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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 intubation.

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

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.


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