Stridor in the Pediatric Patient

Worsening obstruction resulting in a decreased airway radius leads to increased turbulence to air flow, which is explained by Poiseuille’s law.^1,2,7 The resistance to airflow becomes inversely related to the fourth power of the radius, so even a small change in an already narrow pediatric airway can make a huge difference.⁵ In practice, this means 1 mm of mucosal edema will decrease the cross-sectional area of the airway by 75% and increase the resistance of airflow by a magnitude of 16 to 32 times depending on the level of turbulence.⁷The airway can be divided into extrathoracic and intrathoracic regions, separated by the vocal cords.¹³ Inspiratory stridor is typically due to extrathoracic obstruction and expiratory stridor is due to intrathoracic obstruction below the level of the cords. Biphasic stridor, however, may indicate a fixed obstruction at the level of the cords.^2,3,5,9

Acute Differentials

The pediatric patient is at high risk for respiratory decompensation when the upper airway is acutely compromised. The history, physical examination, and phases of stridor can help determine the underlying diagnosis and definitive treatment plan.

Acute Croup

Acute croup (laryngotracheitis) is a clinical diagnosis based on acute onset of barky cough and inspiratory stridor.¹ It is usually secondary to an infection, most commonly viral (parainfluenza virus), resulting in edema and increased secretions of the subglottic mucosa.⁷ The onset is typically preceded by upper respiratory illness (URI) symptoms, and is often worse at night or after waking from a nap.¹ The peak incidence is between ages 6 months to 3 years. While croup is a clinical diagnosis, an anteroposterior X-ray will often show a steeple sign.^7,10

Spasmodic Croup

Spasmodic croup is an atypical presentation usually seen in children 8 years or older without a preceding URI. Patients will wake up overnight with a harsh brass-like cough, stridor, and hoarse voice. The etiology is unclear, but often these patients have a history of atopy and respond in part to treatment with antihistamines.

Foreign Body Aspiration

All that is acutely stridulous is not croup. Stridor from foreign body aspiration is sudden in onset and children do not always present with a history suggestive of foreign body aspiration. Diagnosis requires a high index of suspicion because the event is often unwitnessed and typical patients are pre-verbal. The physical examination may reveal diminished air entry along with stridor. Diagnosis is made by obtaining an X-ray (lateral neck [Figure 1], lateral decubitus, or inspiratory/expiratory chest X-ray) or by bronchoscopy which is both diagnostic and therapeutic.^7,10 Remember to always think of foreign body aspiration in children with acute stridor who have neither fever nor antecedent URI symptoms.

Bacterial Tracheitis

Bacterial tracheitis should be suspected in toxic appearing children who present with respiratory distress and stridor but who have a poor response to nebulized epinephrine. It is typically seen in toddlers and school-aged children, and like a viral tracheitis, presentation can be preceded by either URI or fever.¹⁰ Stridor is caused by subglottic edema and mucopurulent secretions in the airway.^7,10 Infection is most commonly by S. aureus but initial antibiotic choice should be broad spectrum, and include a third-generation cephalosporin or beta-lactamase resistant penicillin.