Acute Bronchiolitis

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | Referral

Definition

Acute bronchiolitis is a viral lower respiratory tract infection that primarily affects infants and young children. It causes inflammation and obstruction of the small airways (bronchioles), leading to respiratory distress.

Aetiology

The most common cause is Respiratory Syncytial Virus (RSV). Other viral causes include:

  • Rhinovirus.
  • Parainfluenza virus.
  • Human metapneumovirus.
  • Adenovirus.
  • Influenza virus.

Pathophysiology

Bronchiolitis is caused by viral infection leading to:

  • Inflammation and oedema of the bronchioles.
  • Increased mucus production, leading to airway obstruction.
  • Air trapping and atelectasis (lung collapse).
  • There is an imbalance between the lung ventilation (air flow) and lung perfusion (blood flow) or V/Q mismatch, resulting in hypoxia.

Risk factors

  • Age <12 months (peak incidence at 3–6 months).
  • Prematurity (<37 weeks gestation).
  • Congenital heart disease.
  • Chronic lung disease (e.g., bronchopulmonary dysplasia).
  • Immunodeficiency.
  • Exposure to cigarette smoke.
  • Nursery or daycare attendance.

Signs and symptoms

Symptoms:

  • Prodromal upper respiratory symptoms (nasal congestion, cough, low-grade fever).
  • Progressive respiratory distress.
  • Poor feeding and lethargy in severe cases.

Signs:

  • Tachypnoea (rapid breathing).
  • Wheezing and fine inspiratory crackles.
  • Subcostal/intercostal recessions (indicating increased effort to breathe).
  • Nasal flaring and grunting (signs of severe distress).
  • Cyanosis in severe cases.

Investigations

Bronchiolitis is a clinical diagnosis in most cases. Investigations may be needed in severe or atypical cases:

  • Pulse oximetry: essential to assess oxygen saturation.
  • Nasal swab PCR: can confirm viral aetiology but rarely alters management.
  • Chest X-ray: only indicated if severe illness or suspected pneumonia; may show hyperinflation or peribronchial thickening.
  • Blood gas analysis: if respiratory distress is severe, may show respiratory acidosis.

Management

1. Supportive Care:

  • Oxygen therapy: if SpO₂ <92%.
  • Fluids: NG tube or IV fluids if feeding is compromised.
  • Minimal handling: to reduce distress and work of breathing.

2. Pharmacological Management:

  • Salbutamol, corticosteroids, and antibiotics are NOT routinely recommended as they do not improve outcomes.
  • Consider nebulised hypertonic saline in hospitalised cases.

3. Respiratory Support (if needed):

  • High-flow nasal cannula (HFNC) oxygen: if moderate respiratory distress.
  • CPAP or mechanical ventilation: if severe respiratory failure.

Referral

Refer to secondary care if any of the following are present:

  • Severe respiratory distress: increased work of breathing, marked recessions.
  • SpO₂ persistently <92% despite oxygen.
  • Apnoea or cyanosis.
  • Poor feeding with dehydration.
  • High-risk infants: prematurity, underlying lung/heart disease.
 
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