Brachycephalic airway syndrome, Part 1: Correcting stenotic nares
EDITOR'S NOTE: Surgery STAT is a collaborative column between the American College of Veterinary Surgeons (ACVS) and DVM Newsmagazine.
Brachycephalic airway syndrome is described in dogs and cats that have brachycephalic conformation (a short, wide head). The primary components of the syndrome are stenotic nares, an elongated soft palate and a hypoplastic trachea (most often seen in English bulldogs). All these features can be present, or the presence and severity of each component can vary. The result is altered airway pressures.
Syndrome effectsThe smaller breathing lumens make for an increased respiratory effort, which is most apparent on inspiration. Fluid (or air) flow through a tube is described by Poiseuille's law that states that, in regard to the radius of a tube's lumen, flow is directly related to the radius raised to the fourth power. So small changes in airway size create vast changes in flow—especially in small patients with small airways. Over time, the increased work of breathing causes the secondary components of the syndrome—eversion of the laryngeal saccules and laryngeal collapse.
The increased resistance to airway pressure creates more work for the patient to move air in and out of its lungs. This creates problems during exertion or when exposed to high ambient temperatures when panting is needed to cool the body. These scenarios can create an obstructive airway crisis, hyperthermia or both. As the disease progresses and secondary changes occur, a crisis can occur with minimal stress or exertion. Chronic hypoxia creates pulmonary vasoconstriction and eventually pulmonary hypertension.
Commonly affected breeds are English bulldogs, French bulldogs, pugs, Boston Terriers, Pekingese, Pomeranians, Shih Tzus and boxers. Hypoplasia of the trachea is most common in English bulldogs and is likely responsible for a worse prognosis in this breed.
Most surgeons think that to prevent the development of the secondary components of brachycephalic airway syndrome, the patients should undergo surgery at a young age since there are reports of dogs as young as 6 months of age with laryngeal collapse. Performing corrective procedures is often done concurrently with spaying or neutering. Each patient needs to be assessed on an individual basis to determine which procedures are indicated.
During the initial examination, evaluate patients for evidence of dyspnea. If open-mouth breathing alleviates dyspnea, the obstruction is likely nasal in origin. If dyspnea persists despite open-mouth breathing, soft palate and laryngeal lesions are likely present.
Preoxygenate animals before anesthetic induction. Examine the nares to determine whether the wing of the nostril impinges on the nares. First examine the nares while the patient is awake and then after anesthetic induction. During awake inspiration, animals with severely stenotic nares can be seen to suck the wing medially.
Upon induction, examine the palate and larynx. The length of the palate is deemed elongated when it comes past the level of epiglottis. Evaluate larynx function and look for evidence of collapse or dysfunction. Perform a thorough evaluation so that treatment can be tailored for each patient's needs.