Bronchiolitis

Most cases of bronchiolitis are caused by:

• Respiratory syncytial virus (RSV)

• Rhinovirus

• Parainfluenza virus type 3

Less frequent causes are influenza viruses A and B, parainfluenza viruses types 1 and 2, human metapneumovirus, adenoviruses, and Mycoplasma pneumoniae.

Risk factors for more severe disease include younger age, gestational age at birth (ie, preterm), low birth weight, comorbidities (eg, chronic lung disease), and exposure to tobacco smoke and secondhand smoke (1).

The virus spreads from the upper respiratory tract to the medium and small bronchi and bronchioles, causing epithelial necrosis and initiating an inflammatory response. For RSV, infection and cellular damage ensue when the virus binds to ciliated epithelial cells of the bronchioles and alveolar pneumocytes via surface glycoproteins F and G (1). The developing edema and exudate result in partial obstruction, which is most pronounced on expiration and leads to alveolar air trapping. Complete obstruction and absorption of the trapped air may lead to multiple areas of atelectasis, which can be exacerbated by breathing high inspired oxygen concentrations.

Typically, an affected infant has symptoms of upper respiratory infection. Some infants have progressively increasing respiratory distress characterized by tachypnea, retractions, and a wheezy or hacking cough.

Infants < 2 months of age and infants born prematurely may present with recurrent apneic spells followed by resolution of apnea and onset of more typical symptoms and signs of bronchiolitis over 24 to 48 hours. Signs of distress may include circumoral cyanosis, deepening retractions, and audible wheezing. Fever is usually, but not always, present. Infants initially appear nontoxic and are not in distress early in the course of the disease, despite tachypnea and retractions, but may become increasingly lethargic as the infection progresses. Hypoxemia is the rule in more severely affected infants.

Dehydration may result from vomiting and decreased oral intake. With fatigue, respirations may become more shallow and ineffective, leading to respiratory acidosis. Auscultation reveals wheezing, prolonged expiration, and, often, fine crackles.

More than half of children 3 to 18 months old have accompanying acute otitis media (1).

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Wheezing

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Crackles

• Exclusion of other causes

• Pulse oximetry

• Chest radiograph for more severe cases

• Testing for respiratory syncytial virus (RSV) in seriously ill children using rapid antigen or molecular diagnostic tests

The diagnosis of bronchiolitis is suspected by history, physical examination findings, and occurrence of the illness as part of an epidemic (1). Differential diagnoses must be excluded.

Patients suspected of having bronchiolitis should undergo pulse oximetry to evaluate oxygenation. No further testing is required for mild cases with normal oxygen levels, but in cases of hypoxemia and severe respiratory distress, a chest radiograph supports the diagnosis and typically shows hyperinflated lungs, depressed diaphragm, and prominent hilar markings. Infiltrates resulting from atelectasis and/or RSV pneumonia may be present; RSV pneumonia is relatively common among infants with RSV bronchiolitis.

RSV rapid antigen testing or nucleic acid amplification testing (NAAT, available as single or multiplex PCR assays) may be done on nasal washings, nasal aspirates, or nasal swabs and is diagnostic but not generally recommended for uncomplicated bronchiolitis (1, 2). Testing for RSV may be reserved for patients with illness severe enough to require hospitalization because it may guide isolation and bed assignment decisions. The sensitivities and specificities of available testing methods are high (> 80 and 90% for rapid antigen assay and > 90% and up to 99% for NAAT) (2). Other laboratory testing is nonspecific and is not routinely indicated.

• Supportive therapy

• Oxygen supplementation as needed

• IV hydration as needed

• Sometimes bronchodilators

The treatment of bronchiolitis is usually supportive, and most children can be managed at home with hydration and comfort measures (1). Patients who are at risk of developing severe disease should be hospitalized.

Indications for hospitalization include (2):

• Accelerating respiratory distress

• Hypoxia (especially if initial oxygen saturation was < 90%)

• Apnea by history

• Ill appearance (eg, cyanosis, lethargy, fatigue)

• Inadequate oral intake or dehydration

Other considerations for hospitalization include age < 2 months (2). Additionally, children with an underlying disorder such as cardiac disease, immunodeficiency, or chronic lung disease (eg, bronchopulmonary dysplasia), which puts them at high risk of severe or complicated disease, also should be considered for hospitalization.

In hospitalized children, 30 to 40% oxygen delivered by nasal cannula, tent, or face mask is usually sufficient to maintain adequate oxygen saturation > 90%. Endotracheal intubation is indicated for severe recurrent apnea, hypoxemia unresponsive to oxygen therapy, or CO2 retention or if the child cannot clear bronchial secretions. High-flow nasal cannula therapy, continuous positive airway pressure (CPAP) therapy, or both are often used to avoid intubation in patients who are at risk of respiratory failure.

Hydration may be maintained with frequent small feedings of clear liquids. For sicker children, fluids should be given IV initially, and the level of hydration should be monitored by urine output and specific gravity and by serum electrolyte determinations.

Bronchodilators are not uniformly effective, but a substantial subset of children may respond with short-term improvement. This is particularly true of infants who have wheezed previously. Bronchodilator use has not been found to reduce rates of hospital or intensive care unit admission, emergency department return visits, or ventilation rates (3).

Inhaled or systemic glucocorticoids are not recommended for the first episode of bronchiolitis. Glucocorticoid therapy is reasonable for patients > 12 months of age with recurrent episodes of wheezing, especially if there is clinical concern for asthma, because there may be overlap between the clinical symptoms of bronchiolitis and virally induced exacerbation of asthma.

Ribavirin, an antiviral medication active in vitro against respiratory syncytial virus (RSV), influenza, and measles, has not been found to be beneficial when administered to patients with uncomplicated RSV infection (Ribavirin, an antiviral medication active in vitro against respiratory syncytial virus (RSV), influenza, and measles, has not been found to be beneficial when administered to patients with uncomplicated RSV infection (4), and its routine use for the treatment of RSV bronchiolitis is not recommended. However, there may be a role for the use of ribavirin in immunocompromised children with severe RSV infection (see Treatment of RSV).

Antibiotics are not indicated in the treatment of severe bronchiolitis unless a secondary bacterial infection (a rare sequela) occurs.

The approach to prevention of RSV is discussed separately (see Prevention of RSV for indications).

The prognosis for bronchiolitis is usually excellent. Most children recover in 3 to 5 days without sequelae, although wheezing and cough may continue for 2 to 4 weeks. In the United States, mortality is < 0.1% when medical care is timely and adequate (1). Mortality rates are higher in children in resource-limited regions of the world (2).

An increased incidence of asthma is suspected in children who have had bronchiolitis in early childhood, but the association is controversial because the children who later develop asthma may be more severely affected by RSV and therefore are more likely to seek medical attention.