Classification of Bronchiolar Disorders




  • General Comments
    • Peak Age Groups
      • Common in infants and children: typically occurs in children <2 y/o
      • Rare in adults
  • Adenovirus (see Adenovirus, [[Adenovirus]])
  • Human Metapneumovirus (see Metapneumovirus, [[Metapneumovirus]])
  • Influenza A/B Virus (see Influenza Virus, [[Influenza Virus]])
  • Measles Virus (see Measles Virus, [[Measles Virus]])
  • Mycoplasma (see Mycoplasma Pneumoniae, [[Mycoplasma Pneumoniae]])
  • Legionellosis (see Legionellosis, [[Legionellosis]])
  • Parainfluenza Virus (see Parainfluenza Virus, [[Parainfluenza Virus]])
  • Respiratory Syncytial Virus (RSV) (see Respiratory Syncytial Virus, [[Respiratory Syncytial Virus]]): most cases with a defined viral etiology are due to RSV (RSV accounts for 45-90% of bronchiolitis cases in infants/young children)
  • Rhinovirus (see Rhinovirus, [[Rhinovirus]])

Toxic Fume Exposure

  • Ammonia Inhalation (see Ammonia, [[Ammonia]])
  • Chlorine Inhalation (see Chlorine, [[Chlorine]])
  • Nitrogen Dioxide Inhalation (see Nitrogen Dioxide, [[Nitrogen Dioxide]])
  • Nitrous Fumes (see Nitrous Fumes, [[Nitrous Fumes]]): found in silo gas, jet and missile fuels, metal pickling fumes, fires
  • Ozone Inhalation (see Ozone, [[Ozone]]) (low solubility in water): delayed injury to lower airways (bronchioles/alveoli)
  • Sulfur Dioxide Inhalation (see Sulfur Dioxide, [[Sulfur Dioxide]])
  • Phosgene Gas Inhalation (see Phosgene Gas, [[Phosgene Gas]])


  • Inflammatory Bowel Disease (see Inflammatory Bowel Disease, [[Inflammatory Bowel Disease]]): small case series have reported association with inflammatory bowel disease
  • Idiopathic Bronchiolitis: no clear history of exposure or infection


Infectious Bronchiolitis

  • Acute Inflammatory Disorder of Small Airways: peribronchiolar inflammation with epithelial cell necrosis
    • Air Trapping/Hyperinflation
    • Atelectasis

Toxic Fume Bronchiolitis

  • Determinants of Potential for Damage
    • Particle Size
      • Particles >10 µm will impact in upper airway
      • Particles <5 µm will impact in the lower airways and alveoli
    • pH: acid burns coagulate underlying tissue but alkali (ammonia, etc.) liquefact and penetrate mucosa
    • Chemical Reactivity
    • Water Solubility


  • Arterial Blood Gas (ABG)
    • Hypoxemia: may persist for weeks after recovery
  • CBC: absence of leukocytosis (and normal differential)
  • CXR/Chest CT Patterns
    • Hyperinflation with Air Trapping
    • Flattened Diaphragms
    • Peribrobchial Thickening
    • Focal Atelectasis
    • Pneumonia
    • Nodular Shadows: may be seen in some cases of infectious bronchiolitis
  • Pulmonary Function Tests (PFT’s): small airways (<2 mm) pattern
    • FEF25-75: decreased
    • Increased airway resistance and peripheral airway obstruction (and hypoxemia) may be seen years later in children who have experienced repeated episodes of RSV bronchiolitis
  • Bronchoscopy : usually not specifically helpful but may reveal organisms in infectious cases
  • Lung Biopsy: may be necessary in chronic progressive cases

Clinical Presentations

Infectious Bronchiolitis

General Comments

  • Risk of Hospitalization and Severe Bronchiolitis: high in infants with congenital heart disease, immunodeficiency, prematurity, or chronic lung disease
  • Risk of Severe Bronchiolitis: high in infants with family history of asthma and second-hand smoke exposure
  • Prodrome: several days of upper respiratory tract symptoms

Pulmonary Manifestations

  • Absence of Fever
  • Atelectasis (see Atelectasis, [[Atelectasis]])
  • Hyperinflation
  • Hyperresonant Chest Exam
  • Inspiratory Crackles on Chest Exam
  • Inspiratory/Expiratory Wheezing (see Obstructive Lung Disease, [[Obstructive Lung Disease]])
  • Intercostal/Suprasternal Retractions
  • Nasal Flaring
  • Tachypnea (see Tachypnea, [[Tachypnea]])

