Bronchiolitis

Overview

Acute viral lower respiratory tract infection causing inflammation and oedema of the bronchioles. Leading cause of hospitalisation in infants under 1 year; peak incidence 3-6 months; seasonal (November-March).

Aetiology

•RSV - accounts for ~70-80% of cases

•Others: rhinovirus, parainfluenza, human metapneumovirus, adenovirus, coronavirus

Presentation

•Prodrome (days 1-3): coryzal symptoms - runny nose, sneezing, low-grade fever

•Cough - dry, persistent, may be paroxysmal

•Wheeze - expiratory, polyphonic

•Tachypnoea - most sensitive sign of lower respiratory tract involvement

•Recession - subcostal and intercostal; reflects increased work of breathing

•Fine inspiratory crackles on auscultation

•Hyperinflation - barrel chest, liver pushed down; reflects air trapping

•Poor feeding - due to increased respiratory rate disrupting suck-swallow-breathe coordination

•Apnoea - particularly in infants <2 months and ex-premature infants

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Apnoea may be the FIRST presenting feature of bronchiolitis in infants under 2 months or born prematurely - do not wait for wheeze or recession before admitting a young infant with apnoea.

Investigations

•Bronchiolitis is a clinical diagnosis - routine investigations not required in typical uncomplicated cases

•Essential: pulse oximetry - guides oxygen need and admission decision

•Nasopharyngeal aspirate (NPA) for RSV PCR/immunofluorescence - for infection control cohorting only, not required for management

•Chest X-ray - not routine; consider if diagnosis uncertain, failing to improve, or life-threatening disease. May show hyperinflation, peribronchial thickening, patchy atelectasis

•Blood gas - if significant distress, persistent low saturations, or HFNC/CPAP being considered

•FBC/CRP - only if secondary bacterial infection or sepsis suspected

Management

Management is supportive. Community management is appropriate for mild cases with good feeding, no significant recession, and saturations >92% in air.

First-line · All admitted infants

1. 1Nasal saline drops and gentle suction - clear secretions before feeds
2. 2Supplemental oxygen via nasal cannula or face mask - target saturations ≥92% (some centres ≥94%); humidified preferred
3. 3Hydration support - frequent small feeds; nasogastric (NG) feeds if oral intake <50-75% of normal or unsafe due to respiratory rate; IV fluids if NG not tolerated

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Second-line · Failing standard oxygen

1. 1High-flow nasal cannula (HFNC) oxygen (e.g. Optiflow) - reduces work of breathing via positive distending pressure and nasopharyngeal dead space washout

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Third-line · Respiratory failure / PICU

1. 1CPAP or mechanical ventilation - for respiratory failure, persistent apnoea, or rising CO2

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Do NOT use in bronchiolitis: salbutamol or bronchodilators, prednisolone or systemic corticosteroids, routine antibiotics, or nebulised hypertonic saline (3%) - evidence shows no benefit and potential harm.

Prevention

•Palivizumab - humanised monoclonal antibody against RSV fusion protein; monthly IM injection October-February (up to 5 doses); reduces RSV hospitalisation by ~55%

•Indicated for: infants born <35 weeks gestation, haemodynamically significant congenital heart disease, chronic lung disease of prematurity requiring ongoing treatment

•RSV maternal vaccine (Abrysvo) - approved MHRA 2023; given 24-36 weeks gestation for passive infant protection

Complications

•Apnoea - most dangerous; may be first sign in young/premature infants

•Respiratory failure - requiring escalation to HFNC, CPAP, or ventilation

•Dehydration - from poor oral intake and increased insensible losses

•Secondary bacterial infection - consider if unexpected deterioration after initial improvement or persistently high fever

•Recurrent wheeze/asthma - long-term association; do not diagnose asthma during or immediately after bronchiolitis episode

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Cough may persist up to 4 weeks - counsel parents at discharge. Provide safety-netting: return if worsening breathing, apnoea, reduced wet nappies, or significantly reduced feeding.

Risk factors for severe disease

High-risk groups

Age <6 weeks

Prematurity (<35 weeks)

Congenital heart disease (haemodynamically significant)

Chronic lung disease of prematurity

Immunodeficiency

Neuromuscular disease

Admission criteria

Admit if any of the following present

SpO2 persistently <92% in air

Apnoea (observed or reported)

RR >70 breaths/min

Severe recession or grunting

Feeding <50-75% of normal intake

Age <6 weeks

Significant risk factors for severe disease

Clinical deterioration despite home supportive care