What is Brachycephalic Obstructive Airway Syndrome (BOAS)?
Brachycephalic animals are those that have short heads and short noses, these include most Bulldogs, Pugs, Cavalier King Charles Spaniels, Boxers and other breeds. BOAS is the term given to a number of syndromes that result from the shortened head and nasal passage of these animals, which causes altered or decreased airway flow through the upper airways. These animals often struggle to breathe during exercise and are very susceptible to overheating due to their inability to pant to control their body temperature.
What is involved in BOAS?
There are five significant abnormalities in the upper airways of brachycephalic animals: stenotic (narrow) nares (nostrils), an elongated soft palate, everted laryngeal saccules, laryngeal collapse, and hypoplasia of the trachea (where the trachea is too small for the size of the animal – this is most commonly seen in the English Bulldog). The problems and subsequent changes are listed in more detail below.
- Stenotic nares: Narrowing of the nostrils increases the resistance to airflow as brachycephalic animals are breathing. Their nasal cartilages also tend to collapse in on each other during inspiration. This results in the animal requiring an increased amount of effort to breathe and get air into the lungs.
- Elongated soft palate: A long soft palate obstructs the flow of air into the trachea, and causes the air movement to become turbulent (instead of linear air flow), which further increases the effort required to breathe. This also results in inflammation of the upper airway. Stenotic nares and elongated soft palate are the two primary problems seen in this condition. The resulting increased effort required for breathing results in the following secondary problems.
- Everted laryngeal saccules: The increased pressures exerted during breathing causes the laryngeal saccules (tonsils) to enlarge and protrude into the back of the mouth. This further narrows the airways, reducing the amount of air that the animal can transfer during breathing.
- Laryngeal collapse: Gradual collapse of the larynx occurs due to the increased pressures exerted during breathing. This collapse is often progressive, but the rate of progression can be slowed with treatment.
- Acid reflux: Similar to heartburn in humans. Acid from the stomach enters the oesophagus due to the altered pressures in the upper airway, resulting in inflammation and possible ulceration of the oesophagus and stomach.
- Tracheal hypoplasia: A small trachea is a primary problem seen predominantly in the English Bulldog. This problem results in a significant reduction in the amount of air that the animal can get into their lungs.
What clinical signs will I see if my animal has BOAS?
The clinical signs of BOAS are often progressive in nature.
A common presenting complaint is that your dog snores very loudly when asleep, and even when awake and resting. When these dogs exercise they often pant excessively and have difficulty exercising when it is hot outside, often taking a long time to recover. Other signs include shortness of breath, snoring, wheezing, gagging, regurgitation. Some dogs collapse during or after exercise or when they get excited, and can become so badly affected that they lose consciousness due to lack of oxygen.
How is BOAS diagnosed?
When performing a physical examination, your surgeon will assess the anatomy of your pets head and discuss any clinical signs you may be seeing at home. Most brachycephalic animals will have a degree of upper airway obstruction, but the aim is for your surgeon to determine whether your pet is experiencing a significant level of clinical signs currently or has an anatomical conformation that will predispose them to problems in the future.
Only the nostrils can be properly assessed during a physical examination. Unfortunately, your animal will require a general anaesthetic to confirm the presence of the other abnormalities associated with this condition. General anaesthesia in brachycephalic dogs is associated with an increased risk, predominantly during the induction and recovery phases. For this reason we recommend confirming the diagnosis and heading straight to surgical correction in order to decrease the risk of complications when your pet is recovering from anaesthetic. We know that surgical correction of these problems can significantly decrease future anaesthetic risks these patients.
What treatment options are available for my dog with BOAS?
Surgery is the best option to improve the airways and is the best way to slow down the progression of the airway disease. Unfortunately, these brachycephalic patients will never be greyhounds and be able to run for long periods of time. The aim of surgery is to improve the airway as much as possible, to improve their quality of life and slow down the progression of any collapse that is occurring.
- Stenotic nares: A section of cartilage is removed from the nostrils which allows increased air flow to pass through the nostrils.
- Elongated soft palate: The section of the soft palate that is too long is removed which results in decreased interference with air flow into the larynx.
- Laryngeal collapse: Depending on the severity of collapse, surgical repair may be as simple as removal of excess tissue that is interfering with airflow, or in severe cases a permanent tracheostomy may be the only viable procedure.
- Everted laryngeal saccules: The saccules present at the back of the mouth can be removed to increase the area available for air flow.
In addition to surgical procedures, weight management is imperative in the management of this condition. Weight loss can drastically improve the airflow through the pharynx and neck.
Although we are trying to improve the airways, surgery does cause trauma and inflammation to the area. The complication rate for BOAS surgery is approximately 10% and they range from mild to severe. Complications can include aspiration pneumonia, upper airway obstruction (due to inflammation) and bleeding. We do our best to reduce the chance of these complications occurring by using medications to keep them calm post-operatively as well as pre-operative medications to prevent regurgitation and resulting aspiration pneumonia.
If the complication is severe enough, some patients require intervention. In most cases this is an extended hospital stay with oxygen support but in some cases more aggressive treatment is required. In rare cases a tracheostomy tube has to be placed in the neck to bypass the upper airway, this is normally temporary but, in some cases, a permanent hole needs to be created. These more severe complications are not common but can occur in patients despite all efforts to avoid them.
During recovery, patients are monitored 24/7 in our ICU. If there are any early signs that they are having trouble breathing or there are any concerns we are able to address them immediately.
Animals suffering from clinical signs of BOAS who receive prompt treatment will have a significant improvement in exercise tolerance and their ability to breathe will improve. As surgery cannot completely create a normal airway in brachycephalic animals, they will always remain susceptible to heat stress and have a degree of exercise intolerance.
Early treatment will slow the progression of laryngeal collapse which maximises the benefit from surgery. Many dogs will not experience further laryngeal collapse if their nares and soft palate are treated promptly, however some dogs will continue to progress and may require surgery.
A hypoplastic trachea cannot be treated, and these dogs are often significantly affected by the impaired airflow associated with this condition.