Summary

Acute bronchiolitis is the commonest cause of lower respiratory tract infection in infants and young children. Respiratory syncytial virus (RSV) is the etiological agent in most cases of acute bronchiolitis. Clinical features of acute bronchiolitis include tachypnoea, inspiratory crackles and expiratory wheeze. High fever is unusual. Treatment of acute bronchiolitis includes oxygen and intravenous fluid in case of poor feeding. In the presence of expiratory wheeze, treatment with nebulised salbutamol, ipratropium bromide or adrenaline may be tried. Efficacy of these agents must be established for individual patients as response varies with different individuals. Post-bronchiolitis wheeze and asthma is very common. Avoidance of cigarette smoke must be stressed. Preliminary data suggested beneficial effects of inhaled corticosteroid in preventing recurrent wheeze or asthma in children with RSV bronchiolitis.

摘要

急性細支氣管炎是嬰幼兒下呼吸道感染最常見的 原因，絕大多數由呼吸性和胞病毒引起。臨床表現包括呼吸急促、吸氣性爆裂音和呼氣性喘鳴。高燒並不 常見。治療包括吸氧和進食不良時進行靜脈輸液。有呼氣性喘鳴音時，可使用霧化舒喘寧、異丙托溴胺或 腎上腺素。因病人對藥物的反應不同，藥效亦因人而異。細支氣管炎後喘鳴和哮喘極常見，必須強調避免 吸煙。初步的數據提示呼吸性合胞病毒性細支氣管炎的兒童吸入皮質類固醇，對預防復發性喘鳴和哮喘有 幫助。

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Introduction

Acute bronchiolitis is an acute viral respiratory tract infection affecting the small airways of young infants. Respiratory syncytial virus (RSV) accounts for 70-96% of cases.¹ Virtually 100% of young children are infected with RSV in the first few years of life, and about 66% of infants are infected during their first year.² Twelve³ to 40%⁴ of RSV-infected infants will develop lower respiratory tract infection, i.e. bronchiolitis or pneumonia.

Hong Kong epidemiology

From 1997 through 1999, 9,948 children were discharged from public hospitals in Hong Kong with a diagnosis of acute bronchiolitis.⁵ This data should reflect accurately the incidence of moderate to severe bronchiolitis in Hong Kong since public hospitals account for more than 90% of hospital beds in Hong Kong. For the same period, there were 196,919 paediatric discharges from public hospitals. Hence, acute bronchiolitis accounted for 5.05% of paediatric discharges in Hong Kong whilst acute bronchiolitis accounted for 3.12% of admissions for infants in USA in 1996.⁶ Acute bronchiolitis occurs significantly more often during the hot and humid months in Hong Kong from March to September, 1098 vs 557 discharges per month (p<0.01).

This is exactly opposite to that reported from USA where it peaks in mid-Winter.⁷

Clinical features

Acute bronchiolitis is basically a clinical diagnosis. It is usually preceded by a few days of rhinorrhoea, cough and low grade fever. Involvement of bronchioles is reflected by tachynpoea, flaring of alae nasi, suprasternal insucking, inspiratory crackles and expiratory wheeze. It is important to note that wheeze may not be present in acute bronchiolitis. Absence of high fever and percussion dullness would help differentiate acute bronchiolitis from may show hyperinflation, bronchial wall-edema and linear opacities in the perihilar area. Full blood counts and electrolytes are usually normal. Hypoxaemia may not be correlated with clinical severity of bronchiolitis.⁸ Arterial blood gases assessment should be done for severe cases for documentation of CO₂ retention. Advances in the rapid diagnosis of RSV, e.g. immunofluorence or enzyme-linked immunosorbant assays, allow accurate early identification.

Treatment of acute bronchiolitis

Management includes humidified oxygen to keep pulse oximetry reading above 95% and appropriate nutrition support. The use of bronchodilators in the treatment of acute bronchiolitis is controversial. Nebulised salbutamol (0.15mg/kg/dose), ipratropium bromide (250 micrograms/dose) and epinephrine (3ml of 1:1000 epinephrine) have all been studied with conflicting results. Kellner etal⁹ performed a meta-analysis of use of bronchodilators, i.e. salbutamol, ipratropium and epinephrine, in bronchiolitis. He found that these bronchodilators produced modest short-term improvement with no effect on oxygenation, duration of hospitalisation and rate of hospitalisation. It is the authors' observation that both nebulised salbutamol and ipratropium bromide were widely used in treatment of acute bronchiolitis in Hong Kong whilst nebulised epinephrine was less frequently used.

