Brachycephalic Obstructive Airway Syndrome (BOAS) In Dogs

Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS

Table Of Contents

- Intro
- Diagnosis
- Surgery
- Complications
- Outlook

Brachycephalic dogs are those with very short faces, such as English Bulldogs, Pugs, French Bulldogs, Boston Terriers, and some Shih Tzu’s. Obstructive airway syndrome describes the phenomenon of excess tissue at the back of the throat restricting breathing, and narrowed nares (nostril), which are commonly seen within these breeds. Cats and rabbits can also suffer with BOAS, but it more commonly requires treatment in our canine patients.

Brachycephalic dogs have shorter muzzles as a result of breeding practices. However, breed standards are trying to now focus on elongating the muzzles and improving their health. Often, the structures around the throat have not reduced in size in relation to the length of the face. These changes make it difficult for the dog to breathe. Imagine trying to drink a thick milkshake through a normal, narrow straw, rather than a wide milkshake straw. It is possible, but requires a lot more effort. If you continued this for the whole drink you would be very tired by the end. This is how it feels for brachycephalic dogs to breathe through narrowed airways. 

The anatomical changes that cause BOAS are present from birth. However, over time secondary changes occur such as swelling and sagging of the tissues around the airways. There can also be changes elsewhere in the body, due to the extra pressure on the heart and lungs. Because the dog is already breathing with increased effort, anything that requires more exertion (such as hot weather or intense exercise) can lead to lack of oxygen and collapse. BOAS can affect a dog’s ability to exercise and play normally.

Common symptoms of BOAS include:

  • Snuffling and snorting
  • Panting excessively
  • Snoring when asleep
  • Exercise intolerance
  • Frequent gulping
  • Vomiting up white froth when excited
  • Sleeping in unusual positions (e.g. sitting up or with the head elevated)
  • Fainting episodes
  • Stopping breathing for short periods while asleep

Which tests are used to diagnose BOAS?

The airways cannot be directly examined without anaesthesia, although presence of the symptoms described above give a strong suspicion of BOAS. Several grading systems exist, such as the Respiratory Function Grading Scheme created by Cambridge University and the Kennel Club. This gives dogs a grade based on their respiratory noise and effort, both at rest and after 3 minutes of exercise, and is suitable for dogs over 12 months of age. Grades 0-3 are possible, with surgical treatment recommended for dogs scoring grade 2 or 3. Cambridge University also offers functional grading for brachycephalic dogs by measuring respiratory pressures, however this is not essential as dogs showing the symptoms listed above are likely to have typical changes. Only specific vets are approved to carry out the BOAS grading listed above, and a list is available on the Kennel Club website – this is primarily designed to look at breeding potential. There are certain surgical procedures that can alleviate some of the symptoms of BOAS - your own veterinary surgeon can assess your dog and determine if surgery is recommended without the need for an official grading.

What does surgery involve?

Dogs are placed under anaesthetic for full assessment. Often, an x-ray is taken of the chest to assess the size of the trachea (windpipe) and look for any evidence of infection in the lungs. Once the dog is fully asleep, the airways are assessed. There are four key areas of anatomy which are commonly affected in dogs with BOAS:

  • Stenotic (narrow) nostrils
  • Overlong, thick soft palate
  • Everted, swollen tonsils
  • Everted laryngeal saccules

Depending on the changes present, surgery is performed to try and correct the anatomical abnormalities. Various techniques are available to shorten the soft palate so that it no longer hangs into the airway. Some of these techniques also thin the palate; a thick, soft palate is more common in French Bulldogs and English Bulldogs. If the tonsils and laryngeal saccules are everted, they may be removed. Almost all dogs with BOAS have narrow nostrils; these are widened to allow increased air flow.

Dogs are monitored very closely during recovery to make sure they wake up slowly and stay calm. Depending on the patient and clinic preference, they may be discharged later that day or hospitalisation may be advised for observation overnight. Management of BOAS cases is complex; surgery is not routinely performed at all veterinary practices, and may require specialist referral.

What are the potential complications?

Surgery to try and correct BOAS is not without risk. However, animals who are severely affected and are not treated are unlikely to reach a normal lifespan. Dogs with BOAS have changes present from a young age, but may show only mild signs in the first few years of life. Symptoms often progress as secondary changes develop. There is no point at which surgery is completely safe. However, risks are lower if we intervene before signs become severe. The main risks of surgery are:

Death

Anaesthetics carry a small risk in every animal; this increases in older, overweight or unwell pets. Surgery in and around the airways carries a risk of swelling post-op, which is potentially dangerous. This risk is reduced if surgery is carried out by an experienced team, and patients are monitored closely in the post-operative period, but death during the procedure or in the 24-hours post surgery is possible. More severely affected patients are at higher risk.

Aspiration Pneumonia

Brachycephalic patients are prone to regurgitation (like acid reflux) due to their shape and anatomy. Although it is generally undesirable that extra tissue covers the airways, it does help reduce the risk of reflux being inhaled. After surgery, the risk of aspiration increases while patients adjust to their new airways. We often give an antacid to reduce the likelihood of regurgitation and inhalation. Feeding from a height following surgery also helps reduce the risk. Some patients may aspirate and develop a mild chest infection which requires antibiotics. Less commonly, this can be serious (known as Aspiration Pneumonia) and could require intensive treatment or hospitalisation.

What is the outlook for dogs with BOAS?

After surgery, dogs will need to be kept quiet to prevent excessive swelling in the airways. Toilet walks only are recommended for the first 7-14 days, and unnecessary excitement like playing with toys or other dogs should be avoided. During this time, it is recommended to feed wet food, rolled into meatballs and hand-fed from a height. This helps ensure food is swallowed directly, reducing the risk of aspiration.

BOAS is a complex condition. Although there are several components we can address surgically, there are also many changes we are unable to do anything about, such as a thick tongue base, narrow trachea (wind-pipe), and presence of excess tissue in the nasal cavity (aberrant turbinates). For the majority of dogs, BOAS surgery leads to a significant improvement in symptoms and quality of life. For a small number of patients, surgery makes only a small difference, as the other components of BOAS play a larger part in their disease. Other management techniques such as weight control may help, but for those most severely affected, specialist referral may be required.

Disclaimer

Please note that the content made available on this webpage is for general information purposes only. Whilst we try to ensure that at the time of writing all material is up to date and reflects industry standards, we make no representation, warranties or guarantees that the information made available is up to date, accurate or complete. Any reliance placed by yourselves is done so at your own risk.

Page last reviewed: 14th May 2025

Next review due: 14th May 2027

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