What is Stridor?
Stridor is a high-pitched respiratory sound caused by turbulent airflow through narrowed upper airways, typically reflecting obstruction at the level of the larynx or trachea. 1, 2, 3
Acoustic Characteristics
- Stridor is a loud, musical sound of constant pitch that differs from wheezing by its extrathoracic origin and characteristic high-pitched quality 2, 4, 5
- The sound results from turbulent airflow through anatomically narrowed airways, creating audible vibrations 3, 5
Clinical Significance by Timing
The phase of respiration during which stridor occurs provides critical diagnostic information about the level of obstruction: 6
- Inspiratory stridor typically indicates supraglottic or glottic obstruction (above or at the vocal cords) 3, 5
- Expiratory stridor suggests obstruction at or below the glottic level 3
- Biphasic stridor (both inspiratory and expiratory) indicates severe upper airway obstruction or fixed obstruction 3
Most Common Causes
In Infants and Children
- Laryngomalacia is the most common congenital laryngeal anomaly and the most frequent cause of persistent stridor in children, characterized by weakening of supraglottic structures 1, 6, 4
- Vocal cord paralysis is the third most common congenital laryngeal anomaly producing stridor in infants, usually resulting from central nervous system anomalies 1, 6
- Other congenital causes include laryngoceles, saccular cysts, laryngeal webs and atresia, laryngotracheal stenosis, and congenital neoplasms such as hemangiomas 1, 6
- Foreign body aspiration is an important acquired cause of acute stridor 6, 7
In Adults and Post-Procedural Settings
- Laryngeal edema following extubation is a major cause, with laryngeal pathology present in more than 75% of mechanically ventilated patients 1
- Laryngospasm represents an exaggerated protective reflex triggered by airway irritation, blood, or secretions, causing signs of upper airway obstruction including stridor 1
- Post-intubation complications including vocal cord injury, crico-arytenoid joint dysfunction, and tracheomalacia 1
Critical Clinical Context
Stridor always indicates significant airway narrowing and warrants immediate evaluation, as the differential ranges from benign self-limited conditions to life-threatening emergencies 2, 3
- In infants, stridor or noisy breathing is the most common indication for flexible bronchoscopy, as it usually reflects upper airway obstruction 1
- Concomitant abnormalities below the epiglottis are found in up to 68% of cases, making complete airway evaluation essential 1, 6
- In older children, stridor is rare but always indicates need for airway endoscopy unless clearly related to recent endotracheal intubation 1, 6
When Stridor Requires Urgent Intervention
Immediate assessment is required when stridor is associated with: 6
- Severe or persistent symptoms
- Associated hoarseness
- Oxygen desaturation or apnea
- Signs of respiratory distress including accessory muscle use, retractions, agitation, or SpO2 < 90%