While the grip of winter this year has been loosened in some locales, in others the fist is tight and will bring its annual upsurge of young patients who have croup or bronchiolitis. Croup targets the upper respiratory tract; bronchiolitis threatens the small and medium lower respiratory tract passages. Both illnesses are associated with significant morbidity and mortality in high-risk patients.
This article provides an update on the diagnosis and treatment of these 2 common pediatric diseases.
Croup, or acute laryngotracheobronchitis, is the most common infectious cause of sudden upper airway obstruction in children and of stridor in febrile children.1-3 Croup accounts for more than 15% of pediatric respiratory illnesses.4 Children aged 6 months to 6 years--especially boys--are affected most often: the peak incidence occurs during the second year of life. About 2% of all preschoolers have croup every year, and recurrence is common. Croup can develop at any time of the year, although it classically presents in late autumn and winter.
Although croup can be caused by bacteria (eg, Staphylococcus aureus, Haemophilus influenzae, Corynebacterium diphtheriae, and Mycoplasma pneumoniae) and atypical agents, most cases are viral. (This article will address viral croup only.) The leading cause of croup, isolated from more than 80% of positive cultures, is parainfluenza virus (types 1, 2, and 3).4 Other viruses that can cause croup include adenovirus, influenza A and B viruses, respiratory syncytial virus (RSV), and rubeola virus.4
The time and manner in which the child presents may yield general clues to the cause of the viral croup. For example, parainfluenza viruses predominate in the fall, whereas RSV croup peaks in the midwinter. The most severe illness is caused by influenza A virus infection.4
The pediatric airway is inherently predisposed toward obstruction.6 Because a child's airway is proportionally smaller than that of an adult, a given amount of luminal swelling reduces the airway diameter much more dramatically than it does in an adult. In infants, for example, 1 mm of subglottic edema decreases the cross-sectional area of the trachea by 50%.1 The narrowest portion of the pediatric airway is the subglottic region at the cricoid cartilage.
As with most respiratory infections, acute laryngotracheobronchitis begins in the nasopharynx and spreads through the respiratory tree. Diffuse inflammation, erythema, and edema develop in the tracheal walls and are most prominent in the subglottic region at the cricoid cartilage. Any swelling (mucosal and/or submucosal) in the region of the subglottic trachea encroaches on the airway, greatly restricting airflow and causing inspiratory stridor. The vocal cords become edematous and relatively immobile.
Croup typically starts with several days of nonspecific upper respiratory tract symptoms, such as rhinorrhea, pharyngitis, low-grade fever (temperature of 38ºC to 39ºC [100.4ºF to 102.2ºF]), and cough. Within 12 to 48 hours, the cough is harsh and barky (seal-like) and is accompanied by inspiratory stridor and hoarseness. A temperature that exceeds 40ºC (104ºF) and a toxic appearance are atypical and may indicate tracheitis or epiglottitis.
The great majority of children have mild symptoms, which tend to worsen at night and when the child becomes agitated. Symptoms typically peak by the third to fifth day of illness and last for 7 to 10 days. Airway obstruction develops in a small subset of children with croup. Severe hypoxia and death from croup are rare.
Spasmodic croup begins abruptly, generally occurs at night, and has a relatively mild course. The child may have had a previous respiratory tract infection. Between 1% and 5% of children hospitalized with croup require intubation for airway management.
The diagnosis of croup is clinical: the barking cough is distinctive and easily recognized by parents and clinicians. Nonetheless, it is still important to exclude other potentially life-threatening conditions, such as epiglottitis or foreign body ingestion, that require intervention.
Radiographs of the neck can help confirm the diagnosis of croup and exclude other causes of the croup syndrome. The anteroposterior view may demonstrate subglottic narrowing--the classic "steeple sign" of croup (Figure 1, left). Lateral films may demonstrate an overly distended hypopharynx.
Keep in mind that in approximately 50% of children with croup, the steeple sign is not visible on radiographs (giving a false-negative result). Moreover, subglottic narrowing can be present in children who do not have croup (giving a false-positive result). This suggests that radiographs should be used judiciously in the diagnosis of croup and are best reserved for children with atypical presentations.
Assessing disease severity
Croup scores are a subjective measurement of severity. The most commonly used is the Westley Score.2 Independent risk factors for respiratory failure include:
• Age younger than 6 months.
• Stridor at rest.
• Altered level of consciousness.
Airway management is the primary goal for children with croup. Hospitalization is indicated if any risk factors are present. Treatment has traditionally included mist therapy and inhaled epinephrine as well as corticosteroids.
Mist therapy. Mist has been widely used and is often the initial treatment before the child arrives in the emergency department (ED). While mist can soothe and moisten an inflamed airway, it can also increase respiratory distress by provoking anxiety and agitation in young children. Recent studies have questioned its efficacy.
Inhaled epinephrine. This is now standard therapy for children with moderate to severe croup. A dose of 0.5 µL of racemic epinephrine is equivalent to 5 µL/L of epinephrine (1:1000). Inhaled epinephrine works quickly and can dramatically reduce inspiratory stridor and retractions. However, as the effects of epinephrine wane – typically over 2 to 4 hours from time of administration – symptoms may begin to escalate and stridor, particularly when the child is at rest, may return. Recent studies suggest that the use of epinephrine does not mandate admission to the hospital and that children can be discharged after 2 to 4 hours of observation in the ED provided a corticosteroid has been administered and there is no return of stridor at rest or increased respiratory distress.
Children can be managed as outpatients if they are clinically stable, have no distress or stridor at rest, are not hypoxic, and have normal mentation. They also must have received a dose of dexamethasone.
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