Bronchiolitis

The college loves bronchiolitis. Of the four questions in the past papers, three were unequivocally about bronchiolitis (eg. "A 12-month-old infant is admitted to your ICU with bronchiolitis"). The other SAQ had a patient with bronchiolitis, but the discussion strayed into the wider territory of respiratory failure. Bronchiolitis has therefore featured in 20% of the past paper paeds questions (because there haven't been that many paediatric SAQs -understandably, in this adult intensive care exam). It is therefore an important topic to revise in the pre-dawn panic of Day 0.

Those SAQs:

• Question 11 from the first paper of 2016
• Question 7 from the second paper of 2011 (not really just about bronchiolitis)
• Question 6  from the first paper of 2009
• Question 28 from the first paper of 2008

For background reading, one may pay for the UpToDate articles on bronchiolitis, or read the free "Clinical practice guideline: the diagnosis, management, and prevention of bronchiolitis" from the American Academy of Pediatrics. Both sources were used in the making of this summary.

Definition of bronchiolitis

To call it "bronchiolitis", your infant needs to have the following features:

• Age under 2
• Upper respiratory prodrome, eg. rhinorrhoea
• Lower respiratory features, eg. wheeze and creps
• Increased respiratory effort

Histologically, there is acute inflammation, edema, and necrosis of epithelial cells lining small airways, and increased mucus production. Wheeze is an important clinical feature but overlaps with asthma and "recurrent virus-induced wheezing" which is apparently a serious paediatric diagnosis. For the purposes of bronchiolitis reasearch, you've got to do better than that. Researchers have developed a series of more functional definitions. For instance, in the study by Plint et al (2009) which investigated the benefits of dexamethasone, bronchiolitis was defined as "the first episode of wheezing associated with signs of an upper respiratory tract infection during the peak RSV season".

 RSV is in fact the most common pathogen. Other possibilities include rhinovirus, influenza, parainfluenza, human metapneumovirus, human bocavirus, adenovirus and coronavirus (which could extend towards SARS and MERS).

Question 11 from the first paper of 2016 asked for five differential diagnoses. The whole table of differentials for respiratory failure in children was reproduced in the discussion section. However, there are specific broncholitis mimics which need to be mentioned, as they also present with wheeze. 

These are:

• Asthma
• Recurrent viral-triggered wheezing
• Bacterial pneumonia
• Chronic lung disease of ex-prematurity (or some other sort of chonic lung disease)
• Foreign body aspiration
• Aspiration pneumonia
• Congenital heart disease with heart failure
• Vascular rings (eg. pulmonary artery slings)

Clinical features

• Fever
• Rhinorrhea
• Cough
• Tachypnea
• Wheeze
• Creps in the chest
• Features of increased respiratory effort:
  • Grunting
  • Nasal flaring
  • Intercostal and/or subcostal retraction.
• Prodrome usually lasting 1-3 days
• Total illness course is usually completed over 28 days

Radiographic features are also discussed in the literature, and they consist of hyperinflation and peribronchial thickening. Classically, there shouldn't be consolidation. Classically, there should also be no chest Xray, as the AAP recommends against it.

Features suggestive of severe bronchiolitis

Question 11 from the first paper of 2016 asked for four such features. The college listed a total of seven - eight if you include tachypnoea. They were as follows:

• Tachypnoea (over 70)
• Nasal flaring
• Grunting
• Subcostal or intercostal recession
• Tracheal tug ("suprasternal resession")
• Use of accessory muscles
• Apnoeic episodes
• Hypoxia on pulse oximetry (less than 90%)

Unsurprisingly, there are more formal way of looking at the severity of bronchiolitis. For example, in the study by Plint et al (2009) observers used the Respiratory Distress Assessment Instrument (RDAI) which was developed by Lowell et al in 1987 to measure the effects of nebulised adrenaline on bronchiolitic infants. Unfortunately all these tools are completely useless because the level of respiratory distress in infants varies from minute to minute (depending on the frequency and efficacy of hugs, etc) and so any given RDAI value becomes completely useless almost as soon as it is recorded.

