Bronchiolitis

Inflammation of the small airways (bronchioles) causing airflow obstruction. In infants it typically manifests as an acute viral infection (most often RSV), whereas in adults it often refers to a chronic fibrotic bronchiolitis (obliterans) with irreversible lung injury.

• Bronchiolitis is extremely common in infancy – a leading cause of hospitalization for babies and responsible for significant infant morbidity and mortality worldwide. It's a must-know for pediatrics and exams. Adult forms (e.g. post-transplant bronchiolitis obliterans) cause serious, often irreversible, small-airway damage that physicians should recognize in the proper context.

• Infants: Typically a <1-year-old with a viral URI (runny nose, congestion) for 2–3 days that progresses to cough, wheezing, and difficulty feeding. Exam shows tachypnea, diffuse wheezes and crackles, and signs of respiratory distress (intercostal retractions, nasal flaring).
• Severe infant bronchiolitis: May present with hypoxemia (O₂ sat <90%), cyanosis, or episodes of apnea (especially in young infants). Risk factors for severe disease include prematurity, age <3 months, and underlying cardiopulmonary or immunologic conditions, which lower the threshold for hospital admission.
• Adults: Bronchiolar inflammation usually presents as a progressive dyspnea on exertion with chronic cough rather than an acute illness. For example, lung transplant recipients may develop bronchiolitis obliterans syndrome (chronic rejection) manifesting as gradually declining FEV₁ and exercise tolerance a few years post-transplant. On exam, inspiratory crackles or wheezing might be heard; expiratory high-resolution CT often shows a patchy mosaic pattern from air-trapping.

1. Clinical diagnosis (infants): Suspect bronchiolitis in an infant with first-time wheezing during peak viral season. Specific viral testing (e.g. RSV PCR) is optional in typical cases, but may be done in hospitalized infants for cohorting or if results would change management (e.g. identifying influenza for antivirals).
2. Assess severity: Evaluate hydration status (feeding volume, wet diapers) and work of breathing. Check oxygen saturation (give O₂ if <92%). Chest X-ray is not routinely needed unless atypical features (e.g. focal findings or severe course) suggest pneumonia or other diagnosis; when obtained, X-ray may show lung hyperinflation with patchy atelectasis.
3. Admission criteria: Infants with persistent O₂ sat <90% on room air, respiratory rate >70/min, or signs of significant distress (grunting, severe retractions, apnea, dehydration) should be hospitalized for supportive care. Young age (<3 months) or high-risk comorbidities also lower the threshold for admit.
4. Adult evaluation: In adults with suspected bronchiolitis obliterans, obtain spirometry (often shows an irreversible obstructive pattern) and HRCT with expiratory cuts (to identify mosaic air-trapping). A lung biopsy can provide a definitive diagnosis, though transbronchial biopsy often misses the patchy lesions; sometimes a surgical lung biopsy is needed if diagnosis is unclear.
5. Rule out other causes: In infants, consider foreign body aspiration (sudden onset localized wheezing or asymmetric breath sounds), or bacterial pneumonia (high fever, focal crackles or consolidation on imaging) if presentation is atypical. In older children with recurrent wheezing, asthma becomes more likely (history of atopy, improvement with bronchodilators).

1. Supportive care is the mainstay for infant bronchiolitis. Ensure adequate hydration (IV or NG fluids if poor oral intake), use gentle nasal suctioning, and give supplemental oxygen to maintain sats ≥90%. High-flow nasal cannula oxygen can help avoid intubation in babies with severe respiratory distress.
2. No proven fast remedies – bronchodilators, nebulized epinephrine, and corticosteroids have shown no consistent benefit and are not recommended for routine use. Antibiotics should be given only if a concurrent bacterial infection is strongly suspected (e.g. acute otitis media or lobar pneumonia).
3. Antiviral therapy plays a limited role. If testing reveals influenza, treat with oseltamivir (especially if started within 48 hours). For other viruses (RSV, rhinovirus, etc.), no specific antivirals are available (management remains supportive).
4. Prevention: For RSV, immunoprophylaxis significantly reduces illness severity. A maternal RSV vaccine (given in late pregnancy) or the long-acting monoclonal antibody nirsevimab for newborns can prevent bronchiolitis in the first RSV season. High-risk infants (premature, chronic lung or heart disease) who did not receive those may still receive monthly palivizumab during RSV season.
5. In adults with bronchiolitis obliterans, treatment is challenging. Address the underlying cause: enhance immunosuppression for post-transplant rejection (e.g. optimize calcineurin inhibitors, consider high-dose steroids), treat inflammatory causes (e.g. corticosteroids for organizing pneumonia), or use macrolide antibiotics long-term for diffuse panbronchiolitis. Provide supportive therapy (inhalers, oxygen) and evaluate for lung transplantation in advanced cases.

• Unlike asthma, bronchiolitis usually does not significantly improve with bronchodilator therapy – guidelines advise against routine use of albuterol or steroids in infants.
• Palivizumab (monthly monoclonal antibody) was traditionally given to high-risk infants to prevent RSV bronchiolitis; now newer passive immunization (nirsevimab) or maternal RSV vaccination can protect most infants during RSV season.
• In infants <2 months, apnea can be an early warning sign of severe bronchiolitis (especially with RSV) – any apneic episode in a baby with a cold should prompt urgent evaluation.

• Apnea or episodes of breathing cessation (especially in young infants) – often a precursor to respiratory failure in bronchiolitis. Any apnea warrants hospitalization and possible ICU support.
• Signs of impending failure: sustained O₂ saturation <90% despite support, grunting respirations, severe chest indrawing, or lethargy (fatigue from breathing) are ominous and indicate need for escalated care (e.g. high-flow O₂, mechanical ventilation).

1. Infant with URI symptoms (rhinorrhea, cough) and new wheezing → suspect bronchiolitis (most commonly RSV).
2. Assess severity: check feeding/hydration, work of breathing (retractions, apnea), and O₂ sat.
3. If mild (feeding well, no or minimal dyspnea, O₂ sat normal) → outpatient management with nasal saline drops, suctioning, and frequent feeds; schedule follow-up and educate parents on warning signs.
4. If significant distress or risk factors (hypoxia, dehydration, apnea, age <3 mo, etc.) → hospitalize for supportive care: humidified oxygen, IV/NG fluids, frequent suction, and close monitoring.
5. In the hospital, continue supportive care and monitor. Do not give bronchodilators or steroids routinely (only consider a monitored trial if an asthma component is suspected). No antibiotics unless a bacterial co-infection is evident. Ensure appropriate follow-up and consider RSV prophylaxis measures after discharge for eligible infants.

• A 4‑month‑old infant in December has a few days of runny nose and cough, now with wheezing, difficulty feeding, and intercostal retractions. Oxygen saturation is 91%. The baby is likely suffering from acute bronchiolitis, most often caused by RSV.
• A double‑lung transplant recipient 5 years post-surgery gradually develops cough, dyspnea, and declining spirometry (↓FEV₁/FVC). Chest imaging shows hyperlucent areas from air-trapping. This presentation is classic for bronchiolitis obliterans syndrome (chronic rejection).