Bronchiolitis is an acute viral lower respiratory tract infection primarily affecting infants <2 years, most commonly caused by respiratory syncytial virus (RSV). It is the leading cause of infant hospitalization in high-income countries, with >100,000 hospitalizations annually in the US. [1-2] Management is supportive only — no pharmacologic therapy has been shown to shorten the disease course. [3-4]
1. History
- HPI essentials: Duration of URI prodrome (typically 2–4 days of rhinorrhea, congestion, low-grade fever before lower tract symptoms), cough character, feeding tolerance (volume and frequency), wet diapers/urine output, breathing difficulty, any apneic episodes [3][5]
- Timing: Peak severity occurs around day 3–5 of illness; symptoms typically resolve over 7–14 days, with 90% having cough resolution by 3 weeks [1]
- Seasonality: December–March in Northern Hemisphere; May–July in Southern Hemisphere [2]
- Important negatives: Absence of URI prodrome should raise suspicion for non-infectious causes (cardiac disease, congenital airway anomaly, foreign body) [1]
2. Alarm Features
- SpO₂ <90% (OR 8.9 for escalated care) [6]
- Nasal flaring/grunting (OR 3.8) [6]
- Apnea (OR 3.0) — especially in preterm infants and those <2 months [6]
- Retractions (intercostal, subcostal, supraclavicular) (OR 3.0) [6]
- Age ≤2 months (OR 2.1) [6]
- Dehydration/poor feeding (OR 1.9–2.1) [6]
- Cyanosis, lethargy, inability to maintain hydration
- Respiratory deterioration outside the expected natural history (consider bacterial superinfection) [1]
3. Medications
Not recommended (per AAP 2014 guideline)
- Albuterol/salbutamol — no improvement in SpO₂, admissions, or LOS; causes tachycardia, tremor, desaturation [4-5]
- Nebulized epinephrine — not recommended inpatient; may reduce ED admissions if given within 24 hours of presentation (NNT = 5), but no evidence for repeated use [5]
- Systemic/inhaled corticosteroids — no benefit on admissions or LOS [4-5]
- Antibiotics — only if concurrent bacterial infection suspected; macrolides do not shorten illness [4-5]
- Nebulized hypertonic saline — not recommended in the ED; may be considered inpatient (low-certainty evidence for modest LOS reduction of ~0.4 days) [4][7]
Supportive treatments
- Supplemental O₂ to maintain SpO₂ >90% [4-5]
- IV or NG fluids if unable to maintain oral hydration [8]
- Gentle nasal suctioning (avoid deep/aggressive suctioning) [5]
- Antipyretics as needed
4. Diet
- Feeding assessment is critical — poor feeding is a key marker of severity and dehydration risk [5]
- Small, frequent feeds are preferred; thickened feeds are not indicated
- If oral intake is inadequate, nasogastric feeding is preferred over IV fluids (similar outcomes, fewer complications) [8]
- Isotonic IV fluids if NG not feasible; monitor for SIADH in severe cases [1]
5. Review of Systems
- Respiratory: Cough, tachypnea, wheeze, noisy breathing, apnea
- GI: Feeding tolerance, vomiting, stool output (dehydration assessment)
- Neuro: Lethargy, irritability (may indicate hypoxia or severe disease)
- ENT: Rhinorrhea, congestion, ear pulling (otitis media complicates ~30% of cases)
- Constitutional: Fever (typically low-grade), activity level
- Extrapulmonary manifestations (rare, severe): Encephalitis, cardiomyopathy, hepatitis [1]
6. Collateral History and Family History
- Birth history: Gestational age, NICU stay, need for respiratory support
- Immunoprophylaxis status: Nirsevimab or palivizumab receipt, maternal RSV vaccination [9-10]
- Sick contacts/daycare exposure
- Household tobacco smoke exposure — independent risk factor for severity [1]
- Siblings <5 years in household — increases RSV acquisition risk [11]
- Breastfeeding history — breastfeeding <2 months is a risk factor for severe disease [1]
7. Risk Factors
- Age <12 weeks (strongest predictor of severe disease) [4][8]
- Prematurity (<37 weeks, especially <32 weeks) — accounts for ~25% of RSV hospitalizations [11]
- Congenital heart disease (hemodynamically significant) [11-12]
- Chronic lung disease/BPD [11]
- Immunodeficiency [4][8]
- Neuromuscular disease, Down syndrome [11-12]
- Tobacco smoke exposure [1]
- Low socioeconomic status, Indigenous ethnicity [1]
- Lack of breastfeeding, failure to thrive [1]
- Importantly, the majority of hospitalized infants are previously healthy term infants [8]
8. Differential Diagnosis
- Pneumonia — consider if consolidation, persistent focal rales, new fever, or deterioration outside expected course [1]
