Brachycephalic Syndrome

Aberrant turbinates and nasal septal deviation.  Inside the nose there are a series of cartilages that form channels to allow airflow and heat exchange.  In brachycephalic dogs there is sometimes excessive cartilage (aberrant turbinates) that can obstruct the nasal passages, impairing airflow and heat exchange.  In some dogs the intranasal septum can deviate to one side resulting in narrowing of one side of the nasal cavity.

Elongated soft palate.  The soft palate is the fleshy tissue at the roof of the mouth which serves as an anatomical separation between the nasopharynx and oropharynx (the spaces at the back of the nose and mouth respectively).  In brachycephalic dogs the soft palate is invariably too long and sometimes too thick, and this results in airway obstruction and swallowing dysfunction.  Dogs with an elongated soft palate exhibit noisy breathing (stertor), reverse sneezing, difficulty swallowing, and retching.

Tracheal hypoplasia.  The trachea or windpipe in brachycephalic dogs can be considerably narrower than non-brachycephalic breeds of a similar size.  The narrow diameter of the trachea impedes airflow to the lungs.  In addition, dogs with tracheal hypoplasia may have impaired ability to clear mucus and debris from their airways and are predisposed to secondary respiratory infections.

Dogs with BOAS work harder than unaffected dogs to breathe (a bit like when we try to breathe through a blocked nose).  This generates high pressure gradients within the airways and body cavities, which over time can lead to secondary laryngeal problems.

Everted laryngeal saccules.  Turbulent airflow and high negative pressures within the airways leads to swelling and bulging of the mucosal tissue between the vocal cords.  This tissue can bulge into the lower half of the larynx causing permanent obstruction.  The images below show a normal larynx compared with that of a brachycephalic dog with everted laryngeal saccules.

Laryngeal collapse.  In more advanced cases we can see inward collapse of the laryngeal cartilages resulting in severe obstruction of the entrance to the windpipe.  This is usually a dynamic problem worsened by heat or exertional stress.  It also tends to worsen with chronicity, which is why it is better to operate on these dogs early in the disease process before there are secondary laryngeal changes.

How do you know if your dog is affected?

Patients with BOAS can exhibit a number of signs relating to their respiratory system and digestive system.

• Exercise and stress intolerance.  Dogs with BOAS have physiologically adapted to cope with their upper respiratory obstruction.  However, these compensatory mechanisms usually fail when these patients become excited or stressed, and oxygen delivery to critical tissues such as the brain is compromised.  This results in these dogs tiring easily and getting out of breath.  In severe cases we can see collapsing or fainting episodes.
• Heat intolerance.  Dogs rely heavily on heat exchange in the nasal cavity and during panting in order to cool down.  These processes are ineffective in dogs with upper airway obstruction, and patients with BOAS can overheat very quickly.  Dogs with heat stroke will be seen to pant excessively, which worsens their respiratory obstruction and causes them to overheat further, leading to heat stroke.  If not promptly treated, heat stroke is a life-threatening condition.
• Sleeping disorders.  Most dogs with BOAS will snore heavily while asleep owing to vibration of the redundant soft palate at the back of the throat.  More worryingly, when the mouth is closed there is partial or sometimes complete obstruction of the nose and throat, making it difficult or impossible for these dogs to breathe.  Affected patients find it difficult to get into a comfortable position to sleep, and when they do sleep their breathing pattern and sleeping pattern can be interrupted.  In severely affected dogs we can see obstructive sleep apnoea, whereby breathing is arrested and the dog can wake up gasping for breath.
• Reverse sneezing.  Backwards sneezing or paroxysmal respiration is seen commonly in brachycephalic dogs.  It is characterised by bouts of rapid inhalation of air through the nose.  Typically the dog will stand with its head and neck extended and make snorting or honking sounds.  Such episodes last from a few seconds to a minute.  The cause of reverse sneezing is unknown but it is thought to be due to irritation of the back of the throat owing to the elongated soft palate in these breeds and silent gastro-oesophageal reflux.  These episodes are not harmful but they can be distressing for both you and your dog.
• Difficulty eating.  Many dogs with BOAS will have difficulty swallowing their food and can choke or gag during swallowing.  This is due to their elongated soft palates and redundant pharyngeal function.  Some of these patients may also have impaired function of their pharyngeal muscles.
• Noisy breathing.  Most dogs with BOAS have very noisy breathing called stertor.  This is a loud snoring sound which often worsens when these patients are stressed or exerted and begin to pant.  Some dogs will have a wheezing or gasping sound called stridor, which is an indicator of more severe respiratory obstruction.
• Gastro-oesophageal reflux, regurgitation and vomiting.  Many brachycephalic dogs will be seen to ‘vomit’ white froth, typically when they are excited or stressed, a phenomenon known as gastro-oesophageal reflux.  Some patients will also frequently ‘vomit’ undigested food shortly after swallowing or several hours later.  Many of these dogs show signs of nausea such as frequent licking of their lips and excessive salivation.  The white froth seen in these patients is acidic and can, over time, cause irritation and damage to the throat.  There is a risk that this froth or food can be inhaled during these episodes, leading to inhalation pneumonia or, in severe cases, acute airway obstruction.

What can be done to help these patients?

Dogs affected by BOAS almost always benefit from surgical correction of their upper airway abnormalities.  At Swift, we have extensive surgical experience of treating these patients, and this is complemented by an equally experienced surgical nursing and ICU team.

When your dog is referred you will have a 20-40 minute consultation with the surgeon, who will examine your pet, identify the problems relating to the airway disease, and discuss the further diagnosis and surgical treatment of these patients.