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Bronchiolitis is an inflammation of the bronchioles which causes narrowing of the lower respiratory tract and a build-up of mucus. It is a common respiratory condition in infants, with approximately one-third of infants developing bronchiolitis before the age of one. The highest incidence usually occurs between the ages of three to six months.

Bronchiolitis is commonly seen during the winter season, and usually persists for seven to ten days.


Bronchiolitis is generally caused by a viral infection; the majority of cases are caused by respiratory syncytial virus (RSV). Other viruses which may lead to bronchiolitis include parainfluenza virus, rhinovirus, adenovirus, influenza, and human metapneumovirus.

Risk Factors

Children may be admitted to hospital with severe bronchiolitis if they have certain risk factors, such as chronic lung disease, congenital heart disease, prematurity, Down Syndrome, or cystic fibrosis. Additionally, younger than three months old and neuromuscular disease also increase the risk.

Clinical Features


Typical symptoms of bronchiolitis include persistent cough, wheeze, shortness of breath, fever, runny nose, cold, and the worsening of symptoms during the second or third night of illness.

Other symptoms may include apnoea (in infants younger than six weeks of age), difficulty feeding, and dehydration in severe cases.

Other important areas to cover when taking the history include past medical history, medications/allergies, family history, and social history. Ask about known risk factors, atopic conditions, parental smoking, the child's home situation, and any illness in the family.

Clinical Examination

Typical Clinical Findings of bronchiolitis include:

  • Bilateral polyphonic expiratory wheeze
  • Tachypnoea
  • Tachycardia
  • Low-grade fever (<39o)
  • Irritability

Other Clinical Findings can include:

  • Prolonged capillary refill time (>2 seconds)
  • Cyanosis
  • Signs of dehydration -dry mucous membranes, sunken fontanelle in young babies5
  • Reduced conscious level6
  • Recessions (intercostal, subcostal or sternal) –Increased work of breathing visibly on external due to compliant rib cage.

Differential Diagnoses

Table 1. Differential diagnoses of bronchiolitis

Differential diagnosisFeatures differentiating from bronchiolitisPneumonia

  • Fever >39o
  • Focal crackles

Viral-induced wheeze

  • Persistent wheeze without crackles
  • Recurrent wheeze associated with a viral illness
  • Personal or family history of atopy
  • >1-year-old
  • Responsive to salbutamol treatment

Early-onset asthma

  • Persistent wheeze without crackles
  • Recurrent wheeze associated with triggers
  • Personal or family history of atopy
  • >1-year-old
  • Responsive to salbutamol treatment

Bordetella pertussis or whooping cough

  • Coryza
  • Characteristic hacking cough followed by an inspiratory ‘whoop’
  • Unvaccinated

Gastro-oesophageal reflux

  • Chronic cough
  • Poor weight gain

Foreign body aspiration

  • May have a history of choking
  • Monophonic wheeze

What is Bronchiolitis?

Bronchiolitis is a condition caused by narrowing of the lower respiratory tract due to inflammation of the bronchioles and build-up of mucus. It is usually caused by a viral infection, with around 80% of cases caused by the respiratory syncytial virus (RSV).


Children are diagnosed clinically with bronchiolitis if they present with coryzal symptoms such as a persistent cough and tachypnoea or chest recession, accompanied by wheeze or crackles heard on chest auscultation. Investigations do not influence the treatment of bronchiolitis.

Bedside Investigations

  • Pulse oximetry: children should be admitted if oxygen saturation is <92%

Laboratory Investigations

  • Blood tests (including arterial blood gases): these are not routinely performed


  • Chest X-ray: not routinely performed, but can be used to rule out pneumonia or pneumothorax if there is an area of the lung with reduced air entry or focal crackles.


Bronchiolitis is typically self-limiting, but may require admission to hospital in certain cases. The criteria for admission depends on factors such as apnoea, reduced oxygen saturation, reduced oral intake and presence of risk factors for severe disease. Management is supportive and typically involves oxygen supplementation, positive pressure, nutritional and fluid supplementation, and support for smoking cessation.

Bronchodilators and antibiotics are not effective as the narrowing is due to increased secretions, not bronchoconstriction.


Complications of bronchiolitis can include clinical dehydration, Syndrome of inappropriate antidiuretic hormone (SIADH) and hyponatraemia, and apnoea and respiratory failure requiring intubation and ventilation.

Key Points

  • Bronchiolitis is characterised by narrowing of the lower respiratory tract due to inflammation of the bronchioles and build-up of mucus.
  • Bronchiolitis is usually caused by a viral infection. About 80% of cases are caused by the respiratory syncytial virus (RSV).
  • The diagnosis is clinical, with investigations rarely indicated.


Bronchiolitis is generally self limiting and not all children suffering from it will need to be admitted to a hospital. Supportive management is essential, such as oxygen supplementation, high flow oxygen and treatment of dehydration. Possible complications include: dehydration, SIADH, apnoea and respiratory failure.


  1. Patient. Bronchiolitis. Published in 2018. Available from: LINK.
  2. Goldstein H. Published in 2013. Available from: LINK.
  3. Spottingthesickchild. Symptoms: Difficulty in Breathing. Published in 2020. Available from: LINK.
  4. NICE Guidelines. Bronchiolitis in children: diagnosis and management. Published in 2015. Available from: LINK.
  5. Bronchiolitis (and RSV) in infants and children (Beyond the Basics). Published in 2019. Available from: LINK.
  6. West Sussex Children & Young People's Urgent Care Network. Bronchiolitis Pathway and Assessment in Acute Settings for Children 0-2 years. Published in 2011. Available from: LINK.
  7. Wikimedia Commons. Intercostal recessions in a newborn with breathing difficulties. License: CC BY-SA. Available from: LINK.
  8. Bronchiolitis in Infants and Children: Clinical Features and Diagnosis. Published in 2020. Available from: LINK.


Dr Hannah Murch

Paediatric Emergency Medicine Consultant


Arunachalam Soma

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