What Is BOAS
Brachycephalic Obstructive Airway Syndrome (BOAS) is the constellation of upper airway abnormalities and resulting clinical signs in short-skulled (brachycephalic) dogs — primarily English Bulldogs, French Bulldogs, Pugs, Boston Terriers, Pekingese, Shih Tzu, and some Boxers/Bullmastiffs.
Affects 60-90% of severely brachycephalic dogs to some degree, with substantial impact on quality of life and significant heat-related mortality risk.
The Anatomy Of BOAS
Primary anatomic abnormalities (genetic, present from birth):
- Stenotic nares — narrowed nostril apertures restricting airflow
- Elongated soft palate — too long, obstructs caudal nasopharynx and rima glottidis (vocal cord opening)
- Hypoplastic trachea — smaller-than-expected windpipe
- Nasopharyngeal turbinates — aberrant turbinate growth into the nasopharynx
- Macroglossia — over-large tongue
Secondary changes from chronic negative airway pressure (develop over time):
- Everted laryngeal saccules — vocal cord saccules turn inside out, narrowing airway further
- Laryngeal collapse (stages I-III) — progressive cartilage degeneration
- Tonsillar hyperplasia / eversion
- Gastric reflux / oesophagitis / hiatal hernia — from chronic negative pressure pulling stomach forward
The Cambridge BOAS Functional Grading
The Cambridge BOAS Research Group (Liu, Ladlow, Sargan, et al.) developed the validated functional grading scheme used internationally:
| Grade | Description |
|---|---|
| 0 | Functionally normal — free of respiratory signs |
| I | Mild signs not impacting quality of life — mild stertor at rest, mild post-exercise noise |
| II | Clinically relevant signs impacting exercise tolerance, sleep, or heat tolerance |
| III | Severe respiratory signs at rest — dyspnoea, cyanosis, syncope episodes |
Grade II or higher warrants surgical referral.
The Key Clinical Signs
Respiratory Noise
Stertor vs Stridor:
| Sign | Pitch | Source | Significance |
|---|---|---|---|
| Stertor | Low (snore-like) | Pharyngeal (soft palate) | Common, surgically correctable |
| Stridor | High (harsh) | Laryngeal | More serious — laryngeal collapse |
Stridor at rest is a particularly concerning sign indicating advanced laryngeal collapse.
Exercise Intolerance
Key functional indicator. Brachycephalic dogs may have intrinsically lower exercise capacity but clear regression from normal puppy exercise tolerance suggests progressive BOAS.
Heat Intolerance
Brachycephalic dogs cannot cool effectively through panting due to upper airway obstruction. Heat-related emergencies develop rapidly even at modest temperatures (20-25°C / 68-77°F).
Sleep Disturbance
- Loud snoring (almost universal)
- Witnessed sleep apnoea
- Waking gasping
- Sleeping sitting up or with chin elevated to maintain airway
Gastrointestinal Signs
- Regurgitation (passive, post-meal)
- Gagging
- Vomiting
- Hiatal hernia
These resolve in many dogs after corrective surgery — secondary to chronic negative airway pressure pulling stomach forward.
