Bronchiolitis is a lower respiratory tract infection (LRTI) characterized by inflammation of the bronchioles in children < 2 years of age. Respiratory syncytial virus (RSV) is the primary pathogen, although many viruses have been implicated in bronchiolitis. Patients first present with upper respiratory tract infection (URTI) symptoms (e.g., low-grade fever, nasal congestion) followed by a cough, wheezing, and, in severe cases, signs of acute respiratory distress. Bronchiolitis is a clinical diagnosis; diagnostic studies are usually not needed unless the child presents with severe illness that requires an evaluation for associated complications (e.g., superinfection, respiratory acidosis) or if the diagnosis is uncertain. Management consists of supportive treatment (e.g., nasal suction) and close monitoring. Severe illness requires hospitalization for additional management (e.g., IV fluids, respiratory support, nutritional support) and close monitoring of respiratory status.
- Primarily affects children < 2 years of age
- Peak incidence: 2–6 months of age
- Common during winter months
Epidemiological data refers to the US, unless otherwise specified.
- Most common: respiratory syncytial virus (RSV)
- Less common
Risk factors for severe bronchiolitis 
- Age < 12 weeks
- Preterm birth (< 34 weeks' gestational age)
- Congenital heart or lung disease
- Neurological disease
- Exposure to tobacco smoke 
- Initially, URTI symptoms (e.g., copious rhinorrhea, low-grade fever, cough) 
- Followed by LRTI symptoms 
- Crackles, wheezes; , and/or rhonchi on auscultation 
- Findings vary minute-to-minute as mucus is cleared and/or respiratory efforts change.
- Severe illness: respiratory distress (usually occurs in children < 1 year of age)
- Often associated with poor feeding 
If significant nasal congestion is present, provide nasal suction and reassess respiratory status to differentiate upper airway involvement (clear breath sounds after nasal suction) from lower airway involvement (abnormal breath sounds after nasal suction). 
Symptoms typically peak 3–5 days after onset and then gradually improve over 2–3 weeks. The onset of new symptoms or worsening of existing symptoms (e.g., fever) after 3–5 days should raise concern for complications of bronchiolitis. 
General principles 
- Bronchiolitis is a clinical diagnosis based on the patient's age (< 2 years) and the presence of classic clinical features of bronchiolitis.
Further testing is not usually required but may be considered in patients with:
- Severe disease, e.g., if there is concern for respiratory failure
- Suspected complications of bronchiolitis
- Diagnostic uncertainty to rule out differential diagnoses of bronchiolitis
Laboratory studies 
Blood gas 
- Indicated for worsening severe disease and/or impending respiratory failure
- May show hypoxemia and/or CO2 retention
Respiratory viral panel
- Hospitalized infants receiving palivizumab prophylaxis
- Consider if patient cohorting is planned.
- Findings 
- 60–75% are positive for RSV
- Coinfections are present in up to one-third of those tested
Studies to exclude differential diagnoses (not routinely recommended)
- Blood culture
- Urinalysis and urine culture 
- CBC and BMP
- Indications: severe disease if there is diagnostic uncertainty or suspected complications (e.g., pneumothorax, pneumonia)
- Nonspecific findings, e.g., peribronchial thickening, hyperinflation of the lungs, interstitial infiltrates, atelectasis
- Superimposed complications, e.g., pneumonia
- Determine the need for immediate respiratory support.
- Hypoxemia (i.e., O2 ≤ 90% on room air): oxygen therapy via nasal cannula
- Refractory hypoxemia, signs of respiratory distress, respiratory failure: intubation, CPAP, or high-flow nasal cannula
- Start supportive measures including adequate hydration, relief of nasal congestion and/or obstruction, and monitoring.
- Screen for admission criteria for bronchiolitis and initiate inpatient management of bronchiolitis if present.
- Provide outpatient management of bronchiolitis with close medical follow-up for patients who do not meet the admission criteria.
Children with bronchiolitis and oxygen saturation ≥ 90% do not require supplemental oxygen. 
Avoid bronchodilators, epinephrine, corticosteroids, antibiotics, and chest physiotherapy unless there are comorbidities (e.g., asthma, croup, cystic fibrosis, acute otitis media). 
