Stridor
Stridor is a high-pitched respiratory sound, often inspiratory, that raises concern for upper-airway narrowing. It is produced by turbulent airflow through a narrowed segment of the airway above or at the level of the vocal cords.
The timing of stridor within the respiratory cycle provides diagnostic information:
- Inspiratory stridor — suggests obstruction at or above the vocal cords (supraglottic): epiglottitis, croup, foreign body in the pharynx, angioedema, peritonsillar abscess
- Expiratory stridor — suggests obstruction below the vocal cords (subglottic): tracheal stenosis, foreign body in the trachea
- Biphasic stridor (both inspiratory and expiratory) — suggests a fixed obstruction at the level of the vocal cords or subglottis: severe croup, vocal cord paralysis, subglottic stenosis
Stridor is a clinical sign, not a diagnosis. Its presence indicates that the upper airway is significantly narrowed — typically to less than 50% of its normal diameter before stridor becomes audible. This means that by the time stridor is heard, the obstruction is already substantial.
The clinical urgency of stridor depends on context. Stridor in a child with a barking cough and low-grade fever suggests croup and may respond to nebulized epinephrine and dexamethasone. Stridor in an adult with lip swelling and urticaria after a medication exposure suggests anaphylaxis and requires immediate epinephrine and preparation for possible intubation. Stridor that is worsening, associated with drooling or inability to swallow, or accompanied by signs of respiratory failure (accessory muscle use, cyanosis, altered mental status) demands immediate airway intervention.
Stridor should be distinguished from wheeze, which is typically expiratory and indicates lower-airway narrowing. Both are sounds of turbulent airflow through a narrowed passage, but their anatomical location and clinical implications differ.