Emergency Presentations
- Syncope (collapse / fainting) during exertion or heat
- Cyanosis (blue gums) episodes
- Acute respiratory distress requiring oxygen/intubation
Breed-Specific Risk
| Breed | BOAS prevalence (functional Grade II+) |
|---|---|
| English Bulldog | 60-80% |
| French Bulldog | 50-65% |
| Pug | 50-70% |
| Boston Terrier | 30-40% |
| Cavalier King Charles Spaniel | 15-20% |
| Boxer | 10-15% |
| Bullmastiff | 5-15% |
Severely brachycephalic breeds have additional features:
- Pug — hypoplastic trachea common; pug-specific encephalitis
- English Bulldog — heat-related mortality well-documented; multilevel disease often severe
- French Bulldog — additionally predisposed to IVDD, hemivertebrae, allergies
Assessment – The Cambridge BOAS Test
The validated 3-minute fitness test:
- Pre-exercise auscultation — listen for inspiratory noise at neck
- 3-minute paced walk (1 m/s)
- Post-exercise auscultation at 0, 30, 60 seconds post
Scoring:
- Grade 0 — no audible inspiratory noise
- Grade I — mild noise, settles quickly
- Grade II — clearly audible noise, slower recovery
- Grade III — severe noise at rest, severe distress
Endoscopic assessment under sedation for surgical planning:
- Nostril aperture measurement
- Soft palate length / thickness
- Larynx stage of collapse (I-III)
- Saccule eversion assessment
- Trachea diameter / dynamic collapse
Surgical Correction
Multilevel Corrective Surgery
Standard for Grade II+ disease:
- Stenotic nares correction
- Alar wedge resection — most common
- Rhinoplasty (Trader, ala vestibuloplasty) — more aggressive widening
- Staphylectomy (soft palate shortening)
- Conventional partial palatectomy — widely available
- LATE (Laser-Assisted Turbinectomy and palate shortening) — more advanced, specialist
- Folded flap palatoplasty — newer technique
- Laryngeal sacculectomy
- If everted saccules identified during airway exam
Advanced / Salvage Procedures
- Turbinectomy for nasopharyngeal turbinates (specialist)
- Laryngeal tie-back for stage III laryngeal collapse
- Permanent tracheostomy as final salvage option
Outcomes
~80-90% of dogs substantially improved with multilevel surgery in expert hands.
Surgery EARLIER in disease course has better outcomes — less laryngeal collapse means less complex/risky surgery.
Conservative Management (All Grades)
Weight Management
ONE OF THE MOST EFFECTIVE INTERVENTIONS for BOAS — even 10-15% weight reduction can dramatically improve airway function.
- Excess cervical fat narrows airway
- Abdominal fat pushes diaphragm forward
- Realistic 1-2% body weight per week loss
- Prescription weight-loss diets restrict to RER of TARGET weight
- See PuppaDogs Ideal Weight Calculator
Lifestyle Adjustments
- Harness not collar — collars compress trachea
- Raised bed — reduces gastric reflux
- Avoid heat / humidity — no walks above 20-25°C/68-77°F
- Cool surfaces in summer
- AC environment
- Short frequent walks rather than long
- Cooling vest in summer
- Never force exercise
Medical Management
- Prokinetics (metoclopramide, cisapride) for regurgitation
- Acid suppression (omeprazole, famotidine)
- Maropitant for nausea
- NSAIDs / pain relief post-surgery
- Steroids acute for airway swelling
Anaesthesia Risk
BOAS dogs have significantly higher anaesthesia complication risk:
- Desaturation during induction — short reserve, difficult mask
- Regurgitation / aspiration
- Prolonged recovery with airway swelling
- Post-op heat stroke from stress
Best practice:
- Pre-anaesthetic prokinetic + acid suppression + antiemetic
- Specialist anaesthesia ideal
- Slow careful recovery with extended airway monitoring
- 24-hour hospital observation post-corrective surgery
Heat-Related Emergency
Brachycephalic dogs are the highest-risk breeds for fatal heat stroke:
- Cannot cool by panting due to upper airway obstruction
- Heat stroke develops at modest temperatures (20-25°C/68-77°F)
- Onset can be sudden and fatal — minutes to hours
Heat stroke signs:
- Heavy panting → red gums → collapse → seizures → death
- Often within <1 hour if untreated
NEVER LEAVE in cars, avoid midday walks, AC environment essential in summer, cooling mat at home.
Emergency: cool water (not ice-cold), wet towels, fan, AC, transport immediately to vet. See PuppaDogs Heatstroke First-Aid Calculator.