- Pertussis — paroxysmal cough, apnea, post-tussive emesis; consider in incompletely immunized infants [1][13]
- Reactive airway disease/asthma — recurrent wheezing, atopic history, response to bronchodilators [14]
- Foreign body aspiration — acute onset, unilateral wheeze, no URI prodrome [1]
- Congenital heart disease — persistent wheeze from birth, feeding difficulties, murmur, hepatomegaly [14]
- Congenital airway anomaly (vascular ring, tracheomalacia, bronchomalacia) — persistent stridor/wheeze from birth [14]
- Cystic fibrosis — recurrent respiratory infections, failure to thrive, steatorrhea [14]
- GERD — wheezing associated with feeds [14]
9. Past Medical History
- Prior wheezing episodes (bronchiolitis is defined as the first episode of wheezing in infants <12 months) [3]
- Prematurity and NICU course
- Congenital heart or lung disease
- Prior intubation or respiratory support
- Immunization status (pertussis vaccination)
- RSV immunoprophylaxis history
10. Physical Exam
- Vitals: Tachypnea (age-adjusted), tachycardia, SpO₂, temperature
- General: Level of alertness, hydration status (mucous membranes, fontanelle, skin turgor, capillary refill)
- Respiratory: Nasal flaring, grunting, intercostal/subcostal/supraclavicular retractions, prolonged expiratory phase [3][5]
- Auscultation: Diffuse wheezing, inspiratory crackles, coarse breath sounds; note that findings fluctuate minute-to-minute with mucus plugging/clearing [1]
- Assess for apnea — especially in preterm infants <2 months [3]
- Concerning findings: Silent chest, cyanosis, altered consciousness, poor respiratory effort (impending respiratory failure) [15]
11. Lab Studies
- Routine labs are NOT recommended per AAP guidelines — diagnosis is clinical [3-4]
- Viral testing (RSV rapid antigen or PCR/NAAT): May guide cohorting and infection control; not required for management [16]
- CBC, CRP: Not routinely indicated; may be considered if bacterial co-infection suspected (incidence <11%) [8]
- Blood gas: Only in impending respiratory failure
- Electrolytes: Consider if IV fluids initiated or concern for SIADH
- Blood culture/UA: Consider in febrile neonates <28 days per age-appropriate sepsis workup protocols
12. Imaging
- Chest radiography is NOT routinely recommended — increases unnecessary antibiotic use without changing outcomes [3-4]
- When to image: Atypical course, suspected pneumonia (focal findings, high/persistent fever), concern for foreign body, cardiac disease, or clinical deterioration
- Expected CXR findings (if obtained): Hyperinflation, peribronchial thickening, patchy atelectasis (often mistaken for infiltrate)
13. Special Tests
- No validated severity scoring tool exists with high predictive power for bronchiolitis [3][5]
- Escalated care risk score (Freire et al.): Uses SpO₂, nasal flaring/grunting, apnea, retractions, age, dehydration, poor feeding — AUC 85% for predicting need for HFNC/CPAP/ICU [6]
- Point-of-care ultrasound (POCUS): Emerging role for lung assessment; not yet standard
- Respiratory viral panel (multiplex PCR): Identifies co-infections (up to 30% of cases); useful for epidemiology and cohorting [16]
14. ECG
- Not routinely indicated in bronchiolitis
- Consider if suspecting cardiac disease as alternative diagnosis (murmur, hepatomegaly, persistent tachycardia disproportionate to respiratory distress)
- Severe bronchiolitis with myocarditis (rare) may show ST changes or arrhythmias
15. Assessment
- Clinical diagnosis based on history and physical exam: URI prodrome → lower respiratory symptoms (cough, tachypnea, wheeze/crackles, increased work of breathing) in an infant <24 months during viral season [3-4][17]
- Severity stratification:
- Mild: Feeding well, SpO₂ >92%, minimal/no retractions
- Moderate: Reduced feeding, SpO₂ 90–92%, moderate retractions
- Severe: Unable to feed, SpO₂ <90%, marked retractions, apnea, lethargy
- Peak illness at day 3–5; clinical fluctuation is expected and should not be confused with deterioration [1]
- Complications: Dehydration, apnea, respiratory failure, secondary bacterial infection (otitis media, pneumonia), SIADH
16. Treatment Plan
Initial stabilization (ED)
- Assess and stabilize airway, breathing, circulation
- Gentle nasal suctioning (bulb suction or low-pressure wall suction)
- Supplemental O₂ if SpO₂ ≤90% [4]
- Trial of feeding; if unable, initiate NG or IV fluids [8]
Escalation pathway
- High-flow nasal cannula (HFNC): Consider if persistent hypoxia or moderate-severe work of breathing despite standard O₂; may reduce need for ICU transfer (low-quality evidence) [5][18]
