Epidemiology

Bronchiolitis is a common presentation to emergency departments, with a seasonal pattern. It typically affects children under the age of 12 months, but may occur in children up to 2 years of age. The peak age is between 2 and 8 months of age, with males more commonly affected. Approximately 1% of children will require admission for bronchiolitis, which is the leading cause of admission for children with lower respiratory tract disease in the Western world.¹ Epidemics of bronchiolitis occur during each winter, with the peaking of respiratory viruses. While respiratory syncytial virus (RSV) is the commonest organism responsible for bronchiolitis, others include parainfluenza virus, adenovirus, rhinovirus and influenza. Bronchiolitis may also complicate exanthems such as measles and varicella in young children. It is estimated that by the age of 2, 70% of children have been exposed to RSV. Despite the frequency, mortality is low at less than 1% of hospitalised babies. High-risk patients include those with underlying chronic lung disease, congenital heart disease, neuromuscular disorders or corrected age less than 2 months of age.¹

Pathophysiology

Infection with RSV is associated with direct invasion of epithelial cells in the respiratory tract. Primary infection in young children and infants involves the lower respiratory tract. The bronchiolar epithelium is predominantly affected and an inflammatory response follows. Lymphocytes infiltrate the affected areas and oedema develops in the submucosa. Smooth muscle spasm ensues. The net result is that small airways become narrowed by the combination of oedema and muscle spasm, giving the typical clinical picture of bronchiolitis.

How this clinical picture emerges is still unclear. The role of pro-inflammatory regulators interleukin (IL)-6, IL-8, interferon-γ, and macrophage inflammatory protein-1β, as well as of the regulatory cytokine IL-10 in causing the disease as we know it, as opposed to facilitating healing and repair still remains to be elucidated.^2–4

The incidence of concomitant or secondary bacterial infection is low, although otitis media may occur. In the very young infant, apnoea may be the predominant symptom, with few other respiratory signs. Likewise, in neonates a non-specific sepsis-like picture with collapse may occur. In reinfection with RSV or primary infection in older children, the symptoms are more limited to the upper respiratory tract, causing signs consistent with a severe common cold.

History

Bronchiolitis typically presents with a prodrome of upper respiratory tract infection over 1–2 days.

When the lower respiratory tract becomes involved, the hypersecretion of mucus causes the moist cough, onset of respiratory distress and resultant feeding difficulties. As ability to feed in an infant is an important index of bronchiolitis severity, a careful history of a change in feeds is paramount.

Examination

Examination of the child will reveal a combination of signs of upper respiratory tract infection (URTI), along with signs indicative of lower respiratory tract infection (LRTI), which may fluctuate between examinations. The fever is usually low grade. A moist cough is common and wheeze may be audible at the bedside.

Tachypnoea and tachycardia are usually in proportion to the illness severity. Infants who are estimated to be feeding less than 50% of normal feeds usually have oxygen saturations less than 94%. Cyanosis is seen in children with severe disease.

Chest examination may reveal hyperinflation and recessions of the chest wall due to increased work of breathing. Paradoxically, as an infant fatigues, the recessions will decrease. In this situation the diminishing air entry signifies progressive disease. Auscultation reveals wheezes that are generally symmetrical. There may be inspiratory crepitations. The auscultation findings are dynamic as coughing will move secretions to more proximal airways, with resultant temporary clearing of the wheeze. A short time later, as the fluid returns to the more peripheral airways, the wheeze returns. Hence, babies referred by a local doctor with ‘marked wheeze’ may initially appear to be wheeze free when seen in the emergency department (ED) a short time later. Re-examination later will confirm the presence of wheeze.⁵

Oxygen saturations fall with disease severity and SaO₂ levels below 94% indicate a need for admission.⁴ McIntosh graded severity of bronchiolitis by simply documenting children as needing no oxygen, requiring oxygen and needing ventilation.⁶ Certainly, increasing oxygen requirements will be associated with increasing severity of disease.

Assessment

In helping to assess an infant with bronchiolitis and the likely subsequent course, one needs to determine the onset of the respiratory distress or poor feeding phase of the illness. Most children have increasing work of breathing for 48–72 hours due to increasing secretions, before a plateau phase followed by resolution over 3–7 days.