Definition

• Abnormally loud sounds that result from air passing through a narrowed nasopharynx, pharynx, larynx, or trachea.
• Discontinuous sounds heard without a stethoscope.
• Stertor-low-pitched snoring sound that usually arises from the vibration of flaccid tissue or fluid; usually arises from nasal or pharyngeal airway obstruction.
• Stridor-higher-pitched sounds that result when relatively rigid tissues are vibrated by the passage of air; result of partial or complete obstruction of the larynx or cervical trachea.

Pathophysiology

• Airway obstruction causes turbulence as air travels through a narrowed passage; with worsening obstruction or increasing airflow velocity, the amplitude of the sound increases as the tissue, secretion, or foreign body composing the obstruction vibrates.
• Obstruction sufficient to increase the work of breathing augments respiratory muscle effort and exacerbates turbulence; inflammation and edema of tissues in the region of the obstruction may develop, further reducing the airway lumen and further increasing the work of breathing, creating a vicious cycle.
• Obesity further increases respiratory effort and exacerbates airway obstruction.

Systems Affected

Respiratory

Genetics

• Brachycephalic syndrome heritable in many breeds.
• Inherited laryngeal paralysis-identified in Bouvier des Flandres, rottweilers, Siberian huskies, and Dalmatians.

Incidence/Prevalence

Common

Geographic Distribution

Worldwide

Signalment

Signs

• Change or loss of voice.
• Partial obstruction-produces an increase in airway sounds before producing an obvious change in respiratory pattern or gas exchange.
• Owners may indicate that the sound has existed for as long as several years.
• Breath sounds audible from a distance without a stethoscope-suspect narrowing of upper airway.
• Nature of the sound-ranges from abnormally loud to obvious fluttering to high-pitched squeaking, depending on the degree of airway narrowing.
• May note increased respiratory effort and paradoxical respiratory movements (chest wall collapses inward during inspiration and springs outward during expiration) when the effort is extreme; respiratory motions often accompanied by obvious postural changes (e.g., abducted forelimbs, extended head and neck, and open-mouth breathing).

Causes

• Brachycephalic airway syndrome (stenotic nares, elongated soft palate, everted laryngeal saccules, laryngeal collapse).
• Laryngeal paralysis-inherited or acquired.
• Laryngeal neoplasia-benign or malignant.
• Granulomatous/inflammatory laryngitis.
• Tracheal collapse, stenosis, obstruction, neoplasia, foreign body.
• Nasopharyngeal polyp, stenosis, foreign body.
• Acromegaly.
• Neuromuscular dysfunction or trauma.
• Anesthesia or sedation-only if predisposing anatomy exists.
• Cystic Rathke cleft.
• Cleft soft palate.
• Aplasia of soft palate.
• Redundant pharyngeal mucosal folds.
• Soft palate mass.
• Edema or inflammation of the palate, pharynx, and larynx (including everted mucosal lining of the laryngeal ventricles)-secondary to coughing, vomiting or regurgitation, turbulent airflow, upper respiratory infection, and hemorrhage.
• Secretions (e.g., pus, mucus, and blood) in the airway lumen-acutely after surgery; a normal conscious animal would cough out or swallow them.

Risk Factors

• High ambient temperature or humidity.
• Fever.
• High metabolic rate-as occurs with hyperthyroidism or sepsis.
• Exercise.
• Anxiety or excitement.
• Any respiratory or cardiovascular disease that increases ventilation.
• Turbulence caused by the increased airflow can lead to swelling and worsen the airway obstruction.

Differential Diagnosis

• Systematically auscultate over the nose, pharynx, larynx, and trachea to identify the point of maximal intensity of any abnormal sound and to identify the phase of respiration when it is most obvious.
• Important to identify the anatomic location from which the abnormal sound arises and to seek exacerbating causes (see “Risk Factors”; e.g., a chronic airway obstruction may become manifest when the patient is exposed to extremely high ambient temperatures).
• Must differentiate sounds of pharyngeal, laryngeal, and tracheal narrowing from sounds arising elsewhere in the respiratory system.
• Nasal and tracheal narrowing and severe or extensive narrowing of the bronchi-can cause increased respiratory sounds.
• If the sound persists when the patient opens its mouth, a nasal cause can virtually be ruled out.
• If the owner describes a change in voice, the larynx is the likely abnormal site.

Other Laboratory Tests

Arterial blood gas occasionally indicated; hypoxia and hypoventilation occur with prolonged severe obstruction.

