Clinical Guidelines on the Management of Acute Bronchiolitis
Explanatory Notes on Level of Evidence and Grading System on Recommendation
The definition of types of evidence and grading recommendations originate from the US Agency for Health Care Policy and Research (AHCPR) and are also recommended and used by the Royal College of Paediatrics and Child Health.
Evidence is graded upon the methodological qualities. Guidelines normally contain many different recommendation based upon different levels of evidence. It is important that users are aware of the level of evidence on which each guideline recommendation is based. The link between guideline recommendation and the supporting evidence should be made explicit. Separating the strength of the recommendation from the level of evidence helps in situations where extrapolation is required to take the evidence of a methodologically strong study and apply it to the target population. Gradings of recommendation in addition to level of evidence allow more flexibility for future revision. However, it is important to emphasis that the grading does not relate to the importance of the recommendation.
Acute bronchiolitis is one of the most common lower respiratory infections suffered by infants. Studies have shown the local epidemiology is very much similar to that of the rest of the world. The present guideline aims to summarise the current evidence on the diagnosis and treatment of the condition, resulting in recommendations that are practicable both in the office and the hospital.
Definition of Bronchiolitis for This Guideline1
A. Age of 24 months or less
B. Expiratory wheezing of acute onset
C. Signs of viral respiratory illness such as coryza, otitis media, or fever
A review of the case definitions and inclusion criteria used in epidemiological studies and clinical trials revealed that many studies simply stated that infants with signs and symptoms consistent with bronchiolitis were eligible for inclusion. In others with more details, 43 trials used tachypnoea in the case definition or inclusion criteria; 42 used wheezing; 37 used oxygen saturation; and 32 used retractions.1 Notable differences of diagnostic criteria for bronchiolitis do exist among different studies. In America for example the term bronchiolitis seems to include a much wider range of illnesses. The North Carolina group whose epidemiological studies have been widely cited defined bronchiolitis as expiratory wheezing with or without tachypnoea, air trapping, and substernal retractions.2 The Rochester group had more restrictive diagnostic criteria: 1) expiratory wheezing of acute onset, 2) an age of 24 months or less, 3) signs of viral respiratory illness such as coryza, otitis media, or fever, 4) the first such episode, and 5) the presence or absence of indications of respiratory distress, pneumonia, or atopy.3 In U.K. or Australia the definition of bronchiolitis is generally even more restrictive. Studies of bronchiolitis have usually included only babies less than one year or 9 months.4,5 Some included only babies who had fine crepitations on physical examination.5
It is important to note that eligibility criteria in the clinical trials varied, especially with respect to criteria such as age, duration of symptoms, co-morbidities (e.g. prematurity and chronic lung disease), history of previous wheezing, and severity of disease. Specific study objectives determined most of these variations (e.g. some studies included only infants with first episode of wheeze with proven RSV infection, others included children with recurrent wheezing associated with any respiratory infection). Special attention should be given to the differential diagnoses between asthma and acute bronchiolitis during the appraisal of therapeutic trials, especially in infants, as the two conditions may bear many similarities in their presentation.
Aetiology and Epidemiology
As in Western countries, respiratory syncytial virus (RSV) is the commonest cause of acute bronchiolitis in Hong Kong. Other aetiological agents include parainfluenza and influenza viruses, adenoviruses, and mycoplasma pneumoniae. There are seasonal variations of incidence with a peak in the summer months, contrasting with winter outbreaks in Western countries.6
Clinical Features and Diagnosis3,7-10 (Level of evidence IV)
Diagnosis is based on clinical features:
Factors Associated with Severe Disease14-23 (Level of evidence III)
Indications for Hospital Admission13 (Level of evidence IV)
Indications for Admission to Paediatric Intensive Care Unit (PICU) 24 (Level of evidence IV)
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