- CPAP: For worsening respiratory distress not responsive to HFNC [19]
- Intubation/mechanical ventilation: For respiratory failure, recurrent apnea unresponsive to CPAP
Do NOT administer: Albuterol, epinephrine, corticosteroids, antibiotics (unless bacterial co-infection), chest physiotherapy [4]
Minimal handling is recommended in moderate-severe cases to reduce energy expenditure [8]
17. Disposition
Admission criteria
- SpO₂ <90% on room air [5]
- Significant respiratory distress (nasal flaring, grunting, marked retractions) [5]
- Apnea [5]
- Inability to maintain oral hydration [5]
- Age ≤2 months with moderate symptoms [6]
- High-risk comorbidities (prematurity, CHD, CLD, immunodeficiency) with worsening symptoms [4]
ICU admission
- Need for HFNC >2 L/kg/min, CPAP, or mechanical ventilation
- Recurrent or prolonged apnea
- Impending respiratory failure
Discharge criteria
- SpO₂ >90% on room air for ≥4 hours (including sleep)
- Adequate oral intake (≥75% of baseline)
- Stable or improving respiratory status
- Caregivers able to perform nasal suctioning and recognize worsening signs
Specialist consultation triggers
- PICU for respiratory failure or recurrent apnea
- Cardiology if cardiac disease suspected
- Pulmonology for atypical course or recurrent episodes
18. Follow Up / Return Precautions
- Follow-up: Primary care within 24–48 hours of ED discharge; sooner if high-risk
- Return immediately for: Apnea/breathing pauses, worsening breathing difficulty, cyanosis/blue lips, refusal to feed or significantly decreased wet diapers, lethargy/difficult to arouse
- Counseling points:
- Illness typically worsens before improving; peak severity day 3–5 [1]
- Full recovery expected in 2–3 weeks; residual cough may persist
- Nasal suctioning before feeds and sleep
- Small, frequent feeds; upright positioning
- Hand hygiene and limiting exposure to sick contacts
- Prevention: Nirsevimab (single IM dose) is recommended by ACIP for all infants born during or entering their first RSV season (79% efficacy against medically attended RSV LRTI, 81% against hospitalization). Palivizumab (monthly IM) remains an option for high-risk infants entering their second RSV season if nirsevimab is unavailable. Maternal RSV vaccination (bivalent RSV prefusion F vaccine, 24–36 weeks gestation) provides passive protection through ~180 days of life. [5][9-10][20]
Images
References
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2. Parenteral Versus Enteral Fluid Therapy for Children Hospitalised With Bronchiolitis. — Gill PJ, Anwar MR, Kornelsen E, et al. The Cochrane Database of Systematic Reviews. 2021.
3. Viral Bronchiolitis in Children. — Meissner HC. The New England Journal of Medicine. 2016.
4. Clinical Practice Guideline: The Diagnosis, Management, and Prevention of Bronchiolitis. — Ralston SL, Lieberthal AS, Meissner HC, et al. Pediatrics. 2014.
5. Respiratory Syncytial Virus Bronchiolitis: Rapid Evidence Review. — Oppenlander KE, Chung AA, Clabaugh D. American Family Physician. 2023.
6. Predicting Escalated Care in Infants With Bronchiolitis. — Freire G, Kuppermann N, Zemek R, et al. Pediatrics. 2018.
7. Nebulised Hypertonic Saline Solution for Acute Bronchiolitis in Infants. — Zhang L, Mendoza-Sassi RA, Wainwright CE, Aregbesola A, Klassen TP. The Cochrane Database of Systematic Reviews. 2023.
8. Severe Respiratory Syncytial Virus Infection in Children: Burden, Management, and Emerging Therapies. — Mazur NI, Caballero MT, Nunes MC. Lancet. 2024.
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15. Preparation for Pediatric Emergencies in the Office: Technical Report. — Cantrell P, Hoffmann J, Yuknis M, et al. Pediatrics. 2026.
16. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). — Miller JM, Binnicker MJ, Campbell S, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2024.
17. Magnesium Sulphate for Treating Acute Bronchiolitis in Children Under Two Years of Age. — Chandelia S, Kumar D, Tandon D, Makol J. The Cochrane Database of Systematic Reviews. 2026.
18. High-Flow Nasal Cannula Therapy for Infants With Bronchiolitis. — Armarego M, Forde H, Wills K, Beggs SA. The Cochrane Database of Systematic Reviews. 2024.
19. Continuous Positive Airway Pressure (CPAP) for Acute Bronchiolitis in Children. — Jat KR, Dsouza JM, Mathew JL. The Cochrane Database of Systematic Reviews. 2022.
20. Nirsevimab and Hospitalization for RSV Bronchiolitis. — Assad Z, Romain AS, Aupiais C, et al. The New England Journal of Medicine. 2024.