Brachycephalic Airway Obstruction Syndrome

Many disorders of the airway requiring diagnostic or surgical intervention are found in the brachycephalic breeds. These include Bulldogs, Pekes, Shih Tzu, Chow Chow, Boston Terrier, and Pugs and, to a lesser extent, Mastiffs, Staffordshire Bull Terrier, and Cavalier King Charles spaniels. Although their faces may be appealing, brachycephalic dogs are susceptible to a variety of physical problems associated with the shape of their heads. During the process of genetically selecting for shorter faces, the bones of the muzzle have become shortened. However, the skin of the muzzle and the tissues of the mouth and throat did not shorten correspondingly. These tissues may be folded over or bunched up impedeing airflow and making breathing difficult, especially when the animal is stressed or exercised in warm weather. These dogs may also suffer damage to the cornea because of the protruding eyes or because their eyelids may not cover the cornea completely. Some of these problems can be corrected surgically.

Brachycephalic Airway Obstruction Syndrome is a complex condition that results from varying degrees of upper airways obstruction. Brachycephalic airway obstruction can take the form of several clinical entities, for example, overlong soft palate, tracheal hypoplasia and laryngeal paralysis. The signs usually include reduced exercise tolerance, whistling-type or snoring-type noise, mouth breathing, snorting, rapid breathing, difficult breathing, cyanosis (bluish discoloration of mucous membranes and gums), and collapse. The signs tend to get worse as the dog grows older.

This syndrome has many separate features. Some of these are primary initiating factors, which may be heritable or congenital and arise because of conformational abnormalities, and some are secondary and aquired later in life as a result of changes induced by the primary factors. The inherent anatomy of the brachycephalic skull contributes to the development of these signs. Such anatomic features include shortened and distorted nasopharynx (nose and throat), an overlong soft palate, narrowing of the nostrils and blockage of the passage of the air. Collapsed nostrils and elongated soft palate are congenital defects, while eversion of laryngeal succules is acquired. The increased negative pressure createdn the nose and throat, as a result of these obstructing structures, ultimately results in the distortion and collapse of the supporting cartilages of the larynx (the voice box, situated between the base of the tongue and the windpipe).

The early diagnosis and management of the primary factors is important in order to limit the development of the more serious and potentially fatal secondary disorders.

Surgical procedures are performed to remove, repair or bypass areas of obstruction, injury or disease. Long-term outcome after surgery is usually good, even in dogs with laryngeal collapse. However, dog owners should realize that even though corrective surgery may improve but does not result in a completely normal airway. The American Kennel Club will not allow a dog that has had a surgery for stenotic nares (collapsed nostrils) or elongated soft palate to compete.

Stenotic Nares (Collapsed Nostrils). In puppies with stenotic nares, the nasal openings are small and the nasal cartilage is soft and floppy causing the nostrils to collapse as the puppy breathes in. This produces varying degrees of airway obstruction, manifested by mouth breathing, noisy breathing, and occasionally nasal discharge. In severe cases, the chest is falttened fro front to back. The pups fail to thrive and are poorly developed. Stenotic nares can be treated successfullly by surgically enlarging the nasal openings. Not all dogs with stenotic nares require surgery. In some dogs the cartilage firms up satisfactorily by 6 months of age.

Elongated Soft Palate. The soft palate is a flap of mucosa that closes off the nasopharynx during swallowing. Normally, it touches or slightly overlaps the epiglottis (the cartilage in the throat which guards the entrance to the trachea (windpipe) and prevents fluid or food from entering it when one swallows). In dogs with elongated soft palate, the palate overlaps the epiglottis to a considerable degree, partially obstructing the airway during breathing. This is manifested by snorting, snoring, loud, harsh breathing, gurgling and gagging. The obstruction is worse with exercise. In time, stretched ligaments in the voice box lead to labored breating and laryngeal collapse. An elongated palate is treated by surgically shortening the palate so that the edge opposes or slightly overlapse the epiglottis.

Eversion of the Laryngeal Succules. Laryngeal succules are small mucosal pouches that project into the larynx. In long-standing upper airway obstruction the succules enlarge and turn out (eversion) , narrowing the airway further. Everted laryngeal succules often accompany elongated soft palate, and if present, they are usually removed. This operation is done at the same time as shortening of the palate.

Dogs with this condition have difficulty filling the lungs. This in turn may result in the swelling of the nasal passages and throat (airway edema), which furhter reduces airflow. Tus a vicious cycle supervenes. The impeded airflow prevents adequate heat loss through panting so, particularly in hot weather, hyperthermia can occur.

Dogs with this condition are at increased anesthetic risk and an even higher risk occurs with concurrent obesity, heart disease or aspiration pneumonia. Prognosis is better for dogs other than Bulldogs and for dogs that have concurrent correction of stenotic nares and elongated soft palate. Without surgery, prognosis is poor due to continued progression of acquired complications of the brachycephalic syndrome. Lifelong avoidance of risk factors is recommended to reduce chance of worsening of the disease.

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