Introduction:

Bronchiolitis is one of the most common acute lower respiratory infections in infants, primarily during the winter and spring seasons. It predominantly affects infants aged between 1 and 6 months but can also be seen in children up to 2 years old. The primary causative agent is the respiratory syncytial virus (RSV), though other viruses, such as parainfluenza, adenovirus, and influenza viruses, can also contribute.

Protection against RSV is largely mediated by IgG3 antibodies, which have a short half-life and are transferred in minimal amounts across the placenta. As a result, infants do not receive significant protection from maternal antibodies. However, since colostrum contains high levels of secretory IgA antibodies, breastfeeding has been shown to reduce the risk of hospitalization due to bronchiolitis2.

Pathogenesis

Bronchiolitis results from inflammation of the bronchiolar mucosa, leading to edema, bronchiolar spasm, mucus plug formation, and accumulation of cellular debris. Due to the inverse relationship between airway resistance and airway radius, even minor narrowing of the bronchioles leads to a significant increase in airflow resistance, making breathing difficult3.

• Airflow restriction occurs during both inhalation and exhalation.

• Expiratory airflow is particularly affected due to partial bronchiolar collapse, leading to air trapping and lung hyperinflation (emphysema).

• Complete obstruction can cause atelectasis (lung collapse) as the trapped air is gradually absorbed.

• Severe cases may result in impaired ventilation, hypoxemia, and respiratory acidosis.

Clinical Presentation and Diagnosis

The onset of bronchiolitis typically resembles a mild upper respiratory infection. After a few days, symptoms worsen, including1,4:

• High fever

• Rapid breathing (tachypnea) and respiratory distress

• Lower intercostal and suprasternal retractions (in severe cases)

• Cyanosis (bluish discoloration of skin due to lack of oxygen)

• Prolonged expiration with wheezing

• Fine crackles (crepitations) and rhonchi on auscultation

• Diminished breath sounds in severe cases

• Increased chest diameter and hyperresonance due to air trapping

• Displacement of liver and spleen due to lung hyperinflation

Diagnostic Tests:

• Chest X-ray: Shows hyperinflation, lung infiltrates, and a depressed diaphragm5.

• Blood tests: Leukocyte counts may be normal or slightly elevated.

• Rapid RSV test: Nasopharyngeal aspirate can be tested to confirm RSV infection.

Disease Progression and Prognosis

Bronchiolitis is typically self-limiting, with symptoms resolving within 3–7 days. However, about 1% of severely ill infants may develop respiratory failure, which can be fatal6. Additionally, studies suggest that one in four children with bronchiolitis may later develop bronchial asthma7 

Differential Diagnosis

Bronchiolitis symptoms overlap with several other respiratory conditions, requiring careful differentiation1,4:

• Bronchial Asthma: Less common in children under one year of age. Typically, there is a family history of asthma, recurrent episodes, and a better response to bronchodilators.

• Congestive Heart Failure: Suspected if there is cardiomegaly (enlarged heart), tachycardia, raised jugular venous pressure (JVP), hepatomegaly (enlarged liver), and peripheral edema.

• Foreign Body Aspiration: Presents with a history of choking, localized wheezing, and signs of airway obstruction.

• Bacterial Pneumonia: Distinguished by high fever, pronounced lung sounds, and fewer obstructive symptoms compared to bronchiolitis.

Treatment and Management

1. Supportive Care:

• Mild cases can be managed at home in a humidified environment.

• Infants with worsening respiratory distress or feeding difficulties should be hospitalized.

• Moist oxygen therapy is crucial, even if cyanosis is absent.

• Severely ill infants may require oxygen concentrations of up to 60% to maintain oxygen saturation above 92%4.

2. Medications:

• Antibiotics are not recommended, as bronchiolitis is caused by viruses1.

• Ribavirin, an antiviral drug, is not routinely used but may benefit infants with congenital heart disease, chronic lung disease, or immunodeficiency. It is delivered via nebulization (16 hours/day for 3–5 days)3.

• Bronchodilators, steroids, and epinephrine have limited effectiveness in treating bronchiolitis. However, if an infant shows improvement, bronchodilator therapy may be continued every 4–6 hours7.

• Inhaled hypertonic saline has shown benefits in select patients, but routine use is not recommended8.

3. Advanced Respiratory Support:

• Continuous positive airway pressure (CPAP) or mechanical ventilation is necessary for severe respiratory failure5.

• Extracorporeal membrane oxygenation (ECMO) is considered in life-threatening cases when other interventions fail6.

Conclusion

Bronchiolitis is a common and self-limiting viral infection that primarily affects infants. While mild cases resolve with supportive care, severe cases require oxygen therapy and, in extreme situations, mechanical ventilation. Preventive measures such as breastfeeding and avoiding viral exposure during peak seasons can significantly reduce the risk of severe bronchiolitis.

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References

1. Ghai OP. Essential Paediatrics. 10th ed. New Delhi: CBS Publishers; 2022.

2. Hockenberry MJ, Wilson D. Wong’s Essentials of Paediatric Nursing. 11th ed. St. Louis: Elsevier; 2021.

3. Chen L, Shi M, Deng Q, Liu W, Li Q, Ye P, et al. A multi-center randomized prospective study on the treatment of infant bronchiolitis with interferon α1b nebulization. PLoS One. 2020 Feb 21;15(2):e0228391. doi: 10.1371/journal.pone.0228391.

4. Smyth RL, Openshaw PJ. Bronchiolitis. Lancet. 2006 Dec 23;368(9532):312–22. doi: 10.1016/S0140-6736(06)69274-7.

5. Meissner HC. Viral bronchiolitis in children. N Engl J Med. 2016 Jan 28;374(5):179–89. doi: 10.1056/NEJMra1413456.

6. Florin TA, Plint AC, Zorc JJ. Viral bronchiolitis. Lancet. 2017 Jul 22;389(10065):211–24. doi: 10.1016/S0140-6736(16)30951-5.

7. Kneyber MCJ, van Heerde M, Twisk JW, Plotz FB. Respiratory syncytial virus bronchiolitis and recurrent wheeze: a systematic review. Lancet Infect Dis. 2015 Aug;15(8):834–45. doi: 10.1016/S1473-3099(15)00097-7.

8. Zhang L, Mendoza-Sassi RA, Wainwright C, Klassen TP. Nebulized hypertonic saline for acute bronchiolitis in infants. Cochrane Database Syst Rev. 2017 Jun 22;6(6):CD006458. doi: 10.1002/14651858.CD006458.pub4..

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