Stridor is a high pitched, harsh, vibratory noise caused by partial airway obstruction, which results in turbulent airflow. Stridor is typically heard on inspiration, but can also be heard on expiration and may also be biphasic. Inspiratory stridor suggests an obstruction above the glottis, due to collapse of soft tissues with negative pressure created during inspiration. Expiratory stridor indicates an obstruction in the lower trachea (intrathoracic trachea and lower bronchi). Biphasic stridor can indicate edema near the cricoid cartilage that surrounds the trachea and is indicative of a fixed caliber of airway unaffected by changes in intrathoracic pressure.

Stridor can be subdivided into acute and chronic causes.

1. Acute stridor is most commonly infectious in origin.

a. Croup (laryngotracheobronchitis) is the number one cause of acute stridor. Croup is most commonly caused by parainfluenza virus, but can also be caused by influenza virus type A or B, RSV, or rhinovirus. Croup usually affects children aged 6 months to 6 years, and is often preceded by a URI. Children with croup often present with a lowgrade fever and barking cough

b. Foreign body aspiration must be considered if symptoms begin abruptly and does not resolve with treatment.

c. Epiglottitis, most often caused by H. influenza type b (now a rare occurrence due to widespread vaccination with Hib vaccine).

d. Bacterial tracheitis- most often S. aureus Patient is usually toxic appearing

2. Chronic stridor in infants is most often caused by anatomic defects.

a. Laryngomalacia the number one cause of chronic stridor in infants less than 2 years. Laryngomalacia is upper airway obstruction caused by a defect in or delayed maturation of supporting structures of the larynx, causing a prolapse of the flaccid epiglottis during inspiration.

b. Bilateral vocal cord paralysis caused by CNS malformation, such as Arnold Chiari and increased intracranial pressure)

c. Acquired subglottic stenosis, post intubation or after trauma

d. Papillomas in the upper airways caused by vertical transmission of Human Papillomatous Viruses to newborns.

e. Vascular rings, aberrant innominate artery, tracheomalacia,

f. Stridor can be caused by rare anatomical malformations such as choanal atresia, lingual thyroid, thyroglossal duct cyst, macroglossia, micrognathia, hypertrophic tonsils, laryngeal webs or retropharyngeal or peritonsilar abscess.

Common findings that may accompany stridor

1. high-pitched crowing noise
2. "barking cough"
3. tachypnea
4. muffled voice. "Hot potato" voice
5. fever
6. hyperextension of neck
7. respiratory distress
8. URI symptoms
9. Symptoms may appear worse with crying because a larger air mass is inspired

1. Symptom complex, duration and acuity
2. History of URI
3. History of airway instrumentation (previous intubation)
4. Vaccination history ( H. influenza and influenza)
5. Foreign body- abrupt onset
6. Mother has history of HPV infection (venereal warts)
7. Physical findings

1. Inspiratory vs. expiratory vs. biphasic stridor
2. Fever
3. Presence of drooling or hyperextension of neck and unusual sitting position. Change of symptoms with positioning
4. Weak or muffled cry
5. Prolonged inspiratory/expiratory phase
6. Presence of cyanosis
7. Degree of distress
8. Facial deformities
9. Presence of hemangiomas elsewhere
10. Neck masses

1. AP and endolateral radiographs of the neck can assess adenoidal size, epiglottis, and trachea.
2. AP and lateral CXR to look for foreign body or pulmonary disease
3. Airway fluoroscopy
4. If stridor is persistent, direct exam of airway via flexible bronchoscope to look at area below cords
5. ABG’s or pulse oximetry to assess hypoxia

Treatment of stridor should be directed at underlying cause of disease. If severe airway obstruction or respiratory compromise is present, airway must be established with endotrachial intubation.

1. Stridor caused by viral croup without respiratory distress often responds to humidified air. Iif there is respiratory distress, nebulized racemic epinepherine and steroids will often be helpful.
2. Epiglottitis, now rare, is an emergent situation, as airway obstruction can progress rapidly. Intubation under anesthesia is warranted, and IV cefuroxime is given for empiric antibiotic coverage.
3. Laryngomalacia usually resolves by 18 months.
4. ENT referral if persistent stridor to assess the airway

1. Leung, K.C. and Chung, H. Diagnosis of Stridor in Children. American Family Physician. 1999: Vol 60, 40-48.
2. Cohen, L. Stridor and Upper Airway Obstruction in Children. Pediatrics in Review. 2000. Vol 21. 38.
3. Orenstein, D.M. Acute Inflammatory Upper Airway Obstruction. Nelson Textbook of Pediatrics. Philadelphia: W.B. Saunders, 2000: 1271-1272.