Residency · Residency · Pediatrics

Bronchiolitis

Overview

Bronchiolitis is the most common lower respiratory tract infection in infants under 12 months of age. Peak incidence occurs between 2 and 6 months, with the peak season running from November through March in the Northern Hemisphere. RSV accounts for 50-80% of cases, with other causative agents including rhinovirus, metapneumovirus, parainfluenza, adenovirus, and bocavirus. Bronchiolitis is the leading cause of infant hospitalization in the developed world, with approximately 3% of all infants hospitalized during their first year. The illness is self-limited in most cases, with symptoms resolving in 7-10 days though cough may persist for 2-3 weeks.

Pathophysiology

Viral infection of the bronchiolar epithelium causes necrosis, ciliary dysfunction, and peribronchiolar inflammation. The resulting mucus plugging, submucosal edema, and bronchospasm (which plays only a minor role) lead to small airway obstruction. This produces air trapping, ventilation-perfusion mismatch, and atelectasis. Infants are particularly susceptible due to their small airway caliber, immature immune response, and obligate nasal breathing.

Clinical Presentation

The illness begins with a 2-3 day prodrome of rhinorrhea, cough, and low-grade fever. A progressive phase follows with increased work of breathing, tachypnea, wheezing, and crackles. Nasal congestion and feeding difficulty are often the most clinically significant features. Apnea may be the presenting sign, particularly in former premature infants and neonates under 1 month. Peak severity typically occurs on days 3-5 of illness.

Risk Factors for Severe Disease

Infants at highest risk for severe bronchiolitis include those born prematurely (before 32 weeks), those under 3 months of age, those with chronic lung disease (BPD), hemodynamically significant congenital heart disease, immunodeficiency, neuromuscular disease affecting airway clearance, and secondhand smoke exposure.

<image>Clinical progression timeline of bronchiolitis showing prodromal phase (days 1-3 with URI symptoms), peak severity (days 3-5 with increased work of breathing, hypoxemia, and feeding difficulty), and recovery phase (days 5-10), with indicators for when hospitalization is most commonly required</image>

Diagnosis

Bronchiolitis is a clinical diagnosis, and no routine laboratory or imaging studies are needed. Chest X-ray is not recommended routinely and is associated with increased antibiotic use without clinical benefit; it should be considered only if clinical deterioration suggests pneumonia or complication. Viral testing (RSV rapid antigen, PCR multiplex) may guide isolation and cohorting decisions but does not change management. Blood gases, CBC, and blood cultures are not indicated for typical bronchiolitis.

Management: Evidence-Based Supportive Care

What Works

Nasal suctioning with bulb suction or nasopharyngeal suctioning provides airway clearance and is particularly critical before feeds. Supplemental oxygen is indicated for sustained SpO2 below 90% (per the AAP 2014 guideline threshold); brief intermittent desaturations during sleep are common and do not require intervention. IV fluids or nasogastric feeds are used for infants unable to maintain adequate oral intake (typically less than 50% of normal intake). Continuous pulse oximetry is used for hospitalized patients on supplemental oxygen, with intermittent checks once oxygen is discontinued.

High-Flow Nasal Cannula (HFNC)

HFNC delivers heated, humidified oxygen/air blend at 2 L/kg/min (maximum approximately 20-25 L/min in infants). It provides a low-level CPAP effect (approximately 2-5 cm H2O), washes out dead space, and reduces work of breathing. It is increasingly used as rescue therapy for infants failing low-flow oxygen and may reduce the need for ICU admission and intubation (though evidence quality is moderate). It is not recommended as first-line therapy for all bronchiolitis.

What Does NOT Work (Evidence Against Routine Use)

Bronchodilators (albuterol, epinephrine) provide no consistent benefit and may cause tachycardia; the AAP recommends against routine use. A one-time trial of albuterol is reasonable in older infants with a family history of asthma or atopy, but it should be discontinued if no objective improvement is observed. Systemic corticosteroids provide no benefit for bronchiolitis and increase adverse effects. Nebulized hypertonic saline (3%) shows modest benefit in reducing length of stay for admitted patients (though evidence is conflicting) but is not beneficial in the ED setting. Antibiotics have no role unless a documented secondary bacterial infection exists. Chest physiotherapy provides no benefit and may worsen respiratory distress. Nebulized epinephrine may provide transient improvement but shows no sustained benefit and is not recommended as routine therapy.

