Bronchiolitis

Bronchiolitis

Summary

Description

·         Viral inflammation of the bronchioles usually seen in young children and occasionally in high-risk adults

·         The most common serious respiratory infection in infancy

·         Seasonal occurrence often in epidemics

·         May lead to respiratory distress requiring in-hospital care

·         Treatment is largely supportive

·         Respiratory syncytial virus (RSV) is the pathogen in 70% to 80% of cases

Synonyms

Capillary pneumonia.

Immediate action

·         Assess for signs of respiratory distress and admit if baby is tired or compromised

·         Recognize risk factors for severe disease, including severe prematurity, bronchopulmonary dysplasia, and congenital heart disease

·         Look for intercostal retraction, pyrexia, and tachypnea, which predict need for hospital care

·         Tired babies who are unable to maintain fluid balance or feed adequately require hospital assessment

·         The higher the respiratory rate, the lower the arterial oxygen tension

·         Hypercapnia does not usually occur until respirations exceed 60 breaths/minute; it then increases in proportion to the tachypnea

·         Consider admission in young infants if respirations exceed 60 breaths/minute, as feeding is likely to be severely compromised

·         Signs of severe, life-threatening illness are central cyanosis, tachypnea of more than 70 breaths/minute, listlessness, and apneic spells

·         At this stage, the chest may be greatly hyperexpanded and almost silent to auscultation because of poor air exchange

Urgent action

·         Assess respiratory effort and hydration status

·         Assess parental level of concern about the severity of child's illness, and ability to care for the child

Key points

·         Bronchiolitis is a viral, self-limited respiratory illness that resolves without long-term complications in most previously well children

·         The management of bronchiolitis is largely supportive; few medical therapies have demonstrated effectiveness in reducing clinical symptoms and hospitalizations

·         The single most effective means of preventing nosocomial spread of RSV bronchiolitis is hand decontamination with alcohol hand rubs or soap and water washes prior to and after each patient contact

Background

Cardinal features

Pathology:

·         Virus-induced inflammation of the bronchiolar epithelium, with hypersecretion of mucus and edema of the surrounding submucosa

·         These changes result in formation of mucous plugs obstructing bronchioles with consequent hyperinflation or collapse of the distal lung tissue

·         Infants are particularly apt to experience small airway obstruction because of the small size of the normal bronchioles; even minor thickening of the bronchiolar wall in infants may profoundly affect airflow

·         Resistance in small air passages is increased during inspiration and expiration, but because airway radius is smaller during expiration, resultant ball valve respiratory obstruction leads to early air trapping and overinflation

·         Atelectasis may occur when obstruction becomes complete and trapped air is absorbed

Presentation:

·         Most affected infants have history of exposure to older children or adults with minor respiratory diseases within the week preceding onset of illness

·         Mild upper respiratory tract infection with serous nasal discharge and sneezing usually precedes

·         These symptoms usually last several days and may be accompanied by diminished appetite and fever of 101 to 102ºF (38.5-39ºC)

·         Gradual development of respiratory distress is characterized by paroxysmal wheezy cough, dyspnea, tachypnea, and irritability

·         In mild cases, symptoms disappear in 1 to 3 days

·         In more severely affected patients, symptoms may develop within several hours, and the course is protracted

·         Breast- or bottle-feeding may be difficult because the rapid respiratory rate may not permit time for sucking and swallowing

·         Other systemic manifestations, such as vomiting and diarrhea, are usually absent

·         Hypoxemia is frequent and tends to be more marked than anticipated on the basis of the clinical findings. When severe, it is frequently accompanied by hypercapnia and acidosis

·         Second and third severe attacks are uncommon, although infection does not grant long-term immunity

Causes

Common causes

·         Respiratory syncytial virus (RSV) (70% to 80%)

·         Parainfluenza

·         Adenovirus

·         Human metapneumovirus

·         Rhinovirus (tends to cause upper respiratory tract illness more than lower)

·         Influenza virus

·         Chlamydial pneumonia

·         Source of viral infection is usually a family member with minor respiratory illness

·         Older children and adults tolerate bronchiolar edema better than infants and do not acquire the clinical picture of bronchiolitis, even when the smaller airways of the respiratory tract are infected

