Canis ISSN: 2398-2942

Brachycephalic obstructive airway syndrome (BOAS)

Synonym(s): Brachycephalic upper airway obstruction syndrome, BAOS, BAS, BUAOS

Contributor(s): Lynelle Johnson, Jill Sammarco, Gert ter Haar, Nai-Chieh Liu


  • Cause: congenital shortening of the bones of the skull when the soft tissues within the upper airway do not reduce in size proportionally; maldevelopment of the airway cartilages.
  • Signs: excessive panting, dyspnea, stertorous and stridorous breathing, respiratory effort, sleep-disordered breathing, exercise and heat intolerance, regurgitation/vomiting, cyanosis and collapse.
  • Diagnosis: breed, clinical signs, respiratory function tests, diagnostic imaging, endoscopic examination.
  • Treatment: medical treatment and surgical widening of the airways where possible.
  • Prognosis: good in mild-moderate cases with surgery.
    Print off the owner factsheet on Brachycephalic upper airway obstruction syndrome (BUAOS) Brachycephalic upper airway obstruction syndrome (BUAOS) to give to your client.



  • Syndrome comprising one or more of the following components:
    • Narrowing/stenosis of the external nares, obstruction of nasal vestibule by pronounced ventral alae, aberrant and hypertrophied nasal turbinates with increased mucosal contact point.
    • Nasopharyngeal narrowing and collapse.
    • Narrow pharyngeal dimensions, pharyngeal collapse, elongated soft palate Soft palate: elongated, macroglossia, and inflamed and extruded tonsils. 
    • Narrow laryngeal dimensions or laryngeal (cricoid) hypoplasia, everted larnygeal saccules Larynx: miscellaneous conditions Larynx: disease overview, collapse of laryngeal cartilages, redundant laryngeal soft tissues.
    • Hypoplastic trachea Trachea: hypoplasia, especially in the bulldog and bronchial collapse (especially in the Pug).
    • Skull base malformation (eg medialization of the pterygoid processes). 

Predisposing factors


  • Obesity Obesity.
  • Hot weather.
  • Exercise.
  • Excitement.
  • Stress.
  • Concurrent cardiac or pulmonary diseases.
  • Concurrent or secondary gastro-intestinal diseases with gastro-esophageal reflux.


  • Airflow through airways is impeded due to abnormal anatomy → noisy breathing and inability to take on board sufficient oxygen to meet increased demands imposed by exercise.
  • Restricted airflow → increased inspiratory effort → increased negative pressure within the upper airways leads to a high intrathoracic negative pressure which in turn leads to eversion of laryngeal saccules and airway collapse as well as a sliding hiatal hernia Hiatal hernia of the stomach. 
  • Increased respiratory effort may → upper airway edema → further obstruction to airflow. Regurgitation Regurgitation leads to acid reflux and increase in pharyngeal and laryngeal inflammation and thus a vicious cycle is set in motion.
  • Impeded airflow prevents adequate heat loss through panting so animals rapidly become hyperthermic Hyperthermia in hot weather, following exercise or during stress.
  • If the respiratory vicious cycle is left untreated, the dog may develop pulmonary edema, reduced arterial oxygen content, hypertension, and right-sided heart failure.  


