Definition

Partial upper airway obstruction in brachycephalic breeds of dogs and cats caused by any of the following: stenotic nares, overlong soft palate, everted laryngeal saccules, and laryngeal collapse. Hypoplastic trachea can also be present and worsen respiratory distress.

Pathophysiology

• In normal dogs, the upper airway accounts for 50–70% of total airway resistance. Brachycephalic breeds have increased upper airway resistance due to stenosis of nares, aberrant formation of nasal conchae, and presence of nasopharyngeal turbinates. Skull bones are shortened in length but normal in width, and soft tissues are not proportionately reduced, resulting in redundant tissue and narrowed air passages.
• Increased airway resistance leads to more negative intra-airway pressures-may result in secondary eversion of laryngeal saccules, further elongation of palate, and laryngeal collapse.
• Recruitment of pharyngeal dilator muscles (sternohyoid) becomes necessary to maintain airway patency. Sleep apnea may occur secondary to relaxation of these muscles.

Systems Affected

• Respiratory-respiratory distress, hypoxemia, hypercarbia, hyperthermia, aspiration pneumonia, non-cardiogenic pulmonary edema from airway obstruction.
• Cardiovascular-cardiovascular collapse if complete airway obstruction or severe hyperthermia occurs.
• Gastrointestinal-may be reluctant to eat or drink, increased airway resistance can exacerbate hiatal hernia, gastroesophageal reflux, and esophagitis.

Genetics

• Brachycephalic head shape–inherited defect in development of skull bones perpetuated by selective breeding.

Incidence/Prevalence

• Dogs-common in brachycephalic breeds.
• Cats-less commonly severe enough to require treatment.

Geographic Distribution

Worldwide

Signalment

Signs

Causes

• Inherited or congenital defects in conformation.
• Elongated soft palate->90% of surgical cases in dogs.
• Stenotic nares-about 50% of dogs. Most common defect in cats.
• Aberrant formation of rostral and caudal nasal conchae.
• Presence of nasopharyngeal turbinates (20% of dogs).
• Laryngeal disease-everted laryngeal saccules (>50% of dogs) and/or laryngeal collapse (∼10% of dogs).

Risk Factors

• Breed.
• Obesity-worsens airway obstruction, associated with poorer outcome postoperatively, and may contribute to gastroesophageal reflux resulting in aspiration pneumonia.
• Excitement and/or warm, humid weather-increased panting can lead to airway edema, further compromise of the lumen, and hyperthermia.
• Exercise-dogs are often exercise-intolerant due to airway compromise and hypoxia.
• Sedation-relaxation of muscles of pharynx and palate can cause complete airway obstruction.
• Respiratory infection or concurrent pulmonary disease-will cause further respiratory compromise.
• Endocrine disease (hypothyroidism and hyperadrenocorticism)-could worsen weight gain and cause excessive panting.

Differential Diagnosis

• Foreign bodies of nasopharynx, larynx, or trachea.
• Infection-upper respiratory infection, nasopharyngeal abscess.
• Neoplasia obstructing the nasopharynx, glottis, larynx, or trachea.
• Laryngeal paralysis.
• Pharyngeal mucocoele.
• Nasopharyngeal polyp or cyst.

CBC/Biochemistry/Urinalysis

CBC-usually normal, but polycythemia can occur with chronic hypoxia, and leukocytosis if concurrent infection or severe stress.

Other Laboratory Tests

• Arterial blood gas-to diagnose respiratory acidosis and hypoxemia, and response to oxygen supplementation.
• Pulse oximetry-to diagnose hypoxemia.

Imaging

Diagnostic Procedures

Appropriate Health Care

• Surgery recommended for patients with significant clinical signs or to prevent progressive respiratory dysfunction.
• Emergency presentation in severe respiratory distress requires rapid intervention including O₂supplementation, cautious use of antianxiety medication.
• If hyperthermic, cool via convective losses by wetting patient with cool water and placing fan to blow over them. Administer IV fluids, up to a shock rate if extremely hyperthermic (T°>106°F [41°C]).
• If complete airway obstruction, immediate orotracheal intubation and/or temporary tracheostomy is indicated.
• Dexamethasone can be administered (0.1 mg/kg IV) to reduce inflammation.