Admission criteria for bronchiolitis 
- Unwell appearance, lethargy
- Moderate to severe signs of respiratory distress (including significantly elevated respiratory rate for age)
- Ongoing respiratory support required
- Need for supplemental hydration
- History of apnea
- Consider if:
- Risk factors for severe bronchiolitis are present
- Supportive care at home is not feasible 
Inpatient management of bronchiolitis 
- Frequently monitor routine vital signs including O2 saturation; consider using:
- Continuous pulse oximetry 
- An objective respiratory score 
- Adjust short-term oxygen therapy as needed.
- Provide regular external nasal suction. 
- Consider scheduled nebulizations with 3% hypertonic saline 
Hypertonic saline nebulizations may trigger bronchospasm. Discontinue treatment if nebulizations cause severe coughing fits and/or worsen the patient's respiratory status. 
Caloric and fluid support
- Ensure patients receive the recommended daily intake for their age.
- Encourage normal oral feeds (e.g., with breastmilk, formula, regular diet for age) as tolerated.
- Consider NG/IV fluids for any of the following: 
- Poor oral intake
- Respiratory rate consistently > 60–70 bpm
- Worsening respiratory status during feeds
- Symptoms of aspiration
Respiratory distress increases caloric and fluid requirements but also increases the risk for aspiration during oral feeds. Nutritional and fluid support via a feeding tube (orogastric or nasogastric) and/or intravenously is often necessary. 
- Start isolation precautions in accordance with local protocols (e.g., contact precautions for RSV). 
- If used, discontinue palivizumab prophylaxis. 
Outpatient management of bronchiolitis 
- Arrange follow-up within 24 hours. 
- Educate caregivers on:
- Signs of deterioration and the need to seek immediate medical attention if present 
- How and when to provide nasal suction
- The expected course of disease
- Encourage adequate oral caloric and fluid intake.
- Advise caregivers to avoid exposing the patient to second-hand smoke; offer counseling on smoking cessation for household members.
Advise caregivers to seek immediate medical attention if the child shows signs of deterioration such as dehydration, poor feeding, lethargy or irritation, new fever, and/or signs of respiratory distress. 
- No URTI symptoms
- Congenital heart disease
- Foreign body aspiration
- Congenital airway abnormalities (e.g., vascular ring)
- Congestive heart failure secondary to congenital heart disease 
- Monophonic: foreign body aspiration
- See also “Wheezing in children”.
- Asymmetric crackles: bacterial or viral pneumonia
- See also “Differential diagnosis of acute cough” and “Bronchitis.”
- Neonatal fever: neonatal sepsis
The differential diagnoses listed here are not exhaustive.
- Respiratory failure
- Otitis media
We list the most important complications. The selection is not exhaustive.
General measures 
- Educate caregivers on respiratory hygiene and hand hygiene.
- Encourage exclusive breastfeeding for the first 6 months of life.
- Advise avoiding large crowds.
- Inform caregivers about the increased risk of infection at daycare.
- Offer advice on smoking cessation to any individuals who smoke in the household to reduce tobacco smoke exposure.
Palivizumab prophylaxis 
- Palivizumab is a short-acting monoclonal antibody against RSV F protein.
- Provides passive immunization to RSV infection (paramyxovirus)
- Reduces bronchiolitis hospitalizations in infants at risk for severe bronchiolitis
Indications in infants < 12 months of age 
- Preterm birth at < 29 weeks' gestational age 
- Chronic lung disease of prematurity
- Hemodynamically significant congenital heart disease
- Consider for selected patients with anatomical or neuromuscular conditions that impair mucous clearance.
Consider in certain patients < 24 months of age 
- Those with chronic lung disease of prematurity with a recent need for oxygen or pharmacotherapy
- Severely immunocompromised patients
- Selected patients with cystic fibrosis 
- Monthly IM palivizumab during RSV season 
- If the child is hospitalized with RSV infection, discontinue for the remainder of the RSV season. 
Palivizumab is used for RSV (Paramyxovirus) Prophylaxis in infants who are Premature or have Preexisting conditions (e.g., chronic lung disease of prematurity, congenital heart disease, immunocompromise).
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