Brachycephalic Obstructive Airway Syndrome (BOAS)

Brachycephalic obstructive airway syndrome refers to a group of upper airway abnormalities that result from the shortened skull of flat-faced breeds. The soft tissues of the nose, throat, and airway don't shrink in proportion to the shortened bones, leading to multiple obstructions:

• Stenotic nares: Narrowed nostrils that restrict airflow
• Elongated soft palate: Excess tissue at the back of the mouth that partially blocks the airway
• Hypoplastic trachea: A narrower-than-normal trachea (particularly in Bulldogs and Pugs)
• Everted laryngeal saccules: Small pouches in the larynx that turn outward when the dog chronically strains to breathe, further obstructing airflow
• Nasopharyngeal turbinates: Intranasal structures that extend into the airways where they cause obstruction

Individually, each abnormality may cause mild impairment. In combination - as is typical - they cause significant respiratory compromise that worsens with exercise, heat, and excitement.

Grading BOAS

BOAS is graded 0–3:

• Grade 0: No respiratory signs
• Grade 1: Occasional noise; no exercise intolerance
• Grade 2: Regular snoring; mild exercise intolerance; some respiratory effort
• Grade 3: Severe noise; significant exercise intolerance; episodes of respiratory distress; cyanosis possible; sleep disruption

Most flat-faced breed owners underestimate their dog's severity because they've normalised what they hear. A Grade 2 dog that snores loudly and slows quickly on walks is not simply "a snuffy breed" - it has significant airway compromise.

What to monitor

Log weekly:

• Noise at rest: None, occasional, constant. Note character (snoring, snuffling, wheezing).
• Sleep quality: Does the dog sleep through the night, or wake themselves up? Do they sleep in unusual positions (propped up, chin on elevation) to open the airway?
• Exercise tolerance: How far can the dog walk before showing respiratory distress (heavy open-mouth breathing, reluctance to continue, slowing)?
• Recovery time: After exercise or excitement, how long before breathing returns to normal?
• Heat response: Does hot weather significantly worsen breathing?
• Eating behaviour: Brachycephalic dogs often gulp air when eating, causing regurgitation. Note frequency of vomiting or regurgitation.
• Distress episodes: Note any episodes of cyanosis (blue-grey gums or tongue), severe respiratory distress, or near-collapse.

BOAS testing

The whole body barometric plethysmography (WBBP) test is an objective assessment of airway resistance, available at some veterinary referral centres (Cambridge Veterinary School developed and uses this test). It categorises dogs into BOAS grades with objectivity beyond clinical observation. Useful for surgical planning and breeding assessment.

Surgery

Surgery to correct BOAS abnormalities is highly effective for Grade 2–3 dogs and significantly improves quality of life:

• Widening stenotic nares: A minor procedure, often done under a brief anaesthetic, that opens the nostrils and provides immediate improvement
• Shortening the elongated soft palate: Removes excess tissue to open the airway at the back of the throat
• Laser surgery on nasopharyngeal turbinates: Reduces intranasal tissue

Early surgery (12–18 months) is recommended before secondary changes (everted laryngeal saccules, pharyngeal collapse) develop. These secondary changes are caused by years of straining against the obstruction.

Heat and BOAS - a serious risk

Brachycephalic dogs are severely limited in their ability to cool through panting - the mechanism that regulates body temperature in dogs. In hot weather, BOAS dogs are at high risk of heatstroke:

• Avoid exercise in temperatures above 18–20°C
• Never leave in a hot car
• Avoid midday walks in summer - early morning or evening only
• Always carry water
• Know the signs of heatstroke: excessive panting, drooling, brick-red gums, confusion, collapse

Log weather conditions alongside respiratory signs to identify heat sensitivity threshold.

When to contact your vet

Go to the emergency vet immediately if:

• Gums or tongue are blue or grey (cyanosis)
• The dog cannot settle and is clearly in respiratory distress
• Suspected heatstroke

Contact your vet soon if:

• Grade 2+ signs are present and surgery hasn't been discussed
• Signs are worsening
• Regurgitation is frequent and affecting weight or appetite

Frequently Asked Questions

Is snoring in flat-faced breeds normal? Some noise is expected, but significant snoring and respiratory noise represents compromised breathing - it's the sound of air being forced through a narrow airway. "Normal for the breed" does not mean "healthy for the dog." Severity assessment and surgical discussion is appropriate for regularly snoring brachycephalic dogs.

At what age should surgery be considered? Ideally, 12–18 months of age before secondary changes develop. Earlier surgery (from 6 months in some cases) is performed for severely affected puppies. Surgery can be performed at any age but is less effective when secondary changes are established.

Will my dog definitely need surgery? Not necessarily. Grade 0–1 dogs can be monitored. Strict weight management, avoiding heat and over-exercise, and monitoring for worsening are appropriate for mild cases. Grade 2–3 dogs almost always benefit from surgical correction.

My Frenchie is breathing fine. Why does my vet keep mentioning BOAS? Many brachycephalic owners have normalised their dog's breathing as "just how they sound." Objective testing frequently reveals significant airway compromise in dogs whose owners describe them as breathing normally. If your vet is recommending a BOAS assessment, it's because they have observed something in the examination that warrants investigation.

Does BOAS affect lifespan? Severe, unmanaged BOAS reduces quality of life and increases the risk of fatal respiratory episodes, particularly in hot weather. Well-managed or surgically corrected dogs can have a normal lifespan. The long-term welfare implications of severe BOAS are part of the ongoing debate about the ethics of breeding extreme brachycephalic conformations.