Nursing Care

• Patients require 24-hour monitoring because of risk of acute airway obstruction and death.
• Monitor respiratory rate, effort, heart rate, pulse quality, mucous membrane color, capillary refill time, temperature, and other physical parameters before and after surgery.
• Pulse oximetry and arterial blood gases, depending on severity of condition.
• Administer IV fluids at maintenance rate and minimize handling and stress.
• O₂therapy and cooling as necessary.

Activity

Usually self-limited

Diet

• If overweight, weight loss is recommended.
• For obese, stable patients, weight loss is recommended prior to surgery.

Client Education

• Avoidance of risk factors is critical.
• Inform owners that dogs with brachycephalic airway syndrome are at increased anesthetic risk, especially if obese, or have cardiac disease or aspiration pneumonia.
• Inform owners that surgery often improves but does not normalize airway.

Surgical Considerations

• Evaluation for elongated soft palate performed under general anesthesia when patient is stable.
• Temporary tracheostomy can be placed to facilitate exposure or to treat airway obstruction.
• Stenotic nares are corrected by resection of a wedge of the dorsolateral nasal cartilage and planum. Hemorrhage is controlled with pressure followed by closure of the surgical wound with 3or 4sutures of 3–0or 4–0absorbable suture material.
• Elongated soft palate is resected using scissors, carbon dioxide laser, or a bipolar sealing device. Remove only enough to allow contact of the center of the soft palate with the tip of the epiglottis.
• Sacculectomy performed by grasping tissue with Allis tissue forceps and trimming all mucosal tissue with curved scissors.
• Severe laryngeal collapse might require cricoarytenoid and thyroarytenoid caudolateralization or permanent tracheostomy.

Drug(s)

• Dexamethasone given for 12–24h pre-or postoperatively at 0.1 mg/kg IV q12h to reduce edema and inflammation.
• Broad-spectrum antibiotics indicated if aspiration pneumonia present until culture and sensitivity results are obtained.
• Omeprazole 0.7 mg/kg q24h, cisapride 0.2 mg/kg q8h, and magnesium hydroxide 1 mL/kg after meals or sucralfate 0.5–1 g q12h for dogs with concurrent esophagitis, gastritis, and/or duodenitis.

Contraindications

Overuse of steroids can lead to panting, weight gain, and gastrointestinal ulceration, which can all exacerbate signs of brachycephalic airway syndrome.

Precautions

Sedation for relief of anxiety, excitement, or fear should be used with caution because of risk of upper airway obstruction with muscle relaxation.

Patient Monitoring

Postoperatively, 24-hour monitoring to observe for airway swelling and obstruction that may require temporary tracheostomy.

Prevention/Avoidance

• Selection by breeders for dogs without severe conformational changes-difficult because breed standards encourage these.
• Avoid risk factors, particularly weight gain.

Possible Complications

• Hyperthermia and heat stroke.
• Aspiration pneumonia.
• Death in about 10% of patients from airway disease.
• The most common postoperative complication is airway swelling and obstruction within the first 24hours, may necessitate temporary tracheostomy.
• Continued respiratory difficulty after corrective surgery.
• Excessive resection of palate resulting in nasal aspiration of food contents due to inability to close pharynx during swallowing.

Expected Course and Prognosis

• Prognosis is good for improvement in breathing (80% have good to excellent results) but airway is still far from normal.
• Prognosis better for dogs other than English bulldogs and for dogs that have correction of both stenotic nares and elongated soft palate.
• Without surgery, prognosis is poor due to continued progression of acquired components of brachycephalic airway syndrome.
• Life-long avoidance of risk factors recommended.

Associated Conditions

• Aspiration pneumonia
• Heat stroke
• Hiatal hernia
• Hypoplastic trachea

Age-Related Factors

Older dogs may have a worse outcome postoperatively but most have some improvement.

Pregnancy/Fertility/Breeding

Enlarged abdomen and pressure on the diaphragm in the pregnant bitch can further compromise respiratory function by decreasing tidal volume.

Internet Resources

http://www.acvs.org/AnimalOwners/HealthConditions/SmallAnimalTopics/BrachycephalicSyndrome/

Client Education Handout Available Online