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
| Save Table
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.
Laryngomalacia, the most common cause of congenital
stridor, 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 and generally
resolves by age 18 months old. Symptom exacerbations may occur with
upper respiratory infections or increased work of breathing from
any cause. Diagnosis can often be made with flexible fiberoptic laryngoscopy.
Surgical intervention may be required if a child suffers from failure
to thrive, apnea, or pulmonary hypertension. Surgical management,
when required, is based on the pattern of supraglottic collapse. In
many cases, the tracheal support structures are similarly affected, leading
to a diagnosis of laryngotracheomalacia.
The next most common cause of neonatal stridor is vocal cord
paralysis. This can be congenital or acquired. Unilateral vocal
cord paralysis is more common and presents with feeding problems,
stridor, hoarse voice, and cry changes. Children with bilateral
cord paralysis often have a normal voice associated with stridor
and dyspnea. These children are more likely to present with cyanosis
and apneic episodes. Flexible nasolaryngoscopy is the referenced
standard for making the diagnosis of vocal cord paralysis. Endotracheal
intubation can be difficult in patients with bilateral cord paralysis.
Needle cricothyroidotomy and subsequent tracheotomy may be required
to secure the airway.
Subglottic stenosis may be acquired or congenital and is diagnosed
when there is a narrowing of the laryngeal lumen. Congenital stenosis
is usually diagnosed in the first few months of life when the patient
is noted to have persistent inspiratory stridor.
Mild cases may present later in childhood with recurrent or persistent
croup. Prolonged endotracheal intubation in premature babies is
the most common cause of acquired subglottic stenosis. Treatment
is based on the severity of the stenosis. In most cases, symptoms
from subglottic stenosis resolve by a few years of age.
Hemangiomas are benign congenital tumors of endothelial cells
or vascular malformations that can occur anywhere on the body (80% are
located above the clavicles), including the airway where they can
cause obstruction and stridor. Hemangiomas typically enlarge throughout
the first year of life, may not be noticed at birth, and tend to
spontaneously regress by age 5 years old. A thorough examination
of the skin of an undressed infant is an important aspect of the
evaluation of stridor in the first 6 months of life, as hemangiomas
may be multiple, and findings externally may be a clue to the presence
of an airway hemangioma. Definitive diagnosis requires airway
visualization through endoscopy. Although most hemangiomas spontaneously
regress, large malformations and those causing significant respiratory
symptoms may require treatment with steroids, laser, or surgery.
Vascular rings and slings are rare congenital anomalies of the
aortic arch and pulmonary artery in which abnormal embryonic development
leads to anomalous vessels that can compress the trachea or esophagus.
Examples include a double- or right-sided aortic arch. As with other
congenital causes of stridor, symptoms are often present from birth
or early in the first month of life and may be progressive and exaggerated
during intercurrent upper respiratory infections; difficulty with
feeding may also occur if the esophagus is compressed. As these
anomalies are rare, a high index of suspicion is required for diagnosis.
Chest x-ray may reveal subtle narrowing or anterior compression
of the trachea on ...