What is Brachycephalic Obstructive Airway Syndrome (BOAS)?

The terms “Brachycephalic Obstructive Airway Syndrome” (BOAS) and “Brachycephalic Airway Obstruction Syndrome” (BAOS) refer to a set of respiratory problems resulting from the abnormal anatomy of “smooshed face” (brachycephalic) dog and cat breeds. Commonly affected brachycephalic dog breeds include English Bulldogs, French bulldogs, Pugs, Boston Terriers, Shih-Tzus and Pekingese. Cat breeds that may be affected include Persians and Himalayans.  

Why are only certain dog breeds affected by Brachycephalic Syndrome?

Breeds with short noses have been selectively bred to have extreme features. Their disproportionate conformation is often accompanied by a number of malformations, including significant distortion of their respiratory anatomy. 

What are the anatomic abnormalities that comprise this syndrome?

  • Stenotic Nares (Nostrils): Affected dogs and cats often have abnormally narrow or flattened nostrils that do not allow a normal amount of airflow. Combined with their abnormal turbinate structure, this causes the effected individual to need to generate a greater-than-normal amount of negative pressure to draw air into their airway. In addition to physical fatigue from an increased effort to breathe, this can cause swelling and inflammation in the dog’s nasal passages and throat that further exacerbate breathing difficulties. 
  • Nasopharyngeal Turbinates: Because affected pets have a similar total amount of nasal turbinate tissue to longer-nosed breeds, but much less space to fit it into, their turbinates are often densely packed and tortuous, and may protrude out of the back of the nasal cavity into the upper part of the pharynx (the nasopharynx).
  • Elongated Soft Palate: The soft palate in a dog is a layer of tissue extending back from the hard palate partway into the throat that serves to separate the upper airway from the back of the mouth. In brachycephalic breeds, the soft palate is often too long for their shortened face and throat, and extends too far back. In this position, the end of the soft palate frequently either partially or fully blocks the larynx, preventing air from passing into the windpipe. The body’s natural response to this is to further increase the amount of negative pressure generated by the lungs to draw air in. This increase in negative pressure causes swelling of the soft palate and other pharyngeal tissues, which further compromises respiratory function.
  • Everted Laryngeal Saccules: The laryngeal saccules are two deep pockets that exist to either side of the vocal cords. When excessive negative pressure is generated by a dog or cat with BOAS, these pockets are pulled into the pharynx similar to the way we might pull the lining of a pants pocket out while emptying its contents. This everted tissue further decreases airflow and exacerbates the patient’s condition. 
  • Laryngeal Collapse: Over time, the excessive negative pressure generated in the pharynx and larynx results in weakening of the cartilages that maintain the structure of the larynx. This weakened cartilage can become progressively deformed, further impeding the movement of air. There is evidence that bronchial collapse is often also present in individuals exhibiting signs of laryngeal collapse.
  • Hypoplastic Trachea: Affected pets often have a trachea (windpipe) that is disproportionately narrow for their body size. This limits the rate that air can flow into and out of the lungs, and further increases airway resistance. While it is pathophysiologically not considered a component of BOAS, this condition is very frequently present in individuals suffering from BOAS.  

What other Problems are associated with Brachycephalic Airway Syndrome?

  • Diseases of the esophagus and stomach: A disproportionate number of pets with BOAS appear to be affected by gastroesophageal reflux and both functional and structural diseases of the stomach. It appears that these may be a result of the progression of their airway disease, but further research is necessary to confirm this. It is important to detect and treat any upper GI diseases that may be present in these patients, even if they are not causing obvious clinical signs.
  • Heat Stroke: Because a dog’s primary means of dissipating heat is through expelling heated air (panting), dogs with BOAS have a significantly compromised ability to thermoregulate. They are at much higher risk of getting heat stroke than dogs with a normal airway, and can develop heat stroke even under relatively mild conditions.  

How can I tell if my dog has Brachycephalic Syndrome?

