Brachycephalic obstructive airway syndrome (BOAS)

• 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.

• Excessive panting, dyspnea.
• Stertorous and stridorous breathing.
• Respiratory effort. 
• Exercise and heat intolerance.
• Regurgitation and vomiting. 
• Sleep-disordered breathing. 
• Cyanosis and collapse.

• Respiratory distress or sudden collapse (particularly in hot weather) with cyanosis.
• May have almost total upper airway obstruction, which can lead to non-cardiogenic pulmonary edema Lung: pulmonary edema or aspiration pneumonia Lung: aspiration pneumonia, hyperthermia Hyperthermia, and can die rapidly without treatment.

• Clinical signs in severely affected cases can manifest at a young age.
• Many will present at 2-4 years of age.
• Clinical signs always progress over time without treatment.

• Highly prevalent breeds:
  • English bulldog Bulldog.
  • French bulldog French Bulldog and Pug Pug.
• Other reported breeds: Pekingese Pekingese , Shih Tzu Shih Tzu, Chihuahua Chihuahua, Pomeranian Pomeranian, Boston Terrier Boston Terrier, Japanese Chin Japanese Chin, Dogue de Bordeaux Dogue de Bordeaux, and Cavalier King Charles Spaniel Cavalier King Charles Spaniel.  

• Moderately expensive surgery required in cases with clinical signs. Where a full diagnosis workup with advanced diagnostic imaging is indicated, costs will be higher.

• 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). 

General

• 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.

• Breathing problems (eg excessive panting, dyspnea).
• Stertor, stridor, sleep disordered breathing (eg snoring, sleep apnea).
• Exercise and heat intolerance, cyanosis and collapse.
• Gastro-esophageal reflux, regurgitation, and vomiting.

• Exercise intolerance.

• Noisy breathing (snorting noise, ‘clicking sound’ when panting). 
• Loud snoring and disturbed sleeping. The dog may elevate the head when sleeping and/or hold a toy in the mouth to keep the mouth open while sleeping.
• Collapse Collapse.
• Signs may be exacerbated by exercise, excitement or hot weather.

• Gagging/retching cough.
• Regurgitation during exercise and/or excitement, or after eating/drinking 

• Stenotic nares with restricted nasal flaring.
• Stertorous or stridorous respiration with increased laryngeal noise on laryngeal auscultation, and inspiratory effort.  Many of these signs only present after exercise. A short (3 minutes) trotting test (a.k.a. respiratory functional grading) is recommended. 
• Cyanosis.
• Hyperthermia following exercise or stress due to inability to cool body temperature by panting.

Biochemistry

• Blood gas analysis Arterial blood gas sampling may show reduced arterial blood oxygen saturation in severe cases.
• Chronic hypoxia can lead to polycythemia Polycythemia: secondary.

Whole-body barometric plethysmography (WBBP)

• Respiratory parameters may show decreased or increased minute volume; prolonged inspiratory time; increased peak expiratory flow rate.  
• WBBP flow trace may show fixed-type obstruction or dynamic-type obstruction, or both.  
• A BOAS index can be calculated: a severity score from 0 (BOAS free) to 100% (severe BOAS). 

Endoscopic evaluation

• Oral examination and pharyngoscopy:
  • Pharyngeal narrowing (dorsoventral flattening of the pharynx, tonsillar protrusion, thickening of the base of the tongue, degree of pharyngeal mucosal edema, redundant pharyngeal soft tissue.
  • Length of the soft palate. Soft palate length can change dramatically under general anesthesia. Assessment during induction and before intubation is recommended.
• Laryngoscope Laryngoscopy:
  • Laryngeal dimensions (hypoplasia).
  • Function of larynx. Assessment during induction and before intubation is recommended; or respiratory stimulant such as Doxapram Doxapram may be applied.
  • Degree of collapse (eversion of laryngeal saccules, collapse of corniculate and cuneiform processes), and laryngomalacia.
  • Degree of edema of the laryngeal mucosa. 
  • Laryngeal granuloma. 
• Tracheobronchoscopy Tracheoscopy:
  • Tracheal hypoplasia Trachea: hypoplasia and/or collapse Trachea: collapse.
  • Bronchial collapse.
• Rhinoscopy Rhinoscopy and nasopharyngoscopy:
  • Narrowing of nasal vestibule (ventral alae).
  • Aberrant conchae (rostral and caudal turbinates); bony or mucosal, or combined, hypertrophy. Distorted and enlarged plica alaris.
  • Increased mucosal contact point.
  • Nasopharyngeal turbinate protrusion.
  • Nasopharyngeal cyst.  