RSV:

·         Medium-sized, membrane-bound, RNA paramyxovirus

·         Incubation period from exposure to first symptoms is about 4 days

·         Virus is excreted for variable periods, probably depending on severity of illness and immunologic status

·         Most infants with lower respiratory tract illness shed virus for 5 to 12 days after hospital admission

·         Excretion for 3 weeks and longer has been documented

·         Spread of infection occurs when large, infected droplets, either airborne or conveyed on hands, are inoculated in the nose or conjunctiva of a susceptible subject

·         RSV is probably introduced into most families by schoolchildren undergoing reinfection

·         Nosocomial infection during RSV epidemics is an important concern. Virus is usually spread from child to child on the hands of caregivers

·         Adults undergoing reinfection have also been implicated in spread of the virus

Serious causes

Adenoviral bronchiolitis may be associated with a higher incidence of complications, including need for hospital admission and for supplemental oxygen.

Contributory or predisposing factors

·         Contact with infected person

·         Children in daycare environment

·         Heart-lung transplantation patient

·         Children with bronchopulmonary dysplasia

·         Adults: exposure to toxic fumes, connective tissue disease, immunocompromised state

·         Diminished lung function may play a role in determining which infants with viral infection acquire bronchiolitis

·         Infants whose mothers smoke cigarettes are more likely to get bronchiolitis than are infants of nonsmoking mothers

·         Despite risks of respiratory infections in children who attend childcare, bronchiolitis is more likely in infants who stay at home with mothers who are heavy smokers than in infants who attend daycare centers

·         Premature infants, especially those born at <30 to 32 weeks' gestation, and those with chronic lung disease, such as bronchopulmonary dysplasia, are at greatest risk for severe episodes of RSV-linked disease

·         Infants with congenital heart disease also are more prone to severe RSV-related illness

Epidemiology

Incidence and prevalence

Incidence

·         The incidence is highest during the winter and early spring

·         Medical care is provided to 1000 to 1500/100,000 annually in U.S.; estimated incidence is higher

·         In the U.S. and Britain, 1% to 3% of infants with bronchiolitis are admitted to hospital with the condition each winter

·         Of those admitted, about 2% to 5% will require mechanical ventilation; this is more likely in premature babies and babies with existing lung disease. The mortality rate is <1% for all infants overall, but ranges from 3% to 10% for infants with chronic lung disease or congential heart disease

Prevalence

·         It is estimated that in an urban setting about half of the susceptible infants undergo primary infection in each epidemic; virtually all are symptomatic

·         More than 90% of children are infected with RSV in the first 2 years of life

Demographics

Age

·         Newborn to 2 years (peak age 2-6 months), though can occur in adults

·         Placentally transmitted anti-RSV antibody has some protective effect

·         This may account for the low frequency of severe infections during the first 4 to 6 weeks of life, except in infants born prematurely

·         Serum antibody is not fully protective, and the age at which an infant undergoes first infection depends also on the opportunities for exposure

Gender

·         1:1 male to female as outpatients

·         2:1 male to female in hospital

Geography

·         RSV is distributed worldwide and appears in yearly epidemics

·         In temperate climates, these epidemics occur each winter and last 4 to 5 months

·         During the remainder of the year, infections are sporadic and uncommon

·         In the northern hemisphere, epidemics usually peak in January, February, or March, but peaks have been recognized as early as December and as late as June. At these times, hospital admissions for bronchiolitis and pneumonia of children younger than 1 year increase and decrease in proportion to the number of RSV infections in the community

·         In the tropics, the epidemic pattern is less clear

Socioeconomic status

·         Bronchiolitis occurs most commonly in male infants between 3 and 6 months of age who have not been breast-fed and who live in crowded conditions

·         Infants whose mothers smoke cigarettes are more likely to acquire bronchiolitis than are infants of nonsmoking mothers

·         Bronchiolitis is more likely to develop in infants who stay at home with mothers who are heavy smokers than in infants who attend daycare centers

·         Lower respiratory tract involvement occurs more often and earlier in life in lower socioeconomic groups and in crowded living conditions

·         American Indians and native Alaskans have high incidences of bronchiolitis