Bronchiolitis

Introduction

Bronchiolitis is an acute viral infection of the lower respiratory tract, affecting mainly infants under 2 years of age, with a peak between 3-6 months.

It is the most frequent lower respiratory infection in children within this age. It causes an obstruction of the wall of the bronchioles secondary to edema, mucus, and cellular debris; all of them, together with bronchospasm, increase the resistance of the small airways, leading to air trapping, overinflation, and, ultimately, atelectasis.

Respiratory Syncytial Virus (RSV) is the most common etiologic agent accounting for at least half of the cases. Other viruses detected in nasopharyngeal secretions from children hospitalized with bronchiolitis are rhinovirus, parainfluenza, human metapneumovirus (hMPV), bocavirus, coronavirus, influenza, and adenovirus, and coinfection has been described. There are no differences in the clinical presentation depending on the etiologic agent, although there can be some differences in the severity.

RSV is present worldwide, and 90% of the children will be infected in the first 2 years of life. It causes annual epidemics of bronchiolitis; the peak season varies amongst the countries depending on environmental and meteorological factors, but roughly occurs in wintertime and late spring: from November to March in the northern hemisphere, and from May to September in the southern hemisphere. In tropical countries, RSV may peak during rainy season.

To date, there is no etiologic treatment that shortens the course of the disease, being the cornerstone of the therapy the optimization of supportive and symptomatic measures.

As bronchiolitis has considerable morbi-mortality, several guidelines from different organisms are periodically published reviewing the best evidence to guide the clinicians in its management.

Clinical Presentation

The most common clinical presentation is that of an infant with a 3-4 days history of prodromal symptoms - coryza, mild fever, decrease in fluid intake - followed by a progression to lower airway symptoms -cough, respiratory distress with tachypnoea, chest recessions, and nasal flaring. Some other manifestations can be apnoeas, especially early in the course of the disease and sometimes the only manifestation in younger infants, and hypothermia, most frequent in the first two months of life.

On examination, the child can appear from having a good general condition to being miserable or even lethargic, with a variable degree of severity in the respiratory symptoms: from mild tachypnoea to air hunger and dyspnoea, with chest recessions, nasal flaring, and grunting. There can be fine rales, wheezes, and decrease air entry on auscultation.

Assessment

Once diagnosed, the next step is to assess the severity, defined as those signs and symptoms associated with poor feeding and respiratory distress characterized by tachypnea, nasal flaring, and hypoxemia.

The parameters to focus on are:

• The ability of the child to maintain effective breathing- using clinical parameters and complementary tests, such as pulse oximetry or capillary/arterial blood gas in case of severe respiratory symptoms including apnoeas. To date, some clinical scores have been developed in an attempt to predict the course of the disease, but none has been validated to be used universally.

• Ability of the child to maintain adequate hydration- assessment of clinical signs of dehydration, fluid intake, and diuresis, such as the presence of a wet nappy in the last 12 hours, with complementary tests if needed, like biochemistry or blood gas.

• The presence of risk factors associated with a more severe presentation and higher mortality:
  

  • Chronic lung disease, including bronchopulmonary dysplasia defined as preterm infants <32 weeks of gestation who require >21% oxygen for at least the first 28 days of life
  • Haemodynamically significant congenital heart disease
  • Chronological age, particularly under 3 months
  • Premature birth, particularly under 32 weeks
  • Neuromuscular disorders
  • Immunodeficiency

Diagnosis

The diagnosis of acute bronchiolitis is clinical; an infant who presents with the above symptoms and physical examination in an epidemiological context doesn´t need further tests to be diagnosed.

The differential diagnosis is:

• Viral induce wheeze
• Asthma
• Infectious pneumonia
• Mucociliary clearance disorders: cystic fibrosis, primary ciliary dyskinesias, and bronchiectasis
• Anatomic abnormalities: congenital structural airway anomaly, extrinsic abnormalities resulting in compression
• Aspiration syndromes: gastroesophageal reflux disease, pharyngeal-swallow dysfunction

Investigations

Some tests might be advisable to assess the degree of severity, the presence of complications or to rule out an alternative diagnosis.

Imaging

Chest X-ray shows hyperinflated lungs with patchy atelectasis. It is not advisable to be routinely done when the patients present a clear diagnosis of bronchiolitis, as the findings could be misleading of bacterial pneumonia. However, it is recommended if the latter is suspected in the presence of high fever or focal crackles on auscultation. It can also show the presence of respiratory complications if worsening of the symptoms, such as pneumothorax, or in the case of congenital abnormalities.

Laboratory

Routine full blood count or biochemistry is not recommended. The most frequent findings are normal or high lymphocyte count with normal C reactive protein. In the case of neutrophilia with high inflammatory markers, the bacterial infection should be suspected.

Arterial blood gas should be done in cases suggestive of respiratory failure.

Microbiology

Samples should not be routinely taken, as there is no increased benefit of identifying a specific viral etiology for the patient. It could be useful for epidemiological or isolation purposes.

There is no need for a sepsis evaluation in case the diagnosis of bronchiolitis is clear, as the presence of a concurrent bacterial infection is highly unlikely in these patients.

Bronchiolitis Next Steps

Once the assessment of the severity is done, the question is whether the child can be safely discharged home or needs hospital admission.

