Anatomical localisation of the maxillary nerve with the use of computed tomography to aid nerve block placement in dogs

Background: The maxillary block is a commonly used anaesthetic technique in dogs; however, no universal recommendations for the best method to perform this block exist. Differences between using this block in brachycephalic and non-brachycephalic breeds have not been examined. This study compared the position of the maxillary nerve using CT in brachycephalic and non-brachycephalic dogs. Methods: Forty CT images of the heads of dogs of varying conformation were analysed. The distances and angles to the maxillary nerve from the injection site within the oral cavity were measured. If present in the same plane, the distance to the eye was measured. Measurements of jaw width and length were taken to ascertain if they correlated to the distance to the maxillary nerve from the oral cavity. Results: There was no difference in angle between brachycephalic and non-brachycephalic dogs; however, the distance between nerve and injection point in brachycephalic dogs was generally greater. A regression equation relating maxillary nerve depth to jaw width was found. The eye was more likely to be in the plane of injection if the dog was non-brachycephalic. Conclusion: The discovered relationship between jaw width and maxillary nerve depth may allow more accurate injections to be made.