Toxic Fume Bronchiolitis

Mild Exposure Pattern

  • May be Asymptomatic
  • Bronchiolitis Obliterans (see Bronchiolitis Obliterans, [[Bronchiolitis Obliterans]]): variably occurs 2-8 wks after exposure
    • Gradual Onset of Dyspnea (see Dyspnea, [[Dyspnea]])
    • Dry Cough (see Cough, [[Cough]])

Moderate Exposure Pattern

  • Bronchiolitis (occurs hours-up to weeks after exposure)
  • Recovery: over days-wks after exposure
  • Bronchiolitis Obliterans (see Bronchiolitis Obliterans, [[Bronchiolitis Obliterans]]): occurs 2-8 weeks after exposure

Severe Exposure Pattern

  • Acute Lung Injury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]]): occurs 3-30 hrs after exposure
    • Pathology: diffuse alveolar damage
  • Recovery: over days-wks
  • Bronchiolitis Obliterans (see Bronchiolitis Obliterans, [[Bronchiolitis Obliterans]]): occurs 2-8 weeks after exposure


Infectious Bronchiolitis

Natural Course

  • Usually self-limited: recovery occurs within days-weeks

Infection Control/Contact Precautions

  • Crucial to prevent nosocomial spread of RSV (especially in immunocompromised populations)

Oxygen (see Oxygen, [[Oxygen]])

  • As required to treat hypoxemia


  • Crucial, as tachypnea can be dehydrating in infants -> important to avoid complication of hyponatremia


  • Only indicated if secondary bacterial infection is present

Bronchodilators (see Albuterol, [[Albuterol]])

  • Meta-Analysis of Bronchodilator Use in Bronchiolitis (2014) [MEDLINE]: bronchodilators (albuterol, salbutamol) do not improve hypoxemia, decrease rate of hospital admission after outpatient treatment, decrease the duration of hospitalization, or decrease the time to resolution of illness at home
    • However, study was limited by small sample sizes, lack of standardized study design, and lack of validated outcomes across the studies

Nebulized Racemic Epinephrine (see Epinephrine, [[Epinephrine]])

  • Infants: not efficacious [MEDLINE]

Corticosteroids (see Corticosteroids, [[Corticosteroids]])

  • Infants: not recommended
  • Adults: useful to specifically treat exacerbation of bronchospasm (asthma, COPD) triggered by RSV infection

Ribavirin (see Ribavirin, [[Ribavirin]])

  • Ribavirin is Highly Active Against RSV in vitro
  • Immunocompromised Adults with Stem Cell Transplant: aerosolized ribavirin decreases mortality rate in RSV pneumonia in this population [MEDLINE] [MEDLINE]
  • Immunocompromised Adults with Stem Cell Transplant: oral and intravenous ribavirin have been shown to be efficacious in small trials [MEDLINE] [MEDLINE]
  • Immunocompromised Adults with Lung/Solid Organ Transplant: the efficacy of ribavirin in these patients is unknown [MEDLINE] [MEDLINE]

Palivizumab (Synagis) (see Palivizumab, [[Palivizumab]]): RSV-specific humanized monoclonal antibody

  • No clinical benefit in the therapy of RSV infection
  • Licensed for the prevention of serious RSV lower respiratory tract disease in children at high risk of RSV infection (prematurity, bronchopulmonary dysplasia, congenital heart disease)

Combination Ribavirin + Intravenous Immunoglobulin (IVIG) (see Ribavirin, [[Ribavirin]] and Intravenous Immunoglobulin, [[Intravenous Immunoglobulin]])

  • May be indicated in severely ill patients with RSV

Combination Palivizumab (Synagis) + Intravenous Immunoglobulin (IVIG) (see Palivizumab, [[Palivizumab]] and Intravenous Immunoglobulin, [[Intravenous Immunoglobulin]]): has not been studied

RSV-Specific Immunoglobulin (RSVIG)

  • No longer available

Combination Ribavirin + Corticosteroids (see Ribavirin, [[Ribavirin]] and Corticosteroids, [[Corticosteroids]])

  • Has been used in small series of lung transplant patients with RSV [MEDLINE]

Toxic Fume Exposure

  • Supportive care


  • Mild Cases: resolve within several days
  • Mortality Rates
    • Previously Healthy Infants: 0.5-1.5%
    • Infants with Immunodeficiency/Cancer Chemotherapy/Pulmonary or Heart Disease/Pulmonary Hypertension: 15-40%


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