Bronchiolitis

Introduction

Bronchiolitis is a viral infection of the bronchioles, the smallest air passages in the lungs. It is most commonly caused by respiratory syncytial virus (RSV) (1). Respiratory syncytial virus accounts for 60–80% of bronchiolitis presentations (2). Other viruses such as human rhinovirus and coronavirus could be etiological agents (3).

Epidemiology

Bronchiolitis is a common disease that usually affects children under the age of 2. About 1/3 of children will develop clinical bronchiolitis in their first year of life (4), although up to 50% may have encountered RSV by this time.  It mainly occurs during the winter and spring months (5). In recent years, hospital admissions due to bronchiolitis have increased (6). Around 2-3% of children require admission to hospital due to bronchiolitis during winter (7).

Pathophysiology

Bronchioles are airways in the lungs which are less than 2mm wide and do not contain cartilage or submucosal glands. There are several physiological changes which occur in response to viral infection:

• Proliferation of goblet cells causing excess mucus production
• IgE-mediated type 1 allergic reaction causing inflammation
• Bronchiolar constriction
• Infiltration of lymphocytes causing submucosal oedema
• Infiltration of cytokines and chemokines

The combination of mucus, oedema and increased cells in the bronchioles leads to a ball-valve effect resulting in hyperinflation, increased airway resistance, atelectasis (lung collapse) and ventilation-perfusion mismatch, which together result in the clinical features typically seen in bronchiolitis (1).

Risk factors

• Being breast fed for less than 2 months
• Smoke exposure (eg. parents’ smoke)
• Having siblings who attend nursery or school (increased risk of exposure to viruses)
• Chronic lung disease due to prematurity (8)

Clinical features

History

The typical history is one of increasing symptoms over 2-5 days, usually consisting of:

• Low-grade fever
• Nasal congestion
• Rhinorrhoea
• Cough
• Feeding difficulty

On examination

• Tachypnoea
• Grunting
• Nasal flaring
• Intercostal, subcostal or supraclavicular recessions
• Inspiratory crackles
• Expiratory wheeze
• Hyperinflated chest
• Cyanosis or pallor (9)

Differential diagnosis

• Pneumonia
• Croup
• Cystic fibrosis
• Heart failure – VERY IMPORTANT not to miss this, and it can be difficult to diagnose
• Bronchitis (10)

Investigations

It is important to perform pulse oximetry on all children with suspected bronchiolitis.

Laboratory tests

• Nasopharyngeal aspirate or throat swab – RSV rapid testing and viral cultures
• Blood and urine culture if child is pyrexic
• FBC
• Blood gas (ABG) if severely unwell – this may detect respiratory failure and the need for respiratory support, but should not be done routinely

Imaging

• CXR (only if diagnostic uncertainty or atypical course) – features seen are:
  • Hyperinflation
  • Focal atelectasis
  • Air trapping
  • Flattened diaphragm
  • Peribronchial cuffing (11)

Management

The first decision is whether the child should be managed at home or in hospital. This should be based on any comorbidities the child may have and any factors which may affect the carer’s ability to look after a child with bronchiolitis. Most can be managed at home with supportive measures eg. fluids, good nutrition and temperature control (11). Literature has shown there is no evidence of benefit from the use of mist, nebulised hypertonic saline, antibiotics, corticosteroids or bronchodilators. Physiological studies and clinical trials support the notion that salbutamol and other bronchodilators have no impact on wheeze in bronchiolitis. From this, it has erroneously been concluded that there are no β-adrenoceptors in the infant lung (12).

An urgent referral to hospital should be made if any of the following features are seen (6):

• Apnoea
• Child looks seriously unwell
• Severe respiratory distress eg. grunting, marked recessions, respiratory rate >70
• Central cyanosis
• Oxygen sats < 92%

Hospital referral should be considered if any of the following are seen (6):

• Respiratory rate > 60
• Inadequate fluid intake (50-75% of usual volume)
• Clinical dehydration

In hospital, the following management steps should be taken (6):

• Give oxygen if sats < 92% in room air
• Give fluids via nasogastric or orogastric tube if inadequate oral intake
• Consider CPAP if there is impending respiratory failure
• Perform upper airway suctioning if there are upper airway secretions or apnoea

Discharge can be considered when the child is:

• Clinically stable
• Taking adequate oral fluids
• Maintaining sats > 92%

As stated previously, there is no role for antibiotics, steroids or bronchodilators in the treatment of bronchiolitis.

Complications

These complications can occur following bronchiolitis (8, 9):

• Hypoxia
• Dehydration
• Fatigue
• Respiratory failure
• Persistent cough or wheeze (very common and parents should be counselled that their child may cough for several weeks)
• Bronchiolitis obliterans – Airways become permanently damaged due to inflammation and fibrosis (13)

Prognosis

Bronchiolitis is a self-limiting infectious process. Bronchiolitis usually lasts 7-10 days (14). Most children who require hospital admission can cough for up to 6 weeks, whereas those cared for at home will have a more minor ‘common cold’. When the disorder is recognized and treated, the prognosis is excellent. The majority of children recover without any adverse effects. About 3% of infants will require admission to the hospital, and the mortality rates vary from 0.5% to 7% (15).

References

Authors:

1st Author: Trainee Doctor Hannah Murray

Senior Reviewer: Dr Matthew Hurley (Respiratory paediatric consultant)

Student Reviewer: Luke Austen

Update: Dr Alex Tom (paediatric trainee)