When To Refer
Surgical referral appropriate for:
- Grade II or III BOAS — surgical correction
- Any emergency presentation — syncope, cyanosis, collapse
- Young Bulldogs/Pugs/Frenchies with significant signs — prophylactic correction
- Failed conservative management
Specialist soft tissue surgeons experienced in multilevel BOAS surgery have substantially better outcomes than generalists.
Breeding Considerations
Selecting toward more moderate conformation improves BOAS prevalence:
- Longer muzzle
- Larger nostrils
- Less neck folding
- Less extreme conformation
The UK Brachycephalic Working Group, RSPCA, Crufts conformation changes, and Cambridge BOAS Scheme are all driving improvement.
Dogs with functional Grade II+ BOAS should NOT be bred. Dogs that required corrective surgery are generally not bred.
Honest Caveats
- BOAS is largely genetic conformational — corrective surgery improves but doesn’t cure
- Surgery has inherent risks — anaesthesia, post-op airway swelling, complications
- Some dogs progress despite surgery — laryngeal collapse can be relentless
- Owner commitment to weight management, heat avoidance, and lifestyle is lifelong
- Insurance considerations — many policies exclude breed-specific conditions in brachys; check before purchase
- Cost of multilevel surgery — typically $3000-8000+ depending on region and complexity
Conclusion
BOAS affects 60-90% of severely brachycephalic dogs to some degree and substantially impacts quality of life. The Cambridge functional grading scheme (0-III) is the validated framework — Grade II or higher warrants surgical referral. Multilevel corrective surgery (stenotic nares + staphylectomy + saccule resection) achieves substantial improvement in 80-90% of dogs in expert hands, with better outcomes when performed earlier in disease course. Weight management is one of the most effective interventions — even 10-15% weight loss substantially improves signs. Heat avoidance is critical — brachys cannot cool through panting and have fatal heat stroke risk at modest temperatures. Anaesthesia risk is elevated — specialist care appropriate. Breeding selection toward more moderate conformation is improving population-level outcomes.
Frequently Asked Questions
What is BOAS in dogs?
BOAS (Brachycephalic Obstructive Airway Syndrome) is the constellation of upper airway abnormalities and resulting respiratory signs in short-skulled (brachycephalic) dogs – English Bulldog, French Bulldog, Pug, Boston Terrier, Pekingese, Shih Tzu primarily. Primary anatomic abnormalities present from birth: stenotic nares (narrow nostrils), elongated soft palate, hypoplastic trachea, sometimes nasopharyngeal turbinates. Secondary changes develop over time from chronic negative airway pressure: everted laryngeal saccules, laryngeal collapse stages I-III, gastric reflux. Affects 60-90% of severely brachycephalic dogs to some degree.
What is the difference between stertor and stridor?
STERTOR = LOW-PITCHED SNORING noise from PHARYNGEAL airway (soft palate area) – common in brachys, generally surgically correctable. STRIDOR = HIGH-PITCHED HARSH noise from LARYNGEAL airway – more serious, often indicates LARYNGEAL COLLAPSE. Both are abnormal breathing sounds in dogs. Stridor at rest is particularly concerning – suggests advanced disease that may require more complex surgical correction (laryngeal tie-back for stage III collapse) or even permanent tracheostomy as salvage.
Should my English Bulldog have BOAS surgery?
Depends on functional grading: GRADE 0 (no signs) – no surgery needed, continue lifestyle management. GRADE I (mild signs) – conservative management often adequate; prophylactic surgery considered in young dogs of severe brachy breeds. GRADE II (clinically relevant signs impacting QOL) – SURGERY RECOMMENDED. GRADE III (severe signs/emergencies) – URGENT SURGERY. The Cambridge BOAS Research Group validated 3-minute fitness test grading is the gold standard. Earlier surgery has BETTER outcomes – less laryngeal collapse develops. Standard multilevel surgery: stenotic nares correction + staphylectomy (soft palate) + laryngeal sacculectomy if needed. About 80-90% of dogs substantially improved in expert hands.
