Stridor is a high-pitched, harsh sound produced by turbulent airflow through a partially obstructed airway. Both inspiratory and expiratory stridor are associated with airway obstruction. As air is forced through a narrow tube, it undergoes a decrease in pressure (the Venturi effect). The decrease in lateral pressure causes the airway walls to collapse and vibrate, generating stridor. Airway 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%. A small amount of inflammation can result in significant airway obstruction in children.
Immediately assess the child with stridor, because stridor indicates a difficult airway, and advanced airway management may be necessary (see chapter 111, "Intubation and Ventilation in Infants and Children"). 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, called 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 on the child's age (Table 123-1).
TABLE 123-1Causes of Stridor |Favorite Table|Download (.pdf) TABLE 123-1 Causes of Stridor
Children <6 mo of age
Vocal cord paralysis
Children >6 mo of age
Foreign body aspiration
STRIDOR IN CHILDREN <6 MONTHS OLD
An infant <6 months old 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.
Laryngomalacia accounts for 60% of all neonatal laryngeal problems and results from a developmentally weak larynx. Collapse occurs with each inspiration at the epiglottis, aryepiglottic folds, and arytenoids. Generally, stridor worsens with crying and agitation but often improves with neck extension and when the child is prone. Laryngomalacia usually manifests shortly after birth, which is a key diagnostic feature, and generally resolves by age 18 months old. In many cases, the tracheal support structures are similarly affected, resulting in laryngotracheomalacia. Symptom exacerbations may occur with upper respiratory infections or increased work of breathing from any cause. Definitive diagnosis can ...