All brachycephalic prone dogs suffer from BOAS to some degree, but some are more severely affected than others. The most minimally affected dogs can often live their entire lives without showing much distress, although they nonetheless must constantly exert increased effort to breathe. More severely affected dogs will display various degrees of respiratory distress and digestive troubles, ranging from being occasionally short of breath to collapsing with even minimal exercise.

The most common signs of BOAS in dogs include stertorous (noisy) breathing (usually described as snorting), gagging, regurgitation, persistently elevated breathing rate, elevated respiratory effort (heaving sides, stretching of the head and neck upward, holding elbows out to the sides), decreased exercise tolerance, collapse, and blue or gray discoloration of the gums (cyanosis). Most dogs with BOAS snore loudly due to airway obstruction while sleeping (similar to obstructive sleep apnea in humans), and may awaken frequently.  

It is important to recognize that what is frequently perceived as being “normal for the breed” because it is so widespread is actually physiologically abnormal and dangerous to the animal. 

If your dog is brachycephalic or suffers from BOAS, talk to your veterinarian to determine if your dog would benefit from BOAS surgery or treatment.

How is Brachycephalic Syndrome diagnosed?

The diagnosis of Brachycephalic Syndrome is primarily clinical, based on a physical exam and history of consistent clinical signs. To fully assess the multiple components of this syndrome, an examination of the pharynx and larynx under general anesthesia and chest x-rays are performed. Endoscopic examination of the nasal passages (rhinoscopy) and trachea/bronchial tree (bronchoscopy) and a CT or MRI scan of the head and neck may also be performed in some cases. 

Due to the association between BOAS and upper GI problems, an endoscopic examination of the esophagus, stomach, and upper intestine is often useful in diagnosing and treating concurrent GI diseases.  

How is Brachycephalic Syndrome treated?

The goal of treatment for Brachycephalic Syndrome is to open up the airway as much as possible to allow for improved airflow. It is important to understand that the airway cannot be made completely normal, and it is rare for all symptoms to resolve. Treatment is considered successful when a significant improvement in symptoms is achieved.

Surgical management of Brachycephalic Syndrome involves widening of the nares (nostrils), resection of the excess soft palate, and removal of everted laryngeal saccules. Laser-assisted turbinectomy is being evaluated as a treatment option for nasopharyngeal turbinates, but is not widely available. In most instances, these surgical interventions result in sufficient long-term improvement that no further airway surgery is necessary. In a subset of the most severely affected patients, further treatment proves necessary due to progressive deterioration.

No treatment exists for a hypoplastic trachea, but often when the other airway abnormalities are addressed, improvement is significant enough that lifestyle changes such as exercise restriction and cooling precautions can minimize the impact of this abnormality.  

Because brachycephalic animals present an increased risk for anesthesia and surgery due to their abnormal airway, they must be particularly closely monitored through the perioperative and postoperative periods. They are at an increased risk for postoperative complications such as aspiration pneumonia, which can become life-threatening. For this reason, most patients are hospitalized for at least 48 hours following their airway surgery.

Often, medications are prescribed for up to a month after surgery to control airway inflammation and any GI abnormalities that have been identified. In most instances, digestive signs resolve following their corrective surgery and do not recur, although careful monitoring remains important.

What is the prognosis for Brachycephalic Syndrome?

The long- term prognosis for Brachycephalic Syndrome varies widely depending on the severity of their airway abnormalities. Dogs with mild to moderate Brachycephalic Syndrome tend to do very well after surgery, and typically go on to live relatively normal lives. Dogs with severe Brachycephalic Syndrome have a more guarded long-term prognosis. These patients may need multiple surgeries over the course of their lives, and typically also require strict lifestyle management to minimize the impact of their disease. Lifestyle management consists of strictly limiting physical activity, avoiding situations that may cause excitement or anxiety, and maintaining a cool environment. 

About 95%-98% of dogs experience improvement in their airway symptoms with surgery. Virtually all brachycephalic dogs benefit from having their upper airways addressed. Even dogs who don’t seem obviously affected will require less effort to breathe, and will be more physically active and heat tolerant than before surgery. Additionally, owners often notice that their dog is able to sleep better and experiences less digestive problems than they did prior to surgery.


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