Ultrasound-guided trigeminal nerve block with contrast-enhanced CT evaluation for extensive oncologic maxillofacial surgery in 7 dogs: a prospective case series

Abstract

Objectives

This study aimed to (1) describe an ultrasound-guided trigeminal nerve injection technique in client-owned dogs undergoing extensive oncologic maxillofacial surgery; (2) characterise the distribution of a local anaesthetic–contrast mixture using CT; and (3) confirm the absence of intracranial distribution of the injectate on CT images in clinical patients. A secondary objective was to describe intraoperative nociceptive responses under a multimodal anaesthetic protocol.

Materials and Methods

This prospective case series included seven client-owned dogs undergoing extensive oncologic maxillofacial surgery at a tertiary referral hospital. Unilateral or bilateral ultrasound-guided trigeminal nerve injections were implemented using a temporal approach. A combination of ropivacaine, dexmedetomidine and iohexol (1:15 contrast-to-local anaesthetic ratio) was injected at a total volume of 0.07 mL/kg per injection site. CT imaging was performed 5 to 10 minutes after injection to assess the injectate distribution and its proximity to the orbital fissure, rostral alar foramen and oval foramen. Intraoperative nociceptive responses were monitored by haemodynamic parameters and treated as required.

Results

Ten trigeminal nerve injections were performed (five left-sided, five right-sided; three dogs received bilateral injections). Sonoanatomical landmarks were consistently identified, and CT confirmed adequate injectate distribution within 5 mm of the targeted foramina in 8/10 injections. No intracranial distribution of contrast medium was observed. Intraoperative short-lived rescue analgesia was required in 4/7 dogs, consisting of a single bolus of fentanyl (1 μg/kg iv). No dogs required intraoperative redosing of rescue analgesia. No immediate or delayed adverse effects attributable to the injection technique or contrast administration were identified.

Clinical Significance

Ultrasound-guided trigeminal nerve block combined with CT imaging provides detailed, in vivo anatomical information regarding injectate distribution before extensive oncologic maxillofacial surgery in dogs. Within the limitations of this small case series, its incorporation into a multimodal anaesthetic protocol was associated with limited intraoperative nociceptive events and minimal use of additional systemic analgesic interventions.