A 9-month-old infant is brought to the emergency department because of a 1-hour history of a barky cough and difficulty breathing, which followed a 2-day history of rhinorrhea and low-grade fever. He does not appear toxic, but is tachypneic, and has inspiratory stridor and suprasternal retractions. He is not drooling and has no change in voice. A dose of nebulized epinephrine is administered while awaiting the results of his neck x-ray. The frontal view of an x-ray of the soft tissues of the neck shows narrowing of the subglottic space (Steeple sign) (Figure 30-1). A diagnosis of croup is made and the infant is given a dose of dexamethasone orally. Thirty minutes later, his stridor and retractions have resolved.

Upper airway obstruction refers to blockage of any portion of the airway above the thoracic inlet or the extrathoracic airway. It is one of the most daunting emergencies faced by a physician and, if not promptly diagnosed and managed, can progress to hypoxia and can lead to cardio-respiratory arrest and irreversible brain damage. Stridor, suprasternal retractions, and change of voice are the sentinel signs of upper airway obstruction.

• Upper airway obstruction is often referred to as extra-thoracic airway obstruction.

• Croup is also known as laryngotracheobronchitis.

• Epiglottitis is used synonymously with supraglottitis.

• Bacterial tracheitis is also known as bacterial laryngotracheobronchitis or pseudomembranous croup.

• Upper airway obstruction is one of the most common life-threatening emergencies in children, accounting for up to 15 percent of visits to the emergency department.¹

• Croup is the most common infection that causes acute upper airway obstruction and has an annual incidence of 18 per 1,000 children in the US; children between the ages of 6 months and 4 years are primarily affected, with a peak incidence of 60 per 1,000 among children 1 to 2 years of age. Although sporadic cases occur throughout the year, croup is epidemic in early fall and winter.²

• The incidence of epiglottitis has decreased dramatically, since the introduction of the conjugated Haemophilus influenzae type b vaccine, from 41 cases per 100,000 children in 1987 to 1.3 per 100,000 in 1997.^2,3

• Bacterial tracheitis has an estimated incidence of approximately 0.1 cases per 100,000 children per year and has a peak incidence in fall and winter. Although it affects all age groups, it occurs more frequently in children between the ages of 6 months and 8 years. Retropharyngeal abscess is more common in young children, with the vast majority of cases occurring in patients younger than 6 years of age.²

• Peritonsillar abscess is usually a disease of older children and adolescents.

• Foreign body aspiration is a common pediatric problem that has the potential to cause partial or complete airway obstruction. The majority of cases involve the toddler age group. Common foods aspirated are peanuts, popcorn, hotdog, candy, and grapes.

• Although upper airway obstruction can occur at different levels of the airway, obstruction at the level of the larynx and subglottis assumes the greatest importance because the subglottis is the narrowest portion; therefore, even small lesions can become symptomatic.

• The subglottic region is completely encircled by the cricoid cartilage and cannot expand in diameter. Should inflammation and edema develop, the subglottic airway caliber is substantially reduced as it contains loosely attached connective tissue.

• Narrowing of the airway has an exponential effect on airflow. Poiseulle’s law for laminar airflow states that ΔP = (Q) (8 ηl/πr4) where ΔP is the pressure gradient between 2 ends of a tube (airway); Q is the volume of air passing through the tube per unit time (or velocity of flow); r is the radius; β is the viscosity of the medium; and l is the length. Rearranging this equation gives us the determinants of the resistance to laminar airflow, which is ΔP/Q = (8 ηl/π;r4). However, when airway diameter is reduced, airflow becomes turbulent and the resistance to turbulent flow is inversely proportional to the fifth power of the radius of the lumen of the airway. Thus, a small decrease in the radius of the airway results in a marked increase in resistance to airflow and work of breathing.

• Table 30-1 shows the common causes of acute upper airway obstruction. The etiology of upper airway obstruction differs by age group with congenital abnormalities predominating in neonates, and infectious agents accounting for the majority of cases in infancy and early childhood.