of mepivacaine HCl or similar agent is injected. The supraorbital nerve is blocked as it emerges from the supraorbital foramen of the frontal bone. This foramen is palpated, a 25 gauge 5/8 inch needle is inserted into the foramen and 2 ml of mepivacaine HCl is injected, another 1–2 ml is infiltrated subcutaneously as the needle is removed. Additional sensory nerves, which may be occasionally anaesthetised, include the infratrochlear, lacrimal and zygomatic branches of CN V. Alternatively, local infiltration of anaesthetic can be used to provide anaesthesia of a specific area such as a region of the eyelid or third eyelid. A retrobulbar block uses a 75–100 mm spinal needle inserted posterior to the arch of the frontal bone and directed ventrally. The needle is inserted intraconally and 7–10 cc of mepivicaine is injected. As the needle is advanced, it contacts the dorsal muscle cone and the globe will deviate dorsally. The needle is then advanced through the dorsal muscle cone to the intraconal space. The surgeon should allow 10–15 min for effect. Following a retrobulbar block the head should be kept elevated for 1–2 h to prevent dependant conjunctival swelling. Topical proparacaine 0.5% ophthalmic is applied as a topical anaesthetic. If haemorrhage is a concern, topical 1:10,000 epinephrine may be applied as a vasoconstrictor. [...]