Bronchiolitis Workup

Updated: Mar 25, 2018
  • Author: Nizar F Maraqa, MD, FAAP; Chief Editor: Russell W Steele, MD  more...
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Workup

Approach Considerations

The diagnosis of bronchiolitis is based on clinical presentation, the patient’s age, seasonal occurrence, and findings from the physical examination. When all of these are consistent with the expected diagnosis of bronchiolitis, few laboratory studies are necessary. [3] Tests are typically used to exclude other diagnoses (eg, bacterial pneumonia, sepsis, or congestive heart failure) or to confirm a viral etiology and determine required infection control for patients admitted to the hospital. Severely ill children may have dual viral infections.

Although the use of diagnostic tests is common, several investigators argue that these should not be routinely performed, citing concerns about costs, inappropriate use of antibiotics, unnecessary hospitalization, and the lack of proven benefit. In reality, few studies have rigorously evaluated the utility of diagnostic tests for this disease. Some hospitals have developed their own protocols or guidelines for testing and management, whereas others have left the decision entirely to the treating physician.

According to a survey of hospital-based pediatricians, the most common tests are rapid viral antigen testing of nasopharyngeal secretions for respiratory syncytial virus (RSV), arterial blood gas (ABG) analysis (in severely ill patients, especially those requiring mechanical ventilation), white blood cell (WBC) count with differential, C-reactive protein (CRP) level, and chest radiography.

Other common tests are pulse oximetry, blood culture, urine analysis and culture, and cerebrospinal fluid (CSF) analysis and culture. Urine specific gravity may provide useful information regarding fluid balance and possible dehydration. Serum chemistries are not affected directly by the infection but may aid in gauging severity of dehydration.

In previously healthy children with viral bronchiolitis, chest radiography, complete blood count (CBC), or blood culture are usually unnecessary. However, these tests should be carefully considered in persons with severe disease or a very ill appearance, preexisting cardiac or pulmonary disease, a markedly elevated temperature, or other risk factors for more severe disease. A few children at risk for acute respiratory failure may require monitoring of the blood carbon dioxide level.

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WBC Count and Differential

The WBC count is usually 8,000-15,000/µL and may be left-shifted as a result of stress. Although the WBC count with differential is commonly performed to look for coexisting bacterial infection, few studies have evaluated its utility for this purpose. Elevated WBC counts do not predict serious bacterial infection in children hospitalized with RSV bronchiolitis. [84] However, case reports have described patients with bronchiolitis who had elevated WBC counts that prompted further evaluation and eventual identification of a bacterial pathogen.

In a study of 120 infants with RSV infection, Saijo et al [108] demonstrated a correlation between an elevated WBC count and a radiographic pattern of lobar pneumonia as compared with a pattern of bronchopneumonia or bronchiolitis. CRP levels and erythrocyte sedimentation rate (ESR) followed the same pattern in this study. Veira et al [109] also observed an association between a viral etiology and low WBC counts and CRP levels during initial and follow-up testing.

The WBC count has been decried for its poor test characteristics. Among infants with a febrile illness, WBC values are highly variable. No WBC count threshold has good discriminatory value for the presence of bacterial infection. WBC testing should not be routinely performed in patients with bronchiolitis. [110]

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Sepsis Workup

In most patients with RSV bronchiolitis, especially those with mild disease, the risk of serious secondary bacterial infection is low. Kuppermann et al [83] found no evidence of bacteremia in 156 patients with bronchiolitis aged younger than 24 months; patients with lobar consolidation were excluded. Liebelt et al [111] studied infants aged 90 days or younger with bronchiolitis and noted a low risk of serious bacterial infection and wide variability in the use of diagnostic tests in this population.

Multivariate analysis identifies temperature greater than 38°C, oxygen saturation less than 92% at presentation, and a history of apnea as clinical predictors of the use of laboratory studies.

Antonow et al [112] studied 282 hospitalized infants younger than 60 days with bronchiolitis and reported a low rate of serious bacterial infections (5 of 140 tested). A multivariate model identified a higher bronchiolitis score and normal chest radiograph findings as positive predictors of a sepsis workup, whereas an admission diagnosis of bronchiolitis and a chest radiograph with findings typical for bronchiolitis were negative predictors.

