Contributors: Lynelle Johnson, Jill Sammarco, Gert ter Haar, Nai-Chieh Liu
Species: Canine | Classification: Diseases
- 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:
- 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).
- Obesity Obesity.
- Hot weather.
- 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.
- 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.
- Hyperthermia following exercise or stress due to inability to cool body temperature by panting.
- 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).
- 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:
- 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.
- 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.
Gross Autopsy Findings
- 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.
- Epiglottic retroversion.
- Cardiac disease.
- Traumatic airway disruption.
Initial Symptomatic Treatment
- 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.
Expected Response to Treatment
- Reduced respiratory noise.
- Improved exercise and heat tolerance.
- Improved oxygen saturation of blood.
- Improved sleep quality.
- Reduced or resolved regurgitation.
Reasons for Treatment Failure
- 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.
- Recent references from PubMed and VetMedResource.
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- 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.
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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.
Other Sources of Information
- Cambridge BOAS Research Group: www.vet.cam.ac.uk/boas.