<image>Summary infographic of evidence-based bronchiolitis management showing interventions categorized as recommended (nasal suctioning, supplemental oxygen, IV/NG hydration), conditionally recommended (HFNC, hypertonic saline for inpatients), and not recommended (albuterol, corticosteroids, antibiotics, chest physiotherapy, routine CXR)</image>

Disposition and Discharge Criteria

Admission is indicated for respiratory rate greater than 70, SpO2 below 90% on room air, significant apnea, inability to feed, toxic appearance, or age under 4-6 weeks. Discharge criteria include SpO2 of 90% or greater on room air for at least 4 hours (including sleep), adequate oral intake (50% or more of baseline), manageable work of breathing, and family ability to perform nasal suctioning and recognize worsening. The safe-to-discharge SpO2 threshold remains debated, with the AAP using 90% while some institutions use 92%.

RSV Prevention

Nirsevimab (Beyfortus)

Nirsevimab is a long-acting monoclonal antibody against the RSV F protein administered as a single IM injection providing approximately 5 months of protection. The CDC recommended it in 2023 for all infants under 8 months entering their first RSV season, with additional recommendation for children 8-19 months at increased risk entering their second season. Efficacy shows approximately 75-80% reduction in RSV-associated hospitalizations based on the MELODY and HARMONIE trials. It largely replaces palivizumab for most indications.

Palivizumab (Synagis)

Palivizumab requires monthly IM injections for 5 months during RSV season and has been largely supplanted by nirsevimab. It may still be used when nirsevimab is unavailable. AAP criteria target primarily infants born before 29 weeks, those with hemodynamically significant CHD, and those with chronic lung disease of prematurity.

Maternal RSV Vaccine (Abrysvo)

The RSVpreF vaccine is administered during pregnancy at 32-36 weeks gestation, providing passive antibody transfer that protects newborns during the first 6 months. It serves as an alternative to infant nirsevimab (one or the other is recommended, not both).

<image>RSV prevention strategy flowchart comparing nirsevimab (single dose for all infants, broad population coverage), palivizumab (monthly dosing for high-risk infants), and maternal RSV vaccination (gestational weeks 32-36), with efficacy data and current recommendations for each approach</image>

Clinical Pearls

Bronchiolitis is a clinical diagnosis, and ordering a chest X-ray typically leads to unnecessary antibiotics rather than helpful information. The most important interventions are suctioning, hydration, and oxygen; everything else is unproven. Apnea may be the presenting sign of RSV bronchiolitis in young infants, especially former preterm infants, requiring careful monitoring. Albuterol should not be started "just to try it" without a clear plan to objectively assess response and discontinue if no improvement is observed. Infants with bronchiolitis who receive antibiotics are often given them because of an unnecessary chest X-ray showing atelectasis mistaken for pneumonia. Post-bronchiolitis wheezing is common and does not necessarily indicate asthma; recurrent viral-triggered wheezing may resolve by age 3-5.

Key Controversy: Nirsevimab for All Infants vs. High-Risk Only

The universal nirsevimab recommendation represents a paradigm shift from high-risk-only prevention (palivizumab) to population-level prevention. Supply constraints during the 2023-2024 season led to prioritization frameworks. Cost considerations (approximately $500 per dose for a common self-limited illness) raise questions about cost-effectiveness depending on hospitalization rates. Equity concerns center on ensuring access in under-resourced communities that bear the greatest burden of severe RSV disease. Some argue resources would be better spent on targeted high-risk prophylaxis and parental education. The long-term population impact on RSV epidemiology and potential age-shift of disease remains unknown.

References

• Ralston SL, et al. Clinical Practice Guideline: The Diagnosis, Management, and Prevention of Bronchiolitis (AAP). Pediatrics. 2014;134(5):e1474-e1502.
• Florin TA, et al. Biomarkers and Disease Severity in Children with Community-Acquired Pneumonia. Pediatrics. 2020;145(6):e20193728.
• Hammitt LL, et al. Nirsevimab for Prevention of RSV in Healthy Late-Preterm and Term Infants (MELODY Trial). N Engl J Med. 2022;386(9):837-846.
• Franklin D, et al. A Randomized Trial of High-Flow Oxygen Therapy in Infants with Bronchiolitis. N Engl J Med. 2018;378(12):1121-1131.
• Schuh S, et al. Effect of Nebulized Hypertonic Saline in Infants Hospitalized with Bronchiolitis. JAMA Pediatr. 2014;168(7):657-663.
• Kampmann B, et al. Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants (Abrysvo). N Engl J Med. 2023;388(16):1451-1464.

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