Lower Airway Disease
Bronchiolitis
Acute viral inflammation of the bronchioles causing airway edema, mucus production, air trapping, and variable small-airway obstruction.
Clinical vignette
An infant with cough, congestion, and increased work of breathing
A previously healthy 7-month-old presents on day four of illness with rhinorrhea, cough, decreased feeding, tachypnea, subcostal retractions, diffuse crackles, and expiratory wheezing. Oxygen saturation is 91% on room air. The infant is alert but has taken only half of the usual feeding volume.
What should you decide first?
Determine respiratory severity, hydration status, risk factors for deterioration, and whether supportive care can be provided safely at home.
Anatomy localization
The bronchioles
The disease localizes to the small, non-cartilaginous airways. Their narrow baseline diameter makes infants particularly vulnerable to obstruction from edema, mucus, and cellular debris.
Edema
Thickens the bronchiolar wall.
Mucus
Narrows and plugs the airway lumen.
Air trapping
Occurs when expiration is more limited than inspiration.
Pathophysiology
From viral infection to respiratory distress
Viral infection
A respiratory virus infects the bronchiolar epithelium.
Inflammation and epithelial injury
The infected airway develops epithelial injury, inflammation, and bronchiolar wall edema.
Mucus and cellular debris
Increased mucus production and sloughed epithelial cells further narrow the small-airway lumen.
Small-airway obstruction
Edema, mucus, and debris produce partial or complete bronchiolar obstruction.
Impaired ventilation
Air trapping, atelectasis, ventilation-perfusion mismatch, and increased work of breathing develop downstream.
Why does bronchiolitis wheeze if it is not asthma?
Wheezing is a sign of narrowed airways, not a diagnosis of bronchospasm. In bronchiolitis, small-airway obstruction is driven predominantly by bronchiolar edema, mucus, and cellular debris. These narrowed airways can generate expiratory wheezing even without the reversible smooth-muscle bronchoconstriction characteristic of asthma.
Clinical connection
Albuterol relaxes bronchial smooth muscle but does not directly remove mucus, cellular debris, or bronchiolar edema. This helps explain why bronchodilators are not routinely recommended for typical bronchiolitis.
History and physical exam
Assess severity, not just the diagnosis
History
- • Day of illness and trajectory
- • Feeding volume and urine output
- • Apnea, cyanosis, or fatigue
- • Prematurity or cardiopulmonary disease
- • Age, especially young infants
- • Prior wheezing or strong atopic history
Physical exam
- • Respiratory rate and work of breathing
- • Retractions, nasal flaring, or grunting
- • Crackles, wheezing, and air entry
- • Oxygen saturation and mental status
- • Hydration and perfusion
- • Focal findings suggesting an alternative diagnosis
Differential diagnosis
What else could look like this?
Asthma or viral-induced wheeze
Recurrent episodes, prior response to bronchodilator, atopy, or older age.
Pneumonia
Focal examination findings, persistent high fever, or toxic appearance.
Foreign body aspiration
Abrupt onset, asymmetric air entry, focal wheeze, or choking history.
Heart failure
Hepatomegaly, diaphoresis with feeds, poor growth, murmur, or cardiomegaly.
Pertussis
Paroxysmal cough, apnea, post-tussive emesis, or minimal fever.
Diagnostic workup
Typical bronchiolitis requires very little testing
Usually appropriate
- • Focused history
- • Repeated respiratory assessment
- • Hydration assessment
- • Pulse oximetry when clinically indicated
Avoid routinely
- • Chest radiograph
- • Respiratory viral panel
- • CBC or inflammatory markers
- • Albuterol
- • Nebulized epinephrine
- • Systemic corticosteroids
- • Antibiotics without suspected bacterial infection
- • Chest physiotherapy
Testing may be appropriate when the presentation is atypical, severe, prolonged, focal, or when another diagnosis would change management.
Management
Supportive care first
Nasal suctioning
Use gentle, targeted suctioning when secretions impair breathing or feeding.
Hydration
Continue oral feeds when safe; consider enteral or intravenous support when intake is inadequate.
Oxygen
Provide supplemental oxygen for persistent clinically significant hypoxemia according to local policy.
Respiratory support
Escalate support when work of breathing, oxygenation, apnea, or fatigue worsens.
Oxygen threshold note
Many bronchiolitis guidelines use a persistent oxygen saturation below approximately 90% as a threshold for supplemental oxygen, but institutional policies and patient comorbidities may differ.
Disposition
Admit the child, not the pulse oximeter
Consider admission
- • Persistent hypoxemia
- • Moderate or severe work of breathing
- • Apnea, exhaustion, or altered responsiveness
- • Inadequate feeding or dehydration
- • High-risk age or underlying disease
- • Unsafe home monitoring or limited follow-up
Reasonable discharge
- • Stable or improving respiratory effort
- • Adequate oxygenation on room air
- • Sufficient oral intake
- • Caregiver can perform basic nasal care
- • Clear return precautions
- • Appropriate follow-up access
Clinical pearls
High-yield takeaways
Bronchiolitis is a clinical diagnosis
Supportive care is the foundation of treatment
Use suctioning when it solves a problem
Do not investigate a classic presentation routinely
Wheezing does not automatically mean bronchodilators
Knowledge check
Test your bronchiolitis reasoning
Question 1
A comfortable 8-month-old with typical bronchiolitis has mild retractions, adequate feeding, diffuse wheezing and crackles, and an oxygen saturation of 95% on room air. What is the most appropriate next step?
Anki Deck
Bronchiolitis
Reinforce the highest-yield concepts from this module with 16 spaced-repetition cards.
Requires Anki. Deck content is intended for educational review and should be used alongside the full PediAtlas module.
Evidence Base
Clinical References
Diagnosis, management, and prevention of bronchiolitis.
Bronchiolitis: Recommendations for diagnosis, monitoring, and management.
Secondary Educational Sources
UpToDate and OpenEvidence were used for educational verification and consistency checks where appropriate.
Educational Disclaimer
PediAtlas is intended for medical education and should not replace institutional guidelines, local protocols, patient-specific assessment, or clinical judgment.