  • Progressive.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Marchant T W, Dietschi E,  Rytz U et al (2019) An ADAMTS3 missense variant is associated with Norwich Terrier upper airway syndrome. PLoS Genetics
  • Mielke B, Lam R & ter Haar G (2017) Computed tomographic morphometry of tympanic bulla shape and position in brachycephalic and mesaticephalic dog breeds. Vet Radiol Ultrasound 58 (5), 552-558 PubMed. 
  • Liu N-C, Oechtering G U, Adams V J et al (2017) Outcomes and prognostic factors of surgical treatments for brachycephalic obstructive airway syndrome in 3 breeds. Vet Surg 46 (2), 271-280 PubMed.
  • Rutherford L, Beever L, Bruce M M & ter Haar G (2017) Assessment of Computed Tomography Derived Cricoid Cartilage and Tracheal Dimensions to Evaluate Degree of Cricoid Narrowing in Brachycephalic Dogs. Vet Radiol Ultrasound 58 (6), 634-646 PubMed.
  • Liu N-C, Adams V J, Kalmar L, Ladlow J F, Sargan D R et al (2016) Whole-body barometric plethysmography characterized upper airway obstruction in 3 brachycephalic breeds of dogs. JVIM 30(3), 853-865 PubMed doi: 10.1111/jvim.13933.
  • Heidenreich D, Gradner G, Kneissl S and Dupr√© G (2016) Nasopharyngeal dimensions from computed tomography of pugs and French bulldogs with brachycephalic airway syndrome. Vet Surg 45 (1), 83-90 PubMed.
  • Oechtering G U, Pohl S, Schlueter C et al (2016a) A novel approach to brachycephalic syndrome. 1. Evaluation of anatomical intranasal airway obstruction. Vet Surg 45 (2), 165-172 PubMed.  
  • Oechtering GU, Pohl S, Schlueter C & Schuenemann R (2016b) A novel approach to brachycephalic syndrome. 2. Laser-assisted turbinectomy (LATE). Vet Surg 45 (2), 173-181 PubMed
  • Pohl S, Roedler F S & Oechtering G U (2016) How does multilevel upper airway surgery influence the lives of dogs with severe brachycephaly? Results of a structured pre- and postoperative owner questionnaire. Vet J 210, 39-45 PubMed.
  • Kaye B M, Boroffka S A E B, Haagsman A N & ter Haar G (2015) Computed tomographic, radiographic and endoscopic tracheal dimensions in English bulldogs with grade 1 clinical signs of brachycephalic airway syndrome. Vet Radiol Ultrasound 56 (6), 609-616 PubMed
  • Rubin J A, Holt D E, Reetz J A &Clarke D L (2015) Signalment, clinical presentation, concurrent diseases, and diagnostic findings in 28 dogs with dynamic pharyngeal collapse (2008–2013). JVIM 29 (3), 815-821 PubMed.
  • Vilaplana Grosso F, Haar ter G & Boroffka S A E B (2015) Gender, weight, and age effects on prevalence of caudal aberrant nasal turbinates in clinically healthy English bulldogs: A computed tomographic study and classification. Vet Radiol Ultrasound 56 (6), 486-493 PubMed.
  • Schuenemann R & Oechtering G U (2014a) Inside the brachycephalic nose: intranasal mucosal contact points. JAAHA 50 (3), 149-158 PubMed
  • Schuenemann R and Oechtering G (2014b) Inside the brachycephalic nose: conchal regrowth and mucosal contact points after laser-assisted turbinectomy. JAAHA 50 (4), 237-246 PubMed.
  • Roedler F S, Pohl S & Oechtering G U (2013) How does severe brachycephaly affect dog’s lives? Results of a structured preoperative owner questionnaire. Vet J 198 (3), 606-610 PubMed
  • Palmer C (2012) Does breeding a bulldog harm it? Breeding, ethics and harm to animals. Animal Welfare 21 (2), 157-166 VetMedResource.
  • Grand  JG & Bureau S (2011) Structural characteristics of the soft palate and meatus nasopharyngeus in brachycephalic and non-brachycephalic dogs analysed by CT. JSAP 52 (5), 232-239 PubMed
  • White RN (2011) Surgical management of laryngeal collapse associated with brachycephalic airway obstruction syndrome in dogs. JSAP 53 (1), 44-50 PubMed.
  • Oechtering G U (2010) Brachycephalic syndrome – new information on an old congenital disease. Veterinary Focus 20 (2), 2-9 VetMedResource.
  • Brdecka D J, Rawlings C A, Perry A C & Anderson J R (2009) Use of an electrothermal, feedback-controlled, bipolar sealing device for resection of the elongated portion of the soft palate in dogs with obstructive upper airway disease. JAVMA 233 (8), 1265-1269 PubMed. 
  • Rooney N J (2009) The welfare of pedigree dogs: cause for concern. Journal of Veterinary Behaviour: Clinical Applications and Research 4 (5), 180–186 Journal of Veterinary Behaviour.
  • Huck J L, Stanley B J & Hauptman J G (2008) Technique and outcome of nares amputation (Trader's technique) in immature shih tzus. JAAHA 44 (2), 82-85 PubMed
  • Mehl M L, Kyles A E, Pypendop B H, Filipowicz DE & Gregory C R (2008) Outcome of laryngeal web resection with mucosal apposition for treatment of airway obstruction in dogs: 15 cases (1992–2006). JAVMA 233 (5), 738-742 PubMed.
  • Riecks T W, Birchard S J, Stephens J A (2007) Surgical correction of brachycephalic syndrome in dogs: 62 cases (1991-2004). JAVMA 230 (9), 1324-1328 PubMed.
  • Torrez CV and Hunt GB (2006) Results of surgical correction of abnormalities associated with brachycephalic airway obstruction syndrome in dogs in Australia. JSAP 47 (3), 150-154 PubMed.
  • Poncet C M, Dupre G P, Freiche V G et al (2005) Prevalence of gastrointestinal tract lesions in 73 brachycephalic dogs with upper respiratory syndrome. JSAP 46 (6), 273-279 PubMed.
  • Davidson E B, Davis M S, Campbell G A et al (2001) Evaluation of carbon dioxide laser and conventional incisional techniques for resection of soft palates in brachycephalic dogs. JAVMA 219 (6), 776-781 PubMed.
  • Lorison D, Bright R M & White R A S (1997) Brachycephalic airway obstruction syndrome - a review of 118 cases. Canine Pract 22 (5/6), 18-21 VetMedResource.
  • Clark G N & Sinibaldi K R (1994) Use of a carbon dioxide laser for treatment of elongated soft palate in dogs. JAVMA 204 (11), 1779-1781 PubMed.
  • Bright R M & Wheaton L G (1983) A modified surgical technique for elongated soft palate in dogs. JAAHA 19 (3), 288-292 VetMedResource.

Other sources of information

  • Oechtering G U (2017) Diseases of the nose, nasopharynx and sinuses. In: Textbook of Veterinary Internal Medicine. 8th edn, ed. S J Ettinger, E C Feldman &E Cote, pp 1059-1077. Elsevier, Philadelphia.
  • ter Haar G (2016a) Diseases of the nasal cavity and sinuses. In: Ear, Nose and Throat Diseases of the Dog and Cat. 1st edn, ed. R G Harvey & G ter Haar, pp 287-334. CRC Press, Taylor & Francis Group, London.
  • ter Haar G (2016b) Surgery of the nose. In: Ear, Nose and Throat Diseases of the Dog and Cat. 1st edn, ed. R G Harvey & G ter Haar, pp 449-474. CRC Press, Taylor & Francis Group, London.