Bronchiolitis
A viral infection of the smallest airways in infants that causes widespread small-airway obstruction and feeding difficulty; management is supportive because the pathology is mechanical mucosal swelling, not something a drug reverses.
In a nutshell
RSV inflames the bronchioles of an infant whose airways are already about a millimetre wide, so mucosal oedema and sloughed debris (not bronchospasm) obstruct them. Air trapping follows, and a baby too breathless to feed. There is nothing to reverse pharmacologically, so care is supportive.
Classic presentation
An infant under one year, in winter, with a few days of coryza followed by cough, tachypnoea, widespread wheeze and fine crackles, now feeding poorly.
Key points
- The obstruction is mucosal swelling and debris inside a tiny airway. A small amount of swelling collapses airflow, so the infant's airway calibre is the whole disease.
- Partially obstructed bronchioles act as one-way valves: air enters on inspiration and is trapped on expiration. Hence hyperinflation, widespread wheeze and fine inspiratory crackles.
- Feeding is the clinical readout. An infant cannot suck and breathe hard at the same time, so intake measures respiratory effort better than any single number.
- Bronchodilators, corticosteroids and antibiotics do not change the course: infant bronchioles have little smooth muscle to relax, and this is not a bacterial infection.
- Apnoea is a recognised presentation, particularly in young or ex-premature infants, and may come before obvious respiratory distress.
- It is a clinical diagnosis. Pulse oximetry guides oxygen and admission; viral testing is for cohorting, not for treatment decisions.
First-line investigation
None routinely: the diagnosis is clinical. Pulse oximetry detects the hypoxia from ventilation-perfusion mismatch and guides oxygen and admission.
First-line management
Supportive care: minimal handling, nasal suction if secretions block feeding, oxygen for hypoxia, and nasogastric or intravenous fluids if the infant cannot feed.
Exam traps
- Salbutamol is the wrong answer. Wheeze in an infant with bronchiolitis is not bronchospasm.
- A tiring infant's respiratory rate falls before they decompensate. A settling rate with worsening effort is deterioration, not improvement.
- Apnoea can be the presenting feature in a young or ex-premature infant, with little else to find on examination.
Educational content pending clinical review. Not medical advice.