Acute Bronchiolitis

Overview

Definition

Acute bronchiolitis is a clinical constellation of respiratory symptoms (increased work of breathing, wheezing, and crackles) caused by acute inflammation of the small airways (small bronchi and bronchioles), typically secondary to viral infections.

Epidemiology

• Population statistics:
  • Peak incidence between 2 and 6 months of age
  • Leading cause of hospitalization of infants in the United States
• Seasonal preference (respiratory syncytial virus (RSV)–related): fall and winter 
• Risk factors for severe disease:
  • Individual factors:
    • Prematurity (born < 37 weeks of gestation)
    • < 12 weeks of age
    • Low birth weight (< 2.5 kg)
    • Immunodeficiency
    • Congenital heart disease
    • Cystic fibrosis
    • Bronchopulmonary dysplasia (BPD)
  • Environmental factors:
    • Overcrowding (daycare or household)
    • Passive smoke inhalation
    • Contact with school-age siblings
    • Low socioeconomic status
    • Not breastfed

Etiology

• Viral infection:
  • RSV: ⅓ of cases
  • Rhinovirus
  • Less common: 
    • Parainfluenza virus
    • Human metapneumovirus
    • Influenza virus
    • Adenovirus
    • Mycoplasma pneumoniae 
    • Pertussis

Pathophysiology and Clinical Presentation

Pathophysiology

Pathological changes are noted within 24 hours of contact with a pathogen:

• Virus enters epithelial cells of terminal bronchioles.
• Inoculation causes inflammation → edema, mucus secretion, and epithelium sloughing
• Sloughing and edema → narrowing and obstruction of small airways
• Narrowing results in atelectasis and symptoms begin to appear.

Clinical presentation

Symptoms are on a spectrum based on the severity of the disease:

• Initial 1–3 days (upper respiratory tract symptoms):
  • Cough
  • Congestion
  • Rhinorrhea
• Peaks on day 3–5, lasting up to 10 days (lower respiratory tract symptoms):
  • Wheezing and diffuse crackles on lung exam
  • Fever
  • Shortness of breath
• Severe cases:
  • Apnea in infants, especially during sleep
  • Respiratory failure:
    • Tachypnea
    • Cyanosis
    • Nasal flaring
    • Grunting
    • Intercostal retraction
    • Hypoxia < 92% saturation

Diagnosis and Management

Diagnosis

• Diagnosis based on clinical suspicion: 
  • Characteristic lower respiratory tract symptoms
  • Patients < 2 years
  • Presenting during the fall and winter seasons
• Further investigation: 
  • High fever
  • Severe presentation 
  • History of comorbidities
• Routing testing of any kind is discouraged as it adds no additional therapeutic value.
• Investigation in severe cases to evaluate comorbid conditions or superimposed infection:
  • Complete blood count (CBC): leukocytosis 
  • Chest X-ray: hyperinflation with atelectasis 
  • RSV testing on aspirate

Management

Management depends on severity:

• Mild-to-moderate cases → supportive:
  • Caregiver education on upright positioning during sleeping and feeds
  • Use of cool-mist humidifier and antipyretic
  • Bulb suctioning of oral and nasal secretions
  • Maintain hydration and feeding
  • Follow-up if patient worsens
• Severe (< 28 days old, apnea, respiratory distress, lethargic):
  • Admit for inpatient care
  • Humidified oxygen and nebulized hypertonic saline
  • Suctioning of secretions
  • IV hydration
  • No evidence to support use of albuterol, epinephrine, or corticosteroids
• Complications, such as pneumonia and respiratory failure, can occur and must be managed accordingly.

Prevention and Prognosis

Prevention

• Encourage breastfeeding.
• Stop exposure to second-hand smoke.
• Hand hygiene 
• Palivizumab (monoclonal antibody) in high-risk patients: 
  • Meeting American Academy of Pediatrics (AAP) criteria for neonatal chronic lung disease:
    • Born at < 32 weeks gestation 
    • Requiring supplemental oxygen during the first 28 days of life
  • > 1 year old at onset of RSV season OR >2 years old but requiring medication for neonatal chronic lung disease

Prognosis

• Bronchiolitis is self-limiting, lasting 7–10 days.
• Only 3% of patients require hospitalization, and recover completely within 28 days.

Differential Diagnosis

• Asthma: an inflammatory airway disease that leads to bronchial luminal narrowing and thus obstruction of airflow. Characterized by cough, wheezes, and dyspnea. Asthma is usually diagnosed after the age of 2 and has known triggers, with reversibility of symptoms with bronchodilator use in all cases, differentiating this condition from bronchiolitis.
• Pneumonia: infection of the lower respiratory tract that results in symptoms very similar to bronchiolitis in infants. Patients with bronchiolitis may develop atypical pneumonia due to superimposed bacterial infections or worsened viral infections. Chest X-ray findings typically lag behind presentation in these cases, so the diagnosis is made when a patient has sustained hypoxia with increased oxygen supplementation, consolidations on lung exam, and increased work of breathing.
• Gastroesophageal reflux disease (GERD): Acid reflux into the esophagus in infancy and childhood may present with intermittent cough and wheezing. May also be accompanied by a lack of weight gain and increased irritability. Gastroesophageal reflux disease can be differentiated from bronchiolitis if symptoms correlate to feeding routine and not seasonality. Bronchiolitis usually presents with a history of upper respiratory symptoms prior to wheezing.