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Bronchiolitis

Bronchiolitis is an acute wheezing-associated illness which occurs in early life, preceded by signs and symptoms of an upper respiratory infection. There is no clinical or laboratory feature that will distinguish infants who will have a single episode of bronchiolitis from those who will get bronchiolitis.

Epidemiology

Bronchiolitis occurs in all areas of the world with a highly seasonal prevalence. It occurs most frequently from mid-December to mid-March. Bronchiolitis is most serious in infants Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis in infants and young children, accounting for 50% of cases of bronchiolitis requiring hospitalization.

The frequency and severity of repeat RSV infections diminish with advancing age. Infants born prematurely, or with bronchopulmonary dysplasia (BPD), immunodeficiency or congenital heart disease are at especially high risk for severe RSV illness.

RSV is transmitted by direct contact with nasal secretions. Shedding of virus occurs 1 to 2 days before symptoms occur, and for 1 to 2 weeks afterwards.

Clinical Evaluation

Rhinorrhea and cough usually precedes the onset of bronchiolitis by 3-5 days. Cough deepens and becomes more frequent, appetite becomes reduced, and respiratory distress increases.

Fever is low-grade or absent. An exception is the association of otitis media, where temperatures can be as high as 104° F (40^° C). Tachycardia usually is present.

Nasal congestion is marked, and the tympanic membranes are often inflamed.

Cyanosis of the oral mucosa and nail beds may occur in severely ill infants. Restlessness and hyperinflation of the chest wall are signs of impending respiratory failure.

Hyperresonance of the chest wall may be present, and wheezing can be heard in most infants without auscultation. The wheezing sound is harsh and low in pitch, although severely affected.

An infant with symptoms of an upper respiratory illness for several days and wheezing during the peak RSV season usually will have bronchiolitis.

Chest X-rays. Bronchiolitis is characterized by a hyperinflated chest, flattening of the diaphragm, and patchy areas of atelectasis and/or infiltrates. There may be collapse of segments or lobes of the lung. Hyperinflation of the lung will distinguish bronchiolitis from viral pneumonia.

Arterial blood gases should be obtained to assess the severity of respiratory compromise. Carbon dioxide levels are commonly in the 30-35 mm Hg range. Respiratory failure is suggested by CO₂ values of 45-55 mm Hg. Arterial O₂ is an indicator of disease severity, especially when the O₂ tension drops below 66 mm Hg.

Heart rate and oxygen saturation values (<95%) are useful guidelines in decision making about hospitalization.

White blood cell count may be normal or elevated slightly, and the differential count may show neutrophilia.

Enzyme-linked immunosorbent assays (ELISA) of respiratory secretions for RSV are highly sensitive and specific.

Treatment

Outpatient management of bronchiolitis is appropriate for infants