As has been already mentioned, the therapy is focused on symptomatic relief and supportive measures; however, the management between physicians can differ widely. To assist in the decision-making process, several guidelines are released periodically by different organisms (i.e. AAP, NICE, the own Trusts), using the best evidence available at the time although with subtle differences amongst their recommendations.

Pharmacological Agents

The routine use of antivirals (i.e. ribavirin) is not recommended, although it could be considered in some specific patients with risk factors. Some other agents have been studied throughout the years based on the pathophysiology of the disease: adrenaline, bronchodilators -salbutamol, montelukast, ipratropium bromide-, systemic or inhaled corticosteroids, and hypertonic saline. The current evidence for each of them is:
Adrenaline- large, multicenter, randomized trials have not shown improvement in outcome among these patients.

Bronchodilators- randomized trials have not shown a consistent beneficial effect on disease resolution, need for hospitalization, or length of stay.

Corticosteroids- large, multicenter, randomized trials provide clear evidence of lack of benefit.

Nebulized hypertonic (3%) saline- it may improve symptoms of mild-to-moderate bronchiolitis if the length of stay is >3 days.

Due to the above results, to date, none of them are routinely recommended, being the only exception the consideration of using nebulized hypertonic saline in hospitalized patients made by the AAP.

Non-pharmacological Agents

Focused on improving oxygenation and hydration.

• Ensure patient comfort and monitoring- repositioning can decrease the work of breathing. Periodic assessment of vital signs and hydration. Continuous pulse oxymetry is not necessary as there is a very poor correlation between respiratory distress and oxygen saturations in these infants. If there are signs of exhaustion, for example, listlessness or decreased respiratory effort, recurrent apnoea, or failure to maintain adequate oxygen saturation despite oxygen supplementation, a capillary blood gas should be performed and admission to a Paediatric Intensive Care Unit (PICU) must be considered.
• Removal of obstructive secretions- using nasal drops or upper airway suctioning. The latter is not to be routinely used, as it can be distressing; however, as children are obligate nasal breathers, it could be used in those whose upper airway secretions contribute to respiratory distress or feeding difficulties.
• Physiotherapy-not to be routinely used. It could be considered in those patients with comorbidities who might have difficulty clearing secretions such as those with spinal muscular atrophy or severe tracheomalacia.
• Supplemental oxygen- in those children with persistent hypoxemia. The cut-offs differ from the guidelines consulted: SpO2<92% (NICE) or <90% (AAP).
• Continuous positive airway pressure (CPAP)- in cases of impending respiratory failure.
• Supportive fluid management- orogastric or nasogastric feed for those with inadequate oral intake or intravenous fluids for those who cannot tolerate enteral feed or in those with respiratory failure.

Management

• A child who is able to tolerate fluids with orogastric feeds and does not have any signs or symptoms of severity, can be discharged home providing that the caregivers are able to look after the patient:
  
  • Having been given key safety information

  • Ensuring appropriate fluid intake

  • Recognizing red flag symptoms and seeking urgent professional review if any of them develop

• A child should be admitted to the hospital if any of the following is present:
  
  • Apnoea (observed or reported)

  • Persistent oxygen saturation of less than 92% when breathing air

  • Inadequate oral fluid intake (50-75% of usual volume, taking account of risk factors and using clinical judgement)

  • Persisting severe respiratory distress

In this case, the above non-pharmacological measures should be used, and nebulized hypertonic saline could be considered.

Prognosis

Most children recover in spite of the lack of etiologic treatment. A peak in the severity of the symptoms is expected after 48-72 hours of the onset, and the resolution is variable within a median of 12 days. Having said that, some residual manifestations, such as mild cough, can take some weeks to disappear.

The case fatality rate is <1%, with death attributable to apnoea, respiratory arrest, or severe dehydration. Other complications are uncommon.

The immunity developed against RSV is not permanent so reinfections can occur.

Severe bronchiolitis early in life is associated with an increased risk of asthma; however, whether the viral infection is contributing to the development of asthma or whether there is a predisposition to suffer both of them remains elusive in spite of the investigations.

Prevention

There are investigations for the development of a safe and effective vaccine against RSV, but, to date, the research has not been entirely successful. Therefore, the best tool for prevention is decreasing the exposure to and transmission of the respiratory viruses known to cause acute bronchiolitis. Most of them are spread by contact with secretions, while adenovirus and influenza are transmitted also by droplets.

Hand disinfection is the most effective measure to control the spread of the infection. All people should disinfect hands before and after direct contact with patients, after contact with inanimate objects in the direct vicinity of the patient, and after removing gloves, using preferentially an alcohol-based rubs for hand decontamination or soap and water.

Exclusive breastfeeding should be encouraged for at least 6 months to decrease the morbidity of respiratory infections.

Smoking increases the risk of severe bronchiolitis. Caregivers should be counseled about exposing the patient to environmental tobacco smoke and smoking cessation.

Palivizumab is a humanized mouse IgG1 monoclonal antibody directed against a conserved epitope on the surface fusion protein of RS. It is recommended to reduce the severity and incidence in selected children such as infants with hemodynamically significant heart disease or chronic lung disease of prematurity in the first year of life, given as a maximum of 5 monthly doses (15 mg/kg/dose) during the RSV season. For other conditions (i.e. immunodeficiency, neuromuscular disorders, cystic fibrosis) it could be considered.