Imaging

• Lateral radiographs of the head and neck-may help identify abnormal soft tissues of the airway (e.g., elongated soft palate or a nasal polyp); limited use for identifying laryngeal paralysis, although experienced radiographers can identify abnormally dilated or swollen laryngeal saccules; cartilaginous destruction is suggestive of neoplasia or granulomatous laryngitis; may detect external masses compressing the upper airway.
• Radiography and fluoroscopy-important for assessing the cardiorespiratory system; rule out other or additional causes of respiratory difficulty; such conditions may add to an underlying upper airway obstruction, causing a subclinical condition to become clinical.
• Digital radiology is preferred for best detail.
• Ultrasound can be used to assess laryngeal structure and function, can also be used to document cervical tracheal collapse but air is a poor acoustic window.
• Computed tomography can be used to provide additional anatomic detail.

Diagnostic Procedures

Appropriate Health Care

• Inpatient management required for surgical treatment.
• Closely monitor effects of sedatives; sedatives can relax the upper airway muscles and worsen the obstruction; be prepared with emergency methods for securing the airway if complete obstruction occurs. Diazepam preferred.
• Extreme airway obstruction-attempt an emergency intubation; if obstruction prevents intubation, emergency tracheotomy or passage of a tracheal catheter to administer oxygen may be the only available means for sustaining life; a tracheal catheter can briefly sustain oxygenation while a more permanent solution is sought.

Nursing Care

• Treatment requires removal of obstruction, supplemental oxygen is variably helpful.
• Intravenous fluids may be required, particularly if hyperthermia develops from increased work of breathing.
• Active cooling measures (ice packs in axilla and groin region, alcohol on foot pads, chilled IV fluids) helpful in alleviating hyperthermia but not indicated for fever.

Activity

Keep patient cool, quiet, and calm-anxiety, exertion, and pain lead to increased ventilation, potentially worsening the obstruction.

Diet

• NPO if anesthesia is planned.
• Avoid obesity that worsens respiratory effort.

Client Education

Inform client that the patient can make the transition from being a noisy breather to having an obstructed airway in a few minutes or even seconds.

Surgical Considerations

• Laryngoscopy and bronchoscopy for foreign body retrieval and biopsy of laryngeal region and tracheal lumen. Use of small balloon catheters passed beyond the foreign body prior to expansion may be useful in removing some objects.
• Take particular care when inducing general anesthesia or when using sedatives in any patient with upper airway obstruction.
• Surgery-indicated to obtain a diagnosis through biopsy with histopathology, to manage obstruction while awaiting histopathology results or resolution of inflammation/infection (e.g., tracheotomy), or to resolve disease by excision, correction of obstructive lesion, and removal of foreign bodies.

Drug(s)

• Medical approaches-appropriate only if the underlying cause is infection, edema, inflammation, or hemorrhage; anatomic or neurologic causes are not amenable to medical treatment.
• Steroids-may be indicated if edema or inflammation is thought to be an important contributor; effect with intravenous administration should be apparent in approximately 1 hour. Single dose may be sufficient or a tapering dose might be required. Inflammatory laryngitis often requires higher doses administered over a longer dosing schedule with taper of the dose according to resolution of clinical signs.

Precautions

Sedatives, analgesics, and anesthetics-avoid excessive suppression of laryngeal movement and respiratory suppression to avoid aspiration in animals with laryngeal disease.

Patient Monitoring

Respiratory rate and effort need to be closely monitored. When owner chooses to take an apparently stable patient home, or if continual observation is not feasible, inform client that complete obstruction could occur.

Prevention/Avoidance

Advise client to avoid exercise, high ambient temperatures, and extreme excitement.

Possible Complications

Serious complications may occur without therapy to relieve the obstruction; these include airway edema, pulmonary edema (may progress to life-threatening acute lung injury), and hypoventilation; may require tracheotomy and/or artificial ventilation.

Expected Course and Prognosis

• Varies with underlying cause.
• Even with surgical treatment, some degree of obstruction may remain for 7–10 days due to swelling.

Associated Conditions

Peripheral neuropathy often associated with laryngeal paralysis.

Synonyms

Snoring

See Also

• Acromegaly-Cats
• Brachycephalic Airway Syndrome
• Hypothyroidism
• Laryngeal Diseases
• Myasthenia Gravis
• Nasal and Nasopharyngeal Polyps
• Tracheal and Airway Collapse

Client Education Handout Available Online