Ribavirin is a synthetic nucleoside analogue with virostatic activity against RSV. It is given as small particle aerosol, 6 gram per day over 12 to 20 hours for 3-5 days. In 1996, the American Academy of Paediatrics (AAP) recommended that ribavirin may be considered in selected patients at high risk for serious RSV pneumonia or those with severe RSV infection.¹⁰ This represented a change in position from "should be used" as recommended by AAP in 1993 as increasing evidence for lack of benefit from ribavirin were reported. However, the authors found the use of ribavirin to coincide with clinical improvement in the handful of severe cases that were managed in our department.

The addition of oral steroids to nebulised salbutamol had no effect on length of admission, lung function or clinical recovery.¹¹ Nebulised budesonide was studied in the treatment of acute bronchiolitis but the result was disappointing.¹² Shuang Huang Lian, a Chinese herb, was reported to be effective in shortening duration of fever, wheeze, cough.¹³ Interferon alft-2a, 50,000 IU/kg/day, was studied in the treatment acute bronchiolitis with conflicting results.^14,15

Post-bronchiolitis airway hyper-responsiveness

After acute bronchiolitis, up to 50% of infants developed recurrent wheeze.⁷ In the only prospectively monitored case controlled series,^16,17 asthma was present in 23% of the RSV group and 1% of the control group (p>0.001) at the mean age of 3-year. During follow up studies at the mean age of 7.5 years, asthma was present in 30% of the RSV group versus 3% of the control group (p<0.0001). Both the RSV and control group were similar in terms of family history of atopy and asthma, current atopy status as determined by skin prick test and/or serum tests. In the same studies,^16,17 there was no significant difference in prevalence of asthma between those RSV-infected individuals with a family history of asthma and those RSV-infected individuals without a family history of asthma. Hence, RSV bronchiolitis in infancy is associated with an increased risk of future asthma. A family history of atopy and/or asthma does not explain this increased risk of asthma. Whether RSV per se can contribute to the development of asthma or merely unmask those who are genetically predisposed to asthma remains unclear.

"How do I prevent my child from developing asthma after RSV bronchiolitis?" is a common question for family practitioners. The evidence so far suggests avoidance of cigarette exposure and heavy house dust mite exposure. A diet rich in vitamin C, fish oil and low in sodium may be helpful.¹⁸ Inhaled steroids were studied in relation to prevention of recurrent wheeze after an episode of acute bronchiolitis. The duration of inhaled steroids varies from 2 weeks¹⁹ after discharge to 16 weeks.²⁰ Different forms of steroids were studied: oral,²¹ nebulised budesonide,²⁰ budesonide puff.²² In view of difference in treatment regime, it came as no surprise that the results differed among these studies. No difference was observed for amount of wheeze for those given oral prednisolone (1mg/kg/day) for 7 days.²¹ For those given inhaled budesonide for eight weeks or less, no difference was found between the treatment groups and placebo groups.^19,22,23 For those treated with inhaled budesonide for more than 8 weeks, i.e. 9 weeks²⁴ and 16 weeks,²⁰ beneficial effects were reported in the treatment group. Fewer episodes of wheeze were reported for the treatment group during the 16 weeks of treatment with 250mcg to 500mcg of nebulised budesonide twice a day.²⁰ For those treated with nebulised budesonide for 9 weeks, 500mcg bid, fewer children in the treatment group were put on asthma medications during two years of follow up.²⁴ It appeared that nebulised therapy with an inhaled corticosteroid may improve respiratory outcomes in the first few years after RSV bronchiolitis. Longer term studies are required.

Conclusion

In Hong Kong, the prevalence of acute bronchiolitis that required hospital admission was similar to that of USA. However, the RSV season was opposite to that of USA, i.e. summer in Hong Kong and winter in USA. In-patient treatment appeared to be similar to that in USA. There is little data about efficacy of various bronchodilators in the treatment of acute bronchiolitis in Hong Kong or in Chinese patients. Post-RSV bronchiolitis recurrent wheeze or asthma is a common problem that is not well documented in Hong Kong. Further studies into effective treatment of acute bronchiolitis and occurrence of asthma after RSV bronchiolitis are warranted in Hong Kong.

Key messages

1. Respiratory syncytial virus (RSV) is the commonest cause of acute bronchiolitis in infants and young children.
2. The RSV season is summer in Hong Kong in contrast to the winter peak in North America.
3. Clinical features of acute bronchiolitis includes tachypnoea, inspiratory crackles and expiratory wheeze.
4. In acute bronchiolitis, treatment of expiratory wheeze must be individualised as response to nebulised salbutamol, ipratropium bromide or adrenaline differs in different individuals.
5. Post-bronchiolitis recurrent wheeze is very common and use of nebulised corticosteroids may be beneficial.

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References