What is BOAS?
Brachycephalic’ is derived from the Greek language, whereby ‘brachy’ means short, and ‘cephalic’ means head, i.e. breeds of dogs and cats with short heads.
This anatomic difference means there is less room for airflow in the upper respiratory tract than other breeds, resulting in increased airflow resistance, and obstruction. Symptoms can range from relatively mild snoring, to severe difficulty breathing with collapse.
Symptoms are not just confined to breathing problems though. Dogs with clinically significant BOAS can also suffer from gastrointestinal issues, such as regurgitation and vomiting, poor sleep (sleep apnoea), and a much higher chance of overheating (heat stroke).
Are all breeds affected?
Any brachycephalic breed can be affected by BOAS. The most common breeds affected include
- - French bulldog
- - English bulldog
- - Pug
- - Shih Tzu
- - Boxer
- - Pekinese
- - Cavalier King Charles Spaniel
The most common cat breed affected is Persian.
Why do these problems develop?
The overriding reason for this condition is due to excessive soft tissues in the head relative to the size of the skull. Affected areas include the external nostrils, internal nasal cavity, soft palate, larynx, tonsils, tongue and trachea (windpipe).
In many dogs affected by BOAS, the external nostrils will be narrowed and the outside part of the nostrils collapse during inspiration. This results in a much larger resistance to airflow, requiring more effort to breathe through the nose.
The nasal cavity itself can be overcrowded with the normal bones (turbinates), and the soft tissue covering the bones can be thickened, which reduces the amount of free space for air to flow. One of the functions of these tissues in the nasal cavity is to cool the body temperature. If there is significant enough obstruction to airflow, then the body’s ability to cool down is severely compromised, and the risk of heat stroke is high.
The soft palate will often be over-long, causing obstruction and turbulence of airflow around the larynx. This can result in secondary changes of the larynx (laryngeal collapse), swelling and eversion of the tonsils, and thickening of the tissues in the throat.
Increased negative pressure, or vacuum-effect in the throat can also result in secondary gastric disturbances such as acid reflux, and heart failure.
Although not directly a problem of the skull, some dogs (particularly English bulldogs), are born with a very narrow trachea, which further increases the effort required to breathe.
Diagnosis and investigation
The most common age of developing symptoms is between 1-4 years, but some will be diagnosed later or earlier.
Diagnosis is generally made on physical examination, and following a thorough assessment of your pet’s history. Often, an exercise tolerance test will be performed if there is any doubt whether BOAS is present or not.
Only the external nostrils are able to be examined consciously but a good estimation of likely problem areas will be made after examination.
Investigation of the upper airway will require a light anaesthesia to allow full assessment of the anatomy.
Certain diagnostic tests may be needed, based on the findings of physical examination, and include:
- chest X-rays
- blood test
- endoscopy of the nasal cavity and/or oesophagus
- CT scan of the skull
Treatment options
The aim of treatment is to improve the airflow through the upper airway, improving the quality of life for your pet. It is not possible to give them a completely ‘normal’ airway.
If BOAS is diagnosed, it is likely that surgery will be recommended, although some cases may be more appropriately treated medically.
Each patient is treated individually, based on their symptoms, examination and diagnostic test results. As brachycephalic breeds are an inherently higher risk of anaesthesia, it would be generally recommended to perform surgery immediately following any diagnostics performed.
Surgery is a multi-level procedure, aimed at alleviating obstruction wherever it is present. This may include:
- widening the nostrils
- removal of internal nasal cartilage
- shortening and/or thinning the soft palate
- removing tonsils (tonsillectomy)
- removing swollen laryngeal saccules (stage 1 laryngeal collapse)
- removing nasal turbinate bones or volumetric reduction (this is rarely performed on first surgery)
Are there risks?
Severely affected BOAS patients are higher risk before, during and after anaesthesia. Problems that can develop include swelling around the larynx, bleeding, regurgitation and aspiration of stomach contents into the lungs. These can be potentially life-threatening complications, but if corrective surgery is performed BEFORE symptoms become severe, then the risk is significantly reduced.
What is the prognosis after surgery?
The vast majority of dogs show substantial improvement following surgery. In the first 1-2 weeks you may notice a slight worsening due to post-operative swelling, and mild nose bleeds (if the nose has had surgery). Full assessment of how well surgery has worked is performed at 6-8 weeks. If symptoms have not improved enough, then re-evaluation is required, and may require further treatment of the internal nasal cavity.
It is still very important to appreciate that these dogs are still at risk of overheating, and appropriate precautions should be taken.
Some dogs may start to re-develop symptoms in the future (usually several years), but this is generally limited to those that have very poor anatomic variation.
