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Special Anesthetic Considerations for the Norwich Terrier

Clinician's Brief (Capsule)

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Four characteristics may be seen in brachycephalic syndrome: Stenotic nares, elongated soft palate, everted laryngeal saccules, and tracheal hypoplasia. Typical phenotype includes a severely shortened muzzle, short and wide head, prognathism, and prominent wide-set eyes. Although the Norwich terrier does not share these phenotypic traits, breeders and clients have expressed concern regarding reported breathing difficulty in the breed. This study evaluated 16 Norwich terriers: 12 presented with respiratory noise or apparent respiratory difficulty, and 4 were clinically normal. Standard physical examination included subjective assessment of size of the external nares; evaluation of nasal airflow; soft palate palpation; and auscultation of the larynx, trachea, and lungs. Laryngoscopy was performed to visualize the tonsils, soft palate length, laryngeal saccules, laryngeal structure, and laryngeal function. Additional imaging studies were performed in some of the dogs. The study revealed redundant supraarytenoid folds and laryngeal narrowing in 9 of the dogs presented with respiratory signs and 3 of the dogs that were clinically normal. This required a smaller endotracheal tube than would be used in dogs of comparable weight and could result in postanesthetic recovery complications related to airway obstruction. In contrast to other breeds with brachycephalic syndrome that exhibit changes in the nares or soft palate, Norwich terriers appear to have obstruction at the level of the larynx, with narrowing caudal to the vocal fold that decreases luminal diameter. This is presumed to result in airflow obstruction, trauma to upstream tissues, and severe redundancy of supraarytenoid tissue with further airflow obstruction.

Commentary

Norwich terriers may require their own anesthetic protocol considerations, such as drugs that reduce apnea, antiinflammatory medications (eg, steroids) to alleviate postintubation tracheal trauma, and smaller endotracheal tubes. Attention may also need to be placed upon ensuring the dog is extubated after full recovery (ie, in sternal recumbency and chewing the tube). This study also emphasized the importance of not assuming lack of risk for obstruction based on a normal physical examination in a breed with heritable predisposition for airway obstruction.—Heather Troyer, DVM, DABVP, CVA

Source

Upper airway obstruction in Norwich terriers: 16 cases. Johnson LR, Mayhew PD, Steffey MA, et al. JVIM 27:1409-1415, 2013.

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