Diagnostic imaging

• Thoracic and head radiography Radiography: thorax:
  • Hypoplastic trachea.  
  • Aspiration pneumonia. 
  • Severe hiatal hernia. 
• Computed tomography of the thorax, neck and head Computed tomography: head Computed tomography: nasal chamber:
  • Lower airway and the heart structure.
  • Similar findings as rhinoscopy in terms of aberrant nasal conchae. Mucosal hypertrophy of the turbinate and mucosal contact will not be detected accurately using CT.
  • Nasopharyngeal dimension.
  • Swollen lateral nasal glands. 
  • Soft palate length and thickness. 
  • Thickness of the tongue. 
  • Skull base abnormalities. 
  • Hypoplastic and collapsed trachea and bronchi. 
  • Stenotic nares and collapsed nasal vestibules. 
  • Hiatal hernia. 
  • Esophageal diverticula/ redundant esophageal mucosa.

• Lesions related to syndrome, eg elongated soft palate Soft palate: elongated.

• Airway foreign body Airway foreign body.
• Nasal and nasopharyngeal cyst, oronasal fistula, tumor.
• Laryngeal neoplasia Larynx: neoplasia.
• Tracheal neoplasia Trachea: neoplasia.
• Laryngeal paralysis Larynx: paralysis.
• Idiopathic laryngeal dysfunction. 
• Pulmonary neoplasia Lung: pulmonary neoplasia.
• Mass pressing on airway.
• Lung lobe torsion Lung: lobe torsion. 
• Rhinitis Rhinitis.  
• Laryngitis.  
• Epiglottic retroversion. 
• Cardiac disease.
• Traumatic airway disruption.

• Emergency stabilization of condition:
  • Sedation, eg acepromazine Acepromazine maleate (0.02-0.05 mg/kg) IV, IM or SQ or diazepam Diazepam (0.2 mg/kg) IV may be combined with oxymorphone (0.5 mg/kg) or butorphanol Butorphanol tartrate (0.3 mg/kg) IV, IM or SC.
  • Glucocorticoid (prednisolone Prednisolone 0.5 mg/kg BID or dexamethasone 1-2 mg/kg IV) administration to reduce laryngeal edema.
  • Tracheostomy Tracheostomy: temporary may be required in severely cyanotic patients.
  • Oral intubation may be considered during crisis as an option Endotracheal intubation.
  • Supplemental oxygen may be needed.
• Remove exacerbating factors:
  • Cage rest to reduce stress and excitement. Trazodone administration to reduce anxiety.
  • Cool patient if hyperthermic with fans, alcohol baths or cold water sprays.

• Weight management (ideal body condition score 4-5/9).
• Surgical correction of anatomical abnormalities amenable to surgical resection:
  • Correction of stenotic nares Stenotic nares enlargement and the enlarged and collapsed alar folds at nasal vestibules.  
  • Correction of oversized soft palate Soft palate: resection.
  • Correction of laryngeal collapse Larynx: laryngeal ventricle excision. Partial arytenoidectomy. 
  • Removal of protruded tonsils.  
  • Removal of the obstructive nasal turbinates (laser-assisted turbinectomy Laser-assisted turbinectomy (LATE)). 
• Medical management of GI signs.  

• Patients with clinical signs require surgical intervention as continued increased inspiratory effort will exacerbate severity of underlying pathology.
• Prognosis depends on the severity of underlying anomalies and the ability of the surgeon to correct them.
• With appropriate surgical correction, client education and maintaining an adequate body weight the prognosis can be good.
• Young, excessively underweight (usually due to frequent regurgitation), and dogs with advanced laryngeal collapse may have poorer prognosis.  

• Reduced respiratory noise.
• Improved exercise and heat tolerance.
• Improved oxygen saturation of blood.
• Improved sleep quality.  
• Reduced or resolved regurgitation.  

• Failure to diagnose and manage all elements of airway obstructive syndrome.
• Failure to diagnose and manage concurrent brachycephaly related diseases such as hiatal hernia with gastro-esophageal reflux.
• Inoperable lesions such as skull base malformation.  

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 doi.org/10.1371/journal.pgen.1008102.
• 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 Dupré 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.

• Cambridge BOAS Research Group: www.vet.cam.ac.uk/boas.