Ultrasound-guided coronoid approach to the trigeminal nerve block in a dog undergoing orbital exenteration.

Abstract

An ultrasound-guided trigeminal nerve block using a coronoid approach was performed in a male neutered Jack Russell Terrier, aged 12 years, undergoing orbital exenteration for a retrobulbar mass. The previously reported temporal approach for this block was contraindicated as the location of the mass risked intersecting the tumour with the needle. With the dog anaesthetized and in left lateral recumbency, a microconvex transducer was placed caudal to the orbital ligament to obtain a transverse view of the pterygopalatine fossa. The angle of the probe was adjusted until the frontal bone and sphenoid complex could be visualized, along with the coronoid process of the mandible. Colour Doppler identified the location of the maxillary artery exiting the skull. A 22 gauge, 38 mm, spinal needle was inserted using an in-plane technique until the tip was near the artery. After negative aspiration, 1.35 mL of 0.75% ropivacaine was injected, with anechoic fluid observed during injection along the fascial plane and around the artery. During surgery, noninvasive arterial blood pressure remained within 20% of baseline values, whereas heart rate (HR) increased from 95 to 118 beats minute, exceeding the 20% threshold. A low dose of intravenous methadone (0.07 mg kg) was administered without effect, and HR normalized following intravenous fluid infusion, consistent with a response to vasodilation rather than nociception. A multimodal analgesic plan (methadone, paracetamol and meloxicam) was implemented and continued postoperatively. Postoperative pain was assessed every 4 hours using the Short Form Glasgow Composite Measure Pain Scale, with scores remaining below the rescue threshold throughout the postoperative period. This case suggests that the coronoid approach to the trigeminal nerve block is feasible and may be effective as part of a multimodal analgesic approach. Further studies are warranted to evaluate its safety and efficacy in dogs undergoing craniofacial surgery.