Paediatrics

Bronchiolitis

An acute viral small-airway infection in babies and young children causing coryza, cough, tachypnoea, wheeze or crackles and feeding difficulty; treatment is supportive, with escalation driven by work of breathing, hydration, apnoea and oxygenation.

Definition

Bronchiolitis is an acute viral lower respiratory tract infection in babies and young children causing inflammation and obstruction of the small airways, usually after a coryzal prodrome.

Epidemiology

Bronchiolitis occurs mainly in children under 2 years and most commonly in the first year, peaking between 3 and 6 months. Most cases are managed at home, but young age, prematurity and cardiopulmonary, neuromuscular or immune disease increase the risk of severe illness.

Pathophysiology

Viral infection causes bronchiolar epithelial injury, mucosal oedema, mucus and cellular debris. In a small infant airway this produces widespread airflow obstruction, air trapping and ventilation-perfusion mismatch. Increased work of breathing and nasal secretions impair feeding; severe disease progresses to apnoea, exhaustion and respiratory failure.

First principles

Bronchiolitis is a clinical syndrome of small-airway inflammation

In babies and children under 2 years, a 1-to-3-day coryzal prodrome followed by persistent cough, tachypnoea or chest recession, and wheeze or crackles supports the diagnosis. Respiratory syncytial virus is common, but the diagnosis is clinical and does not require naming the virus.^1,2

Feeding is a severity marker

Tachypnoea, nasal obstruction and increased work of breathing make coordinated sucking and breathing difficult. Reduced oral intake is therefore both a sign of respiratory burden and a route to dehydration; assess it alongside respiratory effort rather than treating it as a minor symptom.^1,3

Apnoea may be the first sign in a young infant

Infants, particularly those under 6 weeks or born prematurely, may present with observed or reported apnoea without prominent chest signs. Recurrent apnoea, exhaustion or failure to maintain oxygenation despite oxygen suggests impending respiratory failure and needs urgent escalation.^1,3

The treatment is supportive, not bronchodilator-based

Bronchiolitis is not routine infant asthma. NICE advises against salbutamol, nebulised adrenaline, ipratropium, montelukast, corticosteroids, hypertonic saline and antibiotics because these do not improve the course of uncomplicated bronchiolitis. Support oxygenation and hydration while the illness resolves.¹

Escalation depends on the whole child

Pulse oximetry thresholds are age- and risk-dependent, but no single saturation should override the clinical picture. Consider work of breathing, apnoea, exhaustion, hydration, comorbidity, age, prematurity, carer capability and distance from healthcare when deciding referral, admission and discharge.^1,4

Presentation

Usually a baby or young child with 1 to 3 days of coryza followed by persistent cough, tachypnoea or recession, widespread wheeze or crackles, and reduced feeding. Symptoms commonly peak around days 3 to 5; cough may persist for several weeks.^1,2

Cardinal features

Coryzal prodrome for 1 to 3 days
Persistent cough with tachypnoea or chest recession
Widespread wheeze or fine crackles
Increased work of breathing, nasal flaring or feeding difficulty
Fever is often absent or low grade
Apnoea may occur without other obvious signs in very young infants

Red flags

Observed or reported apnoea
Central cyanosis or a baby who looks seriously unwell
Severe respiratory distress, grunting, marked recession or respiratory rate over 70 breaths/minute
Exhaustion, listlessness, reduced respiratory effort or failure to maintain oxygenation despite oxygen
Inadequate oral intake, clinical dehydration or no wet nappy for 12 hours
Persistent oxygen saturation below the relevant referral, admission or oxygen threshold
Young age, prematurity, chronic lung disease, significant congenital heart disease, neuromuscular disease or immunodeficiency

Investigations

Clinical respiratory assessment

Bronchiolitis is diagnosed from the age, prodrome and respiratory pattern. Assess respiratory rate, work of breathing, recession, grunting, colour, alertness, apnoea history, air entry, wheeze or crackles and response over time. A falling respiratory rate with worsening effort can signal exhaustion rather than improvement.

Expected finding: Coryza followed by cough, tachypnoea or recession, and widespread wheeze or crackles; focal signs or high fever should prompt consideration of pneumonia or another diagnosis.

^1,3

Pulse oximetry

Measure oxygen saturation in every baby or child presenting to secondary care with clinical evidence of bronchiolitis, and in primary care when available. Use an appropriately sized probe and trained technique; borderline values need clinical correlation because readings can be inaccurate.

Expected finding: Saturation may be normal or reduced. Persistent hypoxaemia is one part of the referral, admission and oxygen decision, alongside work of breathing and risk factors.

^1,5

Feeding and hydration assessment

Document usual and current oral intake, wet nappies, mucous membranes, tears, capillary refill, weight where useful and clinical signs of dehydration. Intake around 50% to 75% of usual volume is a referral or admission concern when combined with clinical judgement and risk factors.

Expected finding: Reduced intake and fewer wet nappies in moderate or severe disease; dehydration or inability to feed safely requires fluid support and may require admission.

^1,3

Blood tests and chest radiograph only when clinically indicated

Do not routinely perform blood tests or chest X-ray. Radiographic changes may mimic pneumonia and should not be used to decide on antibiotics. Consider chest X-ray if intensive care is being proposed, and investigate for sepsis, pneumonia, congenital heart disease or another cause when the clinical picture is atypical.

Expected finding: No routine test result is expected in uncomplicated bronchiolitis; focal crackles with high fever, shock, persistent deterioration or an atypical course redirects investigation.

