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Stridor is characterized as a high-pitched, harsh, monophonic sound produced by turbulent airflow through a partially obstructed airway.1 Both inspiratory and expiratory stridor are associated with airway obstruction. As air is forced through a narrow tube, it undergoes an increase in speed and a decrease in pressure (Bernoulli’s principle). The decrease in lateral pressure causes the walls of the airway to temporarily collapse and vibrate, generating this stridulous sound. Hagen-Poiseuille’s law shows that resistance to laminar airflow increases markedly with small decreases in the airway’s radius.2 A small amount of inflammation can result in significant airway obstruction in children.

R (resistance) = 8 •η (viscosity) • l (length)/π • r4 (radius)

Immediately assess a child with stridor, as stridor indicates a difficult airway, and advanced airway management may be necessary (see Chapter 113, “Intubation and Ventilation in Infants and Children”). A thorough history and examination will often lead to a “working diagnosis.” Inquire about the time and events surrounding the onset of stridor, the presence of fever, known congenital anomalies, cardiac abnormalities, perinatal complications, prematurity, neonatal intensive care unit interventions, and previous endotracheal intubation or instrumentation.3

The level of obstruction can often be identified on examination. Partial obstruction of the upper airway at the nasopharynx and/or oropharyngeal level produces sonorous sounds, called stertor. Obstruction above the true vocal cords is generally indicative of inspiratory stridor, whereas expiratory stridor is characterized by obstruction below the true vocal cords. Biphasic stridor suggests obstruction at the level of the true vocal cords.4

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 differential diagnosis of stridor depends on the child’s age (Table 126-1).

TABLE 126-1Causes of Stridor


An infant <6 months old with a long duration of symptoms often 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, vascular rings, and slings. Stridor presenting in the first 6 months of life will often require direct airway visualization through endoscopy or advanced imaging. The timing of this evaluation (emergent or outpatient) is dictated by the severity of symptoms and clinical suspicion.

Laryngomalacia accounts for 60% of ...

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