Brachycephalic Airway Obstruction Syndrome

Many disorders of the airway requiring diagnostic or surgical intervention are found in the brachycephalic breeds, which include the Bulldog, Pekingese, Shih Tzu, Chow Chow, Boston Terrier, Pug and, to a lesser extent, Mastiff, Staffordshire Bull Terrier, and Cavalier King Charles Spaniel. 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; on the other hand, 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 impeding airflow and making breathing difficult, especially when the animal is stressed or exercised in warm weather.

Brachycephalic Airway Obstruction Syndrome in dogs

Brachycephalic 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 require surgical correction. Brachycephalic dogs affected by Brachycephalic Airway Obstruction Syndrome (BAOS) have a much higher incidence of gastrointestinal tract problems. Surgical treatment of respiratory disease could improve the digestive clinical signs, and/or gastro-oesophageal medical treatment could improve the outcome for surgically treated brachycephalic dogs.2 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 chances of worsening of the disease.



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Brachycephalic airway obstruction can take several forms, such as overlong soft palate, tracheal hypoplasia, and laryngeal paralysis. The inherent anatomy of the brachycephalic skull contributes to the development of these signs. Collapsed nostrils and elongated soft palate are congenital defects, while eversion of laryngeal succules is acquired. The increased negative pressure created in 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 signs usually include reduced exercise tolerance, whistling-type or snoring-type noise, mouth breathing, snorting, rapid breathing, difficult breathing, cyanosis, and collapse. Affected dogs have difficulty filling the lungs, which may result in the swelling of the nasal passages and throat), further reducing airflow. Thus a vicious cycle supervenes. The impeded airflow prevents adequate heat loss through panting so, particularly in hot weather, body temperature increases.

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 breathing, it does not result in a completely normal airway. Furthermore, although technically simple to perform, upper airway surgeries can lead to the development of significant postoperative complications1.

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 flattened from front to back. The puppies fail to thrive and are poorly developed. Stenotic nares can be treated successfully by surgically enlarging the nasal openings, although not all dogs with stenotic nares require surgery. In some dogs, the cartilage firms up satisfactorily by six months of age.



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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 breathing and laryngeal collapse. An elongated palate is treated by surgically shortening the palate so that the edge opposes or slightly overlapse the epiglottis. Laryngeal succules are small mucosal pouches that project into the larynx. In long-standing upper airway obstruction the succules enlarge and turn out, 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.

References

  1. Mercurio A. Complications of upper airway surgery in companion animals.
  2. Poncet CM, Dupre GP, Freiche VG, Estrada MM, Poubanne YA, Bouvy BM. Prevalence of gastrointestinal tract lesions in 73 brachycephalic dogs with upper respiratory syndrome.



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