Risk factors for severe bronchiolitis

The following list is a mixture of the Question 11 from the first paper of 2016, UpToDate and the AAP guideline.

• Ex prematurity
• Low birth weight
• Less than 12 weeks old
• Bronchopulmonary dysplasia of ex-prematurity
• Anatomical defects of the upper airways
• Hemodynamically significant congenital heart disease
• Immunodeficiency
• Neurological disease
• Smokers in the household
• Crowded households
• Attending day-care
• Older siblings
• Concurrent birth siblings
• High altitude 

Possible complications of bronchiolitis

• Aspiration pneumonia
• Apnoea
• Dehydration (too short of breath to feed)
• Respiratory failure requiring mechanical ventilation
• Bacterial superinfection

Assessment of bronchiolitis

This section is constructed in a manner which also answers the "assessment" components of  Question 6  from the first paper of 2009 and Question 28 from the first paper of 2008.

History

• Background (looking for the risk factors of severe bronchiolitis)
• Duration of illness (normal course is 7-10 days, should completely resolve within 1 month)
• History of complications
• Feeding history (i.e. adequate oral intake)
• Episodes of restlessness or lethargy
• History of unusual, severe or prolonged course (makes you think of congenital heart disease or some sort of defect in the immune system)

Examination

• Clinical features consistent with bronchiolitis
• Clinical features of severity
• Assessment for the need for intubation or NIV
• Clinically may also have mayconjunctivitis, pharyngitis, or acute otitis media

Investigations

• PCR for RSV, usually from nasal swabs
• Bloods will have a low yield
• CXR has no role to play unless you strongly suspect foreign body aspiration

Management of bronchiolitis

The management section here will discuss "ICUable" bronchiolitis, rather than the mild disease which is managed with "continue feeding, comfort" (the college model answer from Question 11 from the first paper of 2016). Severe bronchiolitis management can be described in the followign manner:

• Airway: ​ 
  • Assess the need for intuibation (rarely required)
  • Nasal suctioning to clear upper airway (not deep nasopharyngeal, but rather shallow nasal suctioning)
  •  
• Ventilation:
  • Just oxygen to begin with
  • Aim for sats of over 90%
  • CPAP or HFNP may be the next step of escalation. With infants, maximum flow rate is about L/min. 
  • Invasive mechanical ventilation may be required, but HFNP frequently prevents the need for this.
  • Respiratory distress will escalate whenever the child is handled; the key to respiratory success is to minimise handling and to group all routine cares so that the child gets long breaks between distressing events.
  • Apnoeas may be helped by caffeine or aminophylline
• Advanced strategies to improve gas exchange
  • ​Nebulised hypertonic saline 
  • Nebulised surfactant
  • Heliox
  • ECMO
  • None of these are strongly based in any sociaety recommendations, and sucess is mainly known from case reports
• Circulation:
  • ​IV maintenance fluids and resuscitation of dehydration
  • Assessment for any coexisting cardiac disease with TTE
• Electrolytes
  • Watch for SIADH: apparently that is one of the possible complications
• Nutrition
  • ​Nasogastric feeding to make up for recent deficit
• Antibiotics
  • ​Routine use of IV antibiotics is not indicated
  • Ribavirin has been trialled, and is also not recommended for routine treatment of RSV
    infection but may be considered in select immunocompromised individuals
  • Palivizumab, a humanized monoclonal antibody (IgG) directed against RSV, may be used in at-risk populations for prevention (eg. premature infants during RSV season).
• Strategies which have been trialled and which clearly do not work:
  • ​Nebulised bronchodilators
  • Montelucast
  • Corticosteroids (no evidence of benefit, and may even increase the duration of viral shedding)
  • Chest physiotherapy (probably no benefit)
  • Caffeine or aminophylline (they were supposed to decrease the risk of apnoeas, but they do not seem to work)
  • However, it must be mentioned that the trials of all these interventions excluded the "severe" category of patients.