^1,5

Capillary blood gas in severe deterioration

Do not routinely perform blood gas testing. Consider capillary blood gas when respiratory distress is severe and worsening, supplemental oxygen concentration is over 50%, or impending respiratory failure is suspected, while escalating paediatric support in parallel.

Expected finding: Hypercapnia, acidosis or hypoxaemia may support impending respiratory failure, but treatment must be guided by the clinical state and response rather than a single gas.

Management

Step	Detail	Source
Assess severity and choose home or hospital care	Assess work of breathing, apnoea, colour, alertness, oxygen saturation, hydration and oral intake, then consider age, prematurity, chronic lung disease, significant congenital heart disease, neuromuscular disease, immunodeficiency and carer circumstances. Refer immediately for apnoea, central cyanosis, severe respiratory distress or a seriously unwell appearance. Consider hospital referral for respiratory rate over 60, inadequate intake, dehydration or persistent oxygen saturation below 92% in air.^1,4,3	NICE NG9 recommendations 1.2.1 to 1.3.5, updated 2021
Provide supportive respiratory care	Use minimal handling and monitor respiratory effort and oxygenation. Give supplemental oxygen if saturation is persistently below 90% in children aged 6 weeks and over, or below 92% in babies under 6 weeks or children of any age with an underlying health condition. Consider CPAP and urgent paediatric critical-care input for impending respiratory failure, including exhaustion, recurrent apnoea or failure to maintain oxygenation despite oxygen.^1,5	NICE NG9 recommendations 1.1.10, 1.4.4 and 1.4.5, updated 2021
Use suction selectively	Do not routinely perform upper-airway suctioning. Consider it when secretions are causing respiratory distress or feeding difficulty, and perform it in a baby or child presenting with apnoea even if secretions are not obvious. Do not perform routine chest physiotherapy unless a relevant comorbidity such as spinal muscular atrophy or severe tracheomalacia creates additional difficulty clearing secretions.¹	NICE NG9 recommendations 1.4.1 to 1.4.8
Support hydration and feeding	If the child cannot take enough fluid orally, give fluids by nasogastric or orogastric tube. Give intravenous isotonic fluids when enteral fluids are not tolerated or when impending respiratory failure is present, using the current NICE paediatric fluid guidance and local monitoring pathway.¹	NICE NG9 recommendations 1.4.11 and 1.4.12
Avoid ineffective routine medicines	Do not use antibiotics, salbutamol, nebulised adrenaline, hypertonic saline, montelukast, ipratropium bromide, systemic corticosteroids, inhaled corticosteroids or combined systemic corticosteroid and nebulised adrenaline therapy for uncomplicated bronchiolitis. Reconsider the diagnosis if there is high fever, focal crackles, recurrent episodic wheeze or another indication for targeted treatment.¹	NICE NG9 recommendation 1.4.3
Discharge safely and give explicit safety-netting	Before discharge, ensure the child is clinically stable, taking adequate oral fluids and has maintained oxygen saturation in air for 4 hours including sleep: over 90% if aged 6 weeks and over, or over 92% if under 6 weeks or with an underlying health condition. Give carers written advice to seek immediate help for worsening work of breathing, intake 50% to 75% of normal, no wet nappy for 12 hours, apnoea, cyanosis or exhaustion; advise that nobody smokes in the home and arrange follow-up when needed.^1,3,5	NICE NG9 recommendations 1.5.1 to 1.6.1, updated 2021

Illustrations

Obstructed bronchiole cross-sectionComparative diagram of a normal versus an inflamed infant bronchiole showing how mucosal oedema and debris narrow a small airway.PassFinals · original

Infant respiratory distress signsIllustration of intercostal and subcostal recession, nasal flaring and tracheal tug used to assess severity.PassFinals · original

Chest X-ray of hyperinflationChest radiograph showing hyperinflation and patchy atelectasis; imaging is not routinely required but is shown for teaching when intensive care or an alternative diagnosis is being considered.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0

Differentials

Viral-induced wheeze or early-onset asthma

Persistent wheeze without crackles, recurrent episodic wheeze or atopic history, particularly in an older infant or young child.

Pneumonia

High fever over 39°C and/or persistently focal crackles; reassess the diagnosis and manage suspected sepsis when clinically indicated.

Pertussis

Paroxysmal cough, whoop, post-tussive vomiting or apnoea, especially with an epidemiological or immunisation clue.

Foreign-body aspiration

Sudden onset after choking with focal or unilateral chest signs rather than a coryzal prodrome.

Congenital heart disease or heart failure

Poor growth, hepatomegaly, murmur, sweating or breathlessness with feeds, or a course not explained by a viral respiratory illness.

Complications

Hypoxaemia requiring supplemental oxygen
Apnoea, particularly in young or premature infants
Dehydration and inadequate nutrition from feeding difficulty
Impending respiratory failure requiring CPAP or intensive care
Diagnostic error such as missed pneumonia, sepsis, congenital heart disease or foreign-body aspiration

Prognosis

Symptoms often peak between days 3 and 5. Most children recover with supportive care; cough commonly resolves within 3 weeks, although some take longer. A minority need hospital care for oxygen, hydration or respiratory support, and risk is higher in very young, premature or medically complex children.

Guidelines

Bronchiolitis in children: diagnosis and management (NG9) (NICE, 2025)

References

Evidence checked: 2026-08-03

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.