Stridor is a high-pitched, harsh sound produced by turbulent
airflow through a partially obstructed airway. Both inspiratory
and expiratory stridor are associated with obstruction of the airway.
Two important physical principles influence the clinical presentation
of patients with stridor. As air is forced through a narrow tube,
it undergoes a decrease in pressure (the Venturi effect). This decrease
in lateral pressure causes the airway walls to collapse and vibrate,
generating stridor. The second physical principle is airway resistance.
Resistance is inversely proportional to the fourth power of the
airway radius. This translates into a 16-fold increase in resistance
when the radius is reduced by half. Even 1 mm of edema in
the normal pediatric subglottis reduces its cross-sectional area
by >50%. Thus, a small amount of inflammation can result
in significant airway obstruction in children.
Immediately assess the child with stridor, as respiratory compromise may
require maneuvers to secure the airway. The presence of stridor constitutes
a difficult airway, and advanced airway management may be necessary
(see Chapter 29, Pediatric Airway Management).
A thorough history and examination will often lead to a “working
diagnosis.” If time permits, ask about the time and events
surrounding the onset of stridor, the presence of fever, known congenital
anomalies, perinatal problems, prematurity, and previous endotracheal
The level of obstruction can often be identified on examination.
Partial obstruction of the upper airway at the nasopharynx and oropharyngeal levels produces
sonorous snoring sounds known as stertor. Obstruction of
the supraglottic region may cause inspiratory stridor or stertor.
Obstruction of the glottis and subglottic and tracheal areas often
cause both inspiratory and expiratory stridor. Consider airway
foreign body until proven otherwise if there is marked variation
in the pattern of stridor. The noise made by a child with
stridor is often interpreted as wheezing by parents unfamiliar with
stridor. Clarify what the parent means when the word “wheezing” is
used—whether the sound occurs when the child breathes in
or breathes out. The provider can imitate a stridor sound to help
ED diagnosis. The differential diagnosis of stridor depends upon the
child’s age (Table 119-1).
Table 119-1 Causes
of Stridor |Favorite Table|Download (.pdf)
Table 119-1 Causes
|Children <6 mo of age|
|Vocal cord paralysis|
|Children >6 mo of age|
|Foreign body aspiration|
An infant <6 months with a long duration of symptoms typically
has a congenital cause of stridor. The major causes are laryngomalacia, tracheomalacia, vocal
cord paralysis, and subglottic stenosis. Less common but important
considerations include airway hemangiomas and vascular rings and
slings. Stridor presenting in the first 6 months of life will often require
direct visualization of the airway through endoscopy or advanced
imaging. The timing of this evaluation (emergent or outpatient) is
dictated by the severity of symptoms and clinical suspicion.