Asthma is the most common chronic disease and the most frequent reason for hospitalization of children in the United States. The primary pathologic event is airway inflammation causing recurrent episodes of wheezing, dyspnea and cough associated with airflow obstruction that is variably reversible. The most common triggers are viral infections (often with fever), allergens (animals, dust, mold, pollen), environmental irritants (tobacco smoke, ozone), cold air, and exercise. Acute exacerbations may progress to unresponsive airway obstruction (status asthmaticus), respiratory failure and death and demand immediate treatment calibrated to severity.
The patient with an acute exacerbation may present with cough, wheezing, shortness of breath, chest tightness and/or chest pain. Cough is as frequent a manifestation as wheezing, and wheezing may be absent if airway obstruction is severe. Rales or rhonchi may be present but are usually due to atelectasis and thus are localized and clear with bronchodilator treatment. Tachypnea is a sensitive sign, and together with accessory muscle use is an accurate measure of severity. Elevation of pulsus paradoxus, decreased aeration on chest auscultation, and patient fatigue are potential signs of impending respiratory failure.
Hypoxemia is usually mild (SpO2 > 92%) and due to V/Q mismatch, which may worsen during initial treatment with bronchodilators for a period of 1 to 2 hours requiring oxygen therapy. If available, end-tidal CO2 (ETCO2) by capnometry should be monitored during severe exacerbations. Hypocapnia is expected early in the course of an asthma exacerbation, thus a normal or minimally elevated ETCO2 may be a sign of impending ventilatory failure.
Diagnosis and Differential
The diagnosis of bronchospasm is made clinically. The chronic diagnosis of asthma is rarely made in the ED, as spirometry, the criterion standard, is not routinely available in the ED. Although peak expiratory flow is often recommended for children > 5 years, it frequently underestimates the severity of airway obstruction. If available, FEV1 is the preferred measure of severity, with percent predicted level defining severity: ≥ 40% correlates with mild-moderate airway obstruction, and < 40% correlates to a severe exacerbation.
Because viral infections are the most common precipitant of asthma exacerbations in children, and because fever is a common associated sign, fever alone does not indicate the need for a chest radiograph. It may be considered for infants and young children with a first episode of wheezing to exclude anatomic abnormalities or foreign body. For others, a radiograph is indicated when localized findings (rales or decreased breath sounds) do not resolve with bronchodilator treatment or when there is concern for possible pneumothorax (pain or significant hypoxia) or foreign body. The pediatric respiratory assessment measure (PRAM) is one of the few severity scores that has been validated, and each ED should have a preferred score to facilitate severity assessment and communication amongst providers.
The differential diagnosis of wheezing in infants and children ...