Bronchiolitis

Etiology

The most common virus associated with bronchiolitis is the respiratory syncytial virus. However, over the years, many other viruses have been found to cause the same infection, and they include  the following:

• Human rhinovirus
• Coronavirus
• Human metapneumovirus
• Adenovirus
• Parainfluenza virus
• Human bocavirus

RSV accounts for the majority of cases, although in about 30% of infants, there may be 2 viruses present at the same time.

Risk factors include:

• Low birth weight (premature infants)
• Age less than 5 months
• Low socioeconomic population
• Airway anomalies
• Congenital immune deficiency disorders
• Parental smoking
• Crowded living environment
• Chronic lung disease (bronchopulmonary dysplasia)

Epidemiology

Bronchiolitis is most common in children less than 2 years of age. During the first year of life, the incidence has been reported to be about 11% to 15%. Depending on the severity of the infection, there are at least 5 hospitalizations for every 1000 children younger than 2 years of age. Bronchiolitis is classically a seasonal disorder that is most common during autumn and winter, but sporadic cases may occur throughout the year. Some of the risk factors that have been identified for severe infections include the following:

• History of prematurity (less than 32 to 34 weeks gestational age)
• Age younger than 3 months
• Neuromuscular disease
• Congenital heart disease
• Chronic lung illness
• Immunodeficiency

Pathophysiology

The clinical features of bronchiolitis are primarily due to airway obstruction and diminished lung compliance. The virus infects the epithelial cells in the airways and induces an inflammatory reaction that leads to ciliary dysfunction and cell death. The accumulated debris, edema of the airways, and narrowing of the airways due to the release of cytokines eventually lead to symptoms and lowered lung compliance. The patient then tries to overcome the decreased compliance by breathing harder. Typical features include:

• Air trapping
• Increased mucus production
• Atelectasis
• Labored breathing
• Decreased ventilation [4][5][6]

History and Physical

Once RSV is acquired, the symptoms of an upper respiratory tract infection appear and include a cough, fever, and rhinorrhea. Within 48 to 72 hours, the acute infection involving the lower airways will become evident. During the acute stage, the infant may develop small airway obstruction that leads to symptoms of respiratory distress. The physical exam will reveal crackles, wheezing, and rhonchi. The severity of respiratory distress may vary from infant to infant. Some infants may have mild disease with only tachypnea, but others may show severe retractions, grunting, and cyanosis. The course of the illness may last 7 to 10 days, and the infant may become irritable and not feed. However, most infants improve within 14 to 21 days, as long as they are well hydrated.

Evaluation

The diagnosis of bronchiolitis is made clinically. Blood work and imaging studies are only needed to rule out other causes. Ordering serology and other laboratory tests to identify the virus is only for academic purposes. The presence of the virus in the blood does not correlate with symptoms or the course of the disease. Laboratory assays in bronchiolitis are useful for epidemiological studies and have little practical application.

A chest x-ray should only be ordered if there is clinical suspicion of a complication such as pneumothorax or bacterial pneumonia. Urine cultures may be obtained in children who have no other source of infection and continue to spike temperatures. Concomitant urinary tract infections are known to occur in about 5% to 10% of cases.

Treatment / Management

The hallmark of management for children with bronchiolitis is symptomatic care. All infants and children who are diagnosed with bronchiolitis should be carefully assessed for adequacy of hydration, respiratory distress, and presence of hypoxia.[7][8][9][10](B2)

Children who present with mild to moderate symptoms can be treated with interventions like nasal saline, antipyretics, and a cool-mist humidifier. Those children with severe symptoms of acute respiratory distress, signs of hypoxia, and/or dehydration should be admitted and monitored. These children need aggressive hydration. The use of beta-adrenergic agonists like epinephrine or albuterol, or even steroids, has not been shown to be effective in children with bronchiolitis. Instead, these children should be provided with humidified oxygen and nebulized hypertonic saline. Ensuring that the infant is well hydrated is key, especially for those who cannot eat. Oxygen therapy to maintain saturations just above 90% is adequate.

Children who develop signs of severe respiratory distress may progress to respiratory failure. These children may require intensive care for mechanical ventilation or non-invasive support. A high-flow nasal cannula is an emerging modality of non-invasive support for children with bronchiolitis. Clinical trials are in progress.

Passive immunization against RSV is available with palivizumab for those who are at the greatest risk for severe illness. During the RSV season, this requires monthly injections of the drug, but this may not only be expensive but not also not practical for most infants.

Current recommendations by the American Academy of Pediatrics support the use of palivizumab during the first year of life for children with a gestational age less than 29 weeks, symptomatic congenital heart disease, chronic lung disease of prematurity, neuromuscular disorders that make it difficult to clear the airways, airway abnormalities, and immunodeficiency. Prophylaxis may be continued in the second year of life for children who require continued interventions for chronic lung disease of prematurity or those who remain immunosuppressed.

Differential Diagnosis

• Asthma
• Bacterial pneumonia
• Gastroesophageal reflux disease (GERD)
• Vascular ring
• Croup
• Foreign body aspiration
• Pertussis

Prognosis

Bronchiolitis is a self-limited infectious process. It is commonly managed with supportive care, hydration, fever control, and oxygenation. When the disorder is recognized and treated, the prognosis is excellent. The majority of children recover without any adverse effects. Past studies suggest that infants with severe bronchiolitis will develop wheezing in the future, but this has not been borne out by longitudinal studies.

About 3% of infants will require admission to the hospital, and the mortality rates vary from 0.5% to 7%. The large variation in mortality is because of different risk factors and the lack of availability of intensive care units in certain countries.

Complications

Complications include:

• Nosocomial infection in infants who are admitted
• Barotrauma is ventilation is required
• Arrhythmias induced by beta-agonists
• Nutritional deficiencies if there is persistent vomiting