Stridor: Signs, Symptoms, and Clinical Presentation
Stridor is a high-pitched, audible respiratory sound caused by turbulent airflow through a partially obstructed upper airway, most commonly heard during inspiration and reflecting obstruction at the supraglottic or glottic level 1.
Key Clinical Features
Acoustic Characteristics
- Inspiratory stridor: Indicates supraglottic or glottic obstruction (most common)
- Expiratory stridor: Suggests obstruction at or below the glottis
- Biphasic stridor: Reflects severe upper airway obstruction or subglottic involvement 2
Associated Signs of Respiratory Distress
When evaluating stridor, look specifically for these accompanying features 3:
- Accessory muscle use
- Tracheal tug
- Sternal, subcostal, and intercostal retractions
- Agitation or restlessness (may indicate worsening obstruction)
- Absence of signs as obstruction worsens (ominous finding)
Age-Specific Presentations
In Infants (most common age group):
- Stridor or noisy breathing is the most common indication for airway evaluation 1
- Laryngomalacia is the most frequent cause of persistent stridor, typically developing in the first 1-2 months of life 4, 5
- Symptoms are positional and usually do not interfere with growth initially
- Look for worsening after feeding, cyanosis, or inadequate weight gain (indicates severe disease) 4
In Older Children:
- Stridor is rare but always warrants endoscopy if not due to recent intubation 1
- Viral croup becomes the predominant acute cause, presenting with the classic triad:
- Barking cough
- Hoarse voice or cry
- Inspiratory or biphasic stridor 4
Critical Red Flags Requiring Urgent Evaluation
Proceed immediately to further investigation if any of these are present 1:
- Severe or persistent symptoms
- Associated hoarseness
- Oxygen desaturation or apnea
- Failure to thrive
- Altered consciousness
- Dysphagia (suggests vascular anomaly or compressive pathology) 6
- Stridor that fails to respond to standard croup treatment (consider alternative diagnoses) 4, 7
Timing and Context
Acute vs. Chronic Stridor
The single most important diagnostic distinction is determining whether stridor is acute or chronic 4:
Acute stridor (sudden onset):
- Viral croup (most common)
- Foreign body aspiration (look for sudden onset during eating/playing, absence of fever)
- Bacterial tracheitis
- Epiglottitis
- Anaphylaxis
Chronic stridor (present from birth or developing over weeks/months):
- Laryngomalacia (most common congenital cause)
- Vocal cord paralysis (third most common congenital anomaly)
- Subglottic hemangiomas
- Laryngeal webs, stenosis, or clefts 1
Exercise-Induced Stridor
Inspiratory stridor with throat tightness during maximal exercise that resolves within 5 minutes suggests exercise-induced laryngeal dysfunction (EILD), not exercise-induced bronchoconstriction 8. This is a critical distinction because:
- EILD does not respond to beta-2 agonists
- Symptoms occur during exercise (not after, as with EIB)
- More common in young adult female elite athletes
- Requires laryngoscopy during exercise for definitive diagnosis
Common Pitfalls
Mistaking persistent stridor for recurrent croup: If a child has been treated multiple times for "croup" without resolution, consider anatomic abnormalities or vascular compression 6
Missing concomitant lower airway abnormalities: Up to 68% of children with upper airway stridor have abnormalities below the epiglottis—examine both upper and lower airways when possible 1
Assuming all stridor in infants is benign laryngomalacia: While laryngomalacia is most common, always evaluate for severe disease indicators before adopting watchful waiting 4
Overlooking foreign body aspiration: Look for sudden onset during eating/playing, unilateral wheezing, and absence of preceding upper respiratory symptoms 9, 7