Bronchiolitis: assessment and evidence-based management

Viral bronchiolitis is the commonest lower respiratory tract infection in children less than 12 months of age and is the most frequent cause of hospitalisation in infants under 6 months of age.1,2 It is caused by viral infections of the lower respiratory tract, principally by respiratory syncytial virus (RSV), which gives rise to widespread small-airway narrowing due to airway oedema, resulting in air trapping.1-4 It is a self-limiting condition, but may be life threatening in a few, especially those with pre-existing cardiac or respiratory conditions.1,3,4 Treatment, when needed, is supportive in order to maintain adequate hydration and oxygenation.1,3 Useful antiviral therapy is unavailable.3 It has been suggested that infants with mildly reduced lung function are predisposed to developing bronchiolitis rather than developing slightly reduced lung function because they have had bronchiolitis.5 Infants who go on to develop recurrent bouts of wheezing in early childhood following bronchiolitis may do so because their airways are of smaller calibre6 or have altered compliance,7 and these children do not necessarily develop asthma by school age.5,6

Bronchiolitis is a clinical diagnosis. Typically, infants present with breathing difficulty associated with coryza.4,8,9 Less commonly, young infants, especially those born prematurely, may present with apnoea before developing the characteristic cough, tachypnoea and use of the accessory muscles of respiration.1,3,4,8 Most cases occur between late autumn and early spring, coinciding with the peak prevalence of RSV within the community.1,8-10 The clinical features of bronchiolitis are shown in Box 1. The range of symptoms and signs at presentation is reflected in the case scenarios of mild bronchiolitis and moderately severe bronchiolitis (Box 2).

The differential diagnosis of viral bronchiolitis may include pulmonary aspiration, bacterial or viral pneumonia, cardiac failure, cystic fibrosis, sepsis (with apnoea), primary ciliary dyskinesia, airway malacia (tracheomalacia and/or bronchomalacia), inhaled foreign body in an older infant, and pneumothorax.8 Differentiating viral bronchiolitis from transient early wheezing is often a source of confusion, especially in older infants and toddlers.2,6,11,12 Infants with transient early wheezing usually do not have bronchiolitis, but rather have viral-induced wheezing.2,11,12 Predisposing factors for transient wheezing in young children include maternal smoking in pregnancy, postnatal exposure to tobacco smoke, and reduced lung function (reduced airway resistance or increased dynamic compliance) before the development of any lower respiratory tract infection.2,11,12

As the hallmark of bronchiolitis is crackles (crepitations) on chest auscultation,13 the recurrence of wheezing as the predominant feature, and factors such as the presence of eczema in an older infant and a history of atopy or asthma in one or both parents, suggest that the infant is less likely to have viral bronchiolitis.11-13

Assessment of severity begins with adequate history-taking. It is important to inquire about pre-existing conditions, including premature birth, chronic respiratory conditions (eg, cystic fibrosis), underlying neurological or neuromuscular conditions, cardiac conditions and immunodeficiency, infectious contacts, duration and rate of progression of symptoms, and how well the infant is feeding (how long it takes to complete a feed, and, if the infant is breastfeeding, enquire if the mother feels that the breast is being emptied). In addition, ask whether the nappies have been as wet as usual in the preceding 12 to 24 hours.1,4,8,12

The examination should include surveillance of the following factors.1,4,8,12,13

General appearance: Is the infant tachypnoeic (> 60 breaths per minute), flushed and warm to touch (significantly febrile if temperature > 38.5°C) and tachycardic for age (generally heart rate > 140 beats per minute)? Is the infant having periods of apnoea?

Hydration: Is the nappy wet? Are the mucous membranes moist? Is the infant able to suck at the breast or on a bottle?

Degree of respiratory difficulty: Is the infant using accessory muscles to breathe? Are there crackles or wheezes evident on chest auscultation?

Adequacy of oxygenation: In room air, is the infant pink or centrally cyanosed?

The severity of bronchiolitis can be assessed as mild, moderate or severe (Box 3).1,3,8 Risk factors have been established for more severe bronchiolitis, and thus an increased likelihood of hospital admission (Box 4).14-16 The presence of one or more of these risk factors indicates the need for review within 24 hours by the general practitioner, or referral to an emergency department with paediatric expertise.

For children with mild bronchiolitis, no investigations are indicated, as they will not influence management [E3] (see Box 5 for key to evidence ratings).3,8 For moderate to severe bronchiolitis, the following investigations may be considered in a child in the emergency department [E3, E4].

• Oximetry;

• Nasopharyngeal aspirate for RSV and viral culture;

• Chest radiograph: if moderate (or more) respiratory difficulty, or if diagnostic uncertainty (eg, localised signs on chest auscultation or cardiac murmur with signs of congestive cardiac failure);

• Full blood count: if localised radiological changes are present together with neutrophilia on the blood count, then consider a diagnosis of bacterial pneumonia;

• Electrolyte, urea and creatinine levels, especially if the child needs intravenous fluids;

• Blood culture: if temperature > 38.5°C; and

• Blood gas levels: oximetry will guide adequacy of oxygenation, although the likelihood of CO2 retention is low for a child who requires an inspired oxygen concentration (Fio2) < 40%.18

Mild bronchiolitis requires explanation and reassurance, but no specific pharmacological or other therapy [E4] (Box 3).3,4 Bronchodilators and, to a lesser extent, systemic corticosteroids are frequently prescribed in general practice. However, randomised clinical trials of bronchodilators in viral bronchiolitis, whether in the outpatient setting or in hospitalised patients, have shown no clear or sustained benefits [E1].3,4,19 Much of the confusion over bronchodilators and corticosteroids in bronchiolitis relates to the fact that bronchiolitis, transient early wheezing and asthma can produce similar clinical features, especially in children aged over 9 to 12 months.8,11

Conversely, older infants with wheeze (who indeed may have asthma as well as or instead of a viral lower respiratory tract infection) and atopy may have a higher likelihood of responding to bronchodilators or a short course of oral corticosteroids [E4].11,12,20 If bronchodilators are considered, it is important to assess clinical response to a single trial dose before commencing potentially unnecessary treatment [E4]. Bronchodilators are most appropriately administered through a metered-dose inhaler and small-volume spacer or nebuliser rather than as an oral suspension.20

There is no role for nebulised corticosteroids in bronchiolitis [E2].21 Oral corticosteroids, if prescribed, should be limited to a 3-day course of prednisolone at a single daily dose of 1 mg/kg in those in whom a clinical diagnosis of asthma is made [E4].20 The difficulty remains in ascertaining what is asthma among a heterogeneous group of conditions associated with wheeze in early childhood.2,6,11 Reflecting this difficulty, one randomised controlled trial suggested that children aged 1 to 5 years with viral wheeze do not benefit from oral corticosteroids [E2].22

In the management of moderate to severe viral bronchiolitis in infants, “first principles” and common sense support the following recommendations [E4] (Box 3).1,3,4,8,23 Supplemental oxygen is the single most useful therapy, usually delivered via nasal prongs — care with feeding and minimal interference is required, and intravenous fluids are likely to be needed. Careful observation is necessary with high-risk and more unwell infants to facilitate timely introduction of ventilatory support in the few infants who will need it. Increasingly, this involves using mask or nasopharyngeal continuous positive airway pressure ventilation, which often obviates the need for endotracheal ventilation.