Brachycephalic Obstructive Airway Syndrome (BOAS)

Brachycephalic Obstructive Airway Syndrome (BOAS) is a debilitating respiratory syndrome that is caused by upper airway abnormalities. This syndrome commonly affects brachycephalic dog breeds such as the English bulldog, pug, French bulldog, Boston terrier, Boxer, Pekingese, shih tzu, and Chinese Sharpei, just to name a few. A brachycephalic breed has a shortened muzzle due to many years of inbreeding for these particular facial features. As a result, the skull bones of these dogs are compressed such that the dog has a more flattened facial conformation compared to other dogs (see image below).  

Photo credits: Imgur

What are the problems associated with BOAS?

The anatomical variations of the skull bones result in abnormalities of the upper respiratory system. Overall, there can be varying degrees of breathing difficulties depending on the extent of the abnormalities. Furthermore, the severity of symptoms may increase as the dog ages. 

BOAS symptoms include:

  • Noisy breathing (e.g. snoring, wheezing, snorting)
  • Reduced or inability to exercise
  • Gagging when swallowing food or water
  • Labored breathing
  • Open-mouth breathing
  • Bluish colouration (instead of pink) of the gums
  • Collapse

What causes BOAS?

As mentioned, the abnormal anatomical structure of the brachycephalic breed causes deformities in the upper airway, causing obstructions in breathing. These airway obstructions include:

  • Stenotic nares – congenitally small nostrils that may also collapse as the dog inhales.
  • An elongated soft palate – this obstructs airflow into the larynx.
  • Everted laryngeal saccules – a tissue near the vocal cords pulled inward during inhalation and can block airflow.
  • Hypoplastic trachea – some dogs may have a windpipe (trachea) that is proportionally too narrow.
Abnormal anatomical structures in the upper airway tract of brachycephalic breeds

Other structural changes that can contribute to airflow obstruction include:

  • Laryngeal collapse
  • Large tongue
  • Enlarged or everted tonsils

Over time, the condition worsens due to inflammation of the tissues around the throat as the dog has to work hard to breathe. With the inflammation and swelling, further airflow obstruction occurs.

How is BOAS diagnosed?

Most dogs are diagnosed between one and four years of age. The diagnosis is made based on a combination of factors including the breed of dog, respiratory distress symptoms, and physical examination findings. Stenotic nares can be observed on physical examination. Further evaluation requires the dog to be lightly anaesthetized for the veterinarian to assess the soft palate and laryngeal saccules. The diameter of the trachea can be assessed by taking X-rays of the neck and chest. Advanced testing can also be carried out, such as a CT scan of the upper airway.  

How is BOAS treated?

Mild cases can be treated conservatively with the following:

  • Maintenance of a healthy weight
  • Minimum excitement
  • Avoidance of excessive heat and humidity
  • Controlled activity 
  • Minimum stress
  • Using a harness instead of a neck collar

More severe cases, however, will require surgical correction. Earlier intervention at a younger age has been proven to have better outcomes. If you are concerned about BOAS in your dog, please consider a consultation with a veterinary surgeon*. Surgical corrections include:

  • Widening of stenotic nares by removing a small wedge of tissue to make the opening larger.  
  • Shortening of the elongated soft palate.
  • Removal of everted saccules.
Left: stenotic nares before surgical correction; right: normal nostrils after surgical correction (surgery done at Yee Vet)

There are anaesthetic risks associated with these patients due to their poorly constructed airways. Risks of complications include mortality associated with surgery. Surgical risks include bleeding, swelling and aspiration pneumonia.

BOAS can become an emergency situation. If your dog is experiencing a respiratory crisis, immediate transport to your veterinarian or nearest emergency clinic is crucial.

Other conditions associated with BOAS

  • Laryngeal collapse can occur as a result of chronic upper airway obstruction
  • Gastrointestinal disorders such as hiatal hernia and gastroesophageal reflux (these are usually improved following treatment for BOAS)
  • Aspiration pneumonia
  • Heart disease and lung disease

What are the possible outcomes?

Dogs with milder cases of BOAS can have normal life expectancies. Early surgical intervention (dogs under 2 years of age) leads to better outcomes such as reduced breathing noises, reduced risk of heat stroke, choking, aspiration pneumonia, and death due to insufficient oxygen. Dogs with laryngeal collapse, however, have less favourable outcomes, despite surgery.

Prevention of BOAS

As this is a genetic condition, brachycephalic dogs that have difficulty breathing and require surgical therapy or have a hypoplastic trachea should not be considered for breeding. 



Dr Yee Jia Yin

Yee Veterinary Clinic & Surgery

*BOAS correction surgery services are available at two of our branches: Yee Veterinary Clinic & Surgery and Kota Damansara Veterinary Clinic & Surgery