What does inspiratory stridor indicate?

Inspiratory Stridor: Clinical Significance and Diagnostic Approach

Inspiratory stridor primarily indicates obstruction of the upper airways, most commonly at the level of the larynx or above, and requires prompt evaluation to identify the underlying cause and prevent respiratory failure. 1

Pathophysiology and Clinical Significance

Inspiratory stridor is a high-pitched respiratory sound caused by turbulent airflow through narrowed upper airways. The timing of stridor provides important diagnostic clues:

• Inspiratory stridor: Typically indicates obstruction at the supraglottic or glottic level (larynx or above)
• Expiratory stridor: Usually suggests obstruction at or below the glottic level
• Biphasic stridor: Often indicates severe or fixed airway obstruction 2

Common Causes by Age Group

In Infants

• Laryngomalacia: Most common cause of chronic inspiratory stridor in infants (60-70% of cases) 1, 3
• Vocal cord paralysis: Third most common congenital laryngeal anomaly 1
• Congenital anomalies: Laryngoceles, saccular cysts, laryngeal webs/atresia, laryngotracheal stenosis, laryngeal/tracheal clefts, congenital neoplasms 1
• Chiari malformation: Rare cause that can present with intermittent vocal cord paralysis 4

In Children and Adults

• Acute infections: Croup, epiglottitis, bacterial tracheitis
• Foreign body aspiration
• Exercise-induced laryngeal dysfunction (EILD): Including vocal cord dysfunction (VCD), exercise-induced laryngeal prolapse, and exercise-induced laryngomalacia 1
• Post-extubation stridor: Due to laryngeal edema 5
• Functional stridor: Non-organic cause requiring exclusion of anatomic pathology 6

Diagnostic Approach

Immediate Assessment

1. Evaluate severity of respiratory distress: Assess for increased work of breathing, retractions, cyanosis, or altered mental status
2. Determine timing of stridor: Inspiratory, expiratory, or biphasic
3. Assess acuity: Acute vs. chronic presentation

Key Diagnostic Tests

• Flexible endoscopy: Gold standard for diagnosis, allowing visualization of laryngeal structure and function during both inspiration and expiration 1
• Flow-volume loops: May show flattening or truncation of the inspiratory portion in cases of VCD 1
• Continuous laryngoscopy during exercise: For suspected exercise-induced laryngeal disorders 1

Important Diagnostic Distinctions

• Exercise-induced laryngeal dysfunction vs. Exercise-induced bronchoconstriction:
  • EILD: Stridor occurs and peaks during exercise, resolves within ~5 minutes of stopping, primarily affects inspiration
  • EIB: Dyspnea occurs after exercise, peaks 5-20 minutes after stopping, primarily affects expiration 1

Management Principles

Management depends on the underlying cause:

• Laryngomalacia: Most cases can be managed conservatively with resolution by 2 years of age; severe cases may require supraglottoplasty 3
• Post-extubation stridor: Systemic corticosteroids as first-line treatment, followed by nebulized epinephrine if symptoms persist 5
• Exercise-induced laryngeal disorders: Speech therapy and addressing psychophysiologic stress; β2-agonists are ineffective 1
• Functional stridor: Supportive treatment after excluding organic causes 6

Important Clinical Considerations

• Up to 68% of children with stridor may have abnormalities below the epiglottis, making complete airway evaluation important 1
• Stridor in older children is rare (outside of post-intubation) and always warrants endoscopic evaluation 1
• Failure to respond to asthma management is a key feature suggesting EILD that may be mimicking asthma attacks 1
• Preparation for airway management should be readily available when evaluating patients with stridor, as respiratory failure can develop rapidly 5

When to Refer for Specialist Evaluation

Bronchoscopy/laryngoscopy is indicated in:

• Severe or persistent stridor
• Stridor associated with hoarseness
• Stridor leading to oxygen desaturation or apnea
• Stridor in older children (rare and concerning) 1