Why do brachycephalic dogs overheat so easily?
Dogs cool primarily through PANTING – air moves over moist surfaces of tongue and upper airway, evaporative cooling reduces blood temperature. Brachycephalic dogs have UPPER AIRWAY OBSTRUCTION (stenotic nares + elongated soft palate + sometimes hypoplastic trachea) which DRAMATICALLY REDUCES PANTING EFFICIENCY. They cannot dissipate heat effectively even at MODEST temperatures (20-25C/68-77F). Heat stroke develops RAPIDLY – heavy panting -> red gums -> collapse -> seizures -> death within an hour if not addressed. NEVER leave brachys in cars; avoid midday walks; AC environment in summer; cooling mat at home. Brachycephalic dogs have the HIGHEST breed-specific heat stroke mortality.
Can BOAS be cured?
BOAS is largely GENETIC CONFORMATIONAL – the dog will always be brachycephalic. Surgery IMPROVES but doesn’t CURE. Goals of treatment: reduce airway resistance, improve quality of life, reduce risk of heat stroke and acute respiratory crisis. Standard multilevel corrective surgery (nares + soft palate + saccules) achieves SUBSTANTIAL IMPROVEMENT in 80-90% of dogs in expert hands. However: laryngeal collapse can PROGRESS despite surgery; some dogs need REPEAT surgery; OWNER COMMITMENT to lifestyle (weight, heat avoidance, harness, raised bed) is LIFELONG. Best outcomes when surgery performed EARLY before extensive laryngeal collapse develops.
How much does BOAS surgery cost?
BOAS multilevel corrective surgery typically costs USD 3000-8000 in the US, GBP 2000-5000 in the UK, EUR 2500-6000 in EU, depending on: REGION and clinic; specialist vs general practitioner surgeon; SCOPE of surgery (nares only vs full multilevel); concurrent assessment (airway endoscopy under sedation typically included); HOSPITALISATION (post-op monitoring often 24 hours for moderate-severe cases). Many pet insurance policies EXCLUDE breed-specific conditions in brachys including BOAS – check policy carefully before buying brachy puppy. Specialist surgical referral has BETTER OUTCOMES (80-90% improvement) and is worth the additional cost for moderate-severe cases.
Related PuppaDogs Calculators
Continue building your dog’s personalised care plan with these related PuppaDogs calculators:
- Dog Pregnancy / Whelping Due-Date Calculator
- Puppy Weight Predictor (Adult Weight Calculator)
- Heatstroke Risk Calculator for Dogs
- Bloat (GDV) Risk Calculator for Dogs
- Dog Life Expectancy Calculator (Breed, Body Condition, Lifestyle)
- Spay/Neuter Timing Calculator for Dogs (Breed-Specific)
References & Further Reading
The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.
- Liu NC, Sargan DR, Adams VJ, Ladlow JF. Characterisation of brachycephalic obstructive airway syndrome in French Bulldogs using whole-body barometric plethysmography. PLOS ONE, 2015.
- Liu NC, Adams VJ, Kalmar L, Ladlow JF, Sargan DR. Whole-body barometric plethysmography characterizes upper airway obstruction in 3 brachycephalic breeds. JVIM, 2016.
- Riggs J, Liu NC, Sutton DR, Sargan D, Ladlow JF. Validation of exercise testing and laryngeal auscultation for grading brachycephalic obstructive airway syndrome in pugs, French bulldogs, and English bulldogs by using whole-body barometric plethysmography. Veterinary Surgery.
- Trostel CT, Frankel DJ. Brachycephalic airway syndrome. Compendium on Continuing Education for the Practicing Veterinarian.
- ACVS – American College of Veterinary Surgeons – BOAS resources.
- Cambridge BOAS Research Group – Functional Grading Scheme – vet.cam.ac.uk/boas.
- PuppaDogs. Heatstroke Risk Calculator and Ideal Weight & Weight Loss Calculator. puppadogs.com.