Among 1795 children aged 0-14 years who were hospitalized for RSV bronchiolitis, Bloomfield et al [113] reported positive blood culture findings in 11 of 861 children tested. Risk factors for concurrent bacteremia included nosocomial RSV infection, cyanotic congenital heart disease, and admission to the pediatric intensive care unit (PICU). The authors recommended considering antibiotic therapy for children with severe RSV bronchiolitis admitted to the PICU, particularly if needing mechanical ventilation.

In a prospective multicenter study aimed at determining whether infants younger than 60 days with fever and bronchiolitis are at increased risk of serious bacterial infection, 269 (22%) of the 1248 patients enrolled had RSV bronchiolitis. The rate of secondary bacterial infections was 7% in the RSV-positive group and 12.5% in the RSV-negative group. The rate of secondary bacterial infections in the RSV-positive group was smaller but remained appreciable.

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Viral Testing

When viral testing is performed, RSV is the most commonly isolated organism (26-95%). Such testing is frequently performed in febrile young children who present to the emergency department (ED) with bronchiolitis. It has been argued that rapid identification of a viral cause of a febrile illness obviates the need for a sepsis workup or empiric use of antibiotics, particularly in children who were previously well or do not appear toxic.

Although viral culture for RSV is available and must be considered the standard for making a definitive diagnosis, several commercially available immunologic and molecular-based tests are more rapid, and convenient. The antigen detection tests identify the RSV antigen in epithelial cells from nasopharyngeal secretions, bronchoalveolar lavage fluid, or lung tissue using either direct immunofluorescent antibody (IFA) staining or an enzyme-linked immunosorbent assay (ELISA). The reliability of the tests is highly dependent on sampling techniques. [114] The antigen is attached to mucosal epithelial cells. Simply sampling the mucus from a nasal swab is clearly less traumatic but not nearly as reliable as a swab of the nasopharyngeal area or, preferably, a nasal washing. One third of nasal swab sample results are negative compared with results obtained with more aggressive techniques. With adequate sampling, IFA staining requires 2-6 hours for processing and is 90% sensitive and specific. On the other hand, ELISA requires 30 minutes for processing and is 85-90% sensitive as compared with viral culture. Although ELISA is somewhat quicker and easier to interpret because it yields a more objective endpoint, the IFA technique may be preferable, in that it permits determination of the number of epithelial cells recovered and thereby can verify the adequacy of the sample.

The reliability of rapid antigen detection tests in adults is questionable. [115, 116] RSV samples from adult patients showed 14-39% sensitivity when compared with culture. The decreased performance of rapid test kits with adult samples may be due to numerous factors, including a shorter shedding phase, lower viral titers, and dry mucosa.

Newly available molecular tools such as polymerase chain reaction (PCR) techniques are more commonly being used in diagnosis and epidemiologic surveillance of RSV and other viral infectious agents in infants hospitalized for bronchiolitis. These tests are more sensitive than other diagnostic approaches and now form the backbone of clinical virology laboratory testing. Use of multiplex PCR assays may allow rapid and accurate identification of common and uncommon viral respiratory pathogens. [117]

Although viral detection is commonly practiced and may have good utility, routine testing is not recommended in infants with bronchiolitis. [110] An argument can be made that it has little influence on outcome, however, RSV testing does influence management in that physicians appear to be more likely to withhold antibiotics or to stop them sooner in patients who test RSV-positive. Additionally, despite the fact that infection control procedures are similar for most respiratory viruses, viral testing may be used to isolate hospitalized patients who test positive and to categorize patients for cohort nursing.

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Pulse Oximetry

Transcutaneous oxygen saturation is reduced in cases of moderate to severe bronchiolitis. However, it is a poor predictor of respiratory distress. It correlates best with tachypnea, but correlates poorly with wheezing and retractions. Patients with persistent resting oxygen saturations below 90% in room air require a period of observation and possible hospitalization. Because of atelectasis, administration of beta-agonist aerosol may increase the heart rate and thus cardiac output without improving ventilation, causing relative desaturation (ie, ventilation-perfusion mismatch).

Recent management guidelines have suggested lower limits of acceptable oxygen saturation levels of 90% for infants with bronchiolitis. The use of pulse oximetry monitoring is not recommended routinely in infants with bronchiolitis who do not require supplemental oxygen or have oxygen saturation >90% on room air. [110, 118]

Increased reliance on the oxygen saturation level may have contributed to the substantial increase (nearly 250%) in the hospitalization rate for children with bronchiolitis since the 1980s. [119, 118] There is some evidence that for previously healthy children admitted with bronchiolitis, hospital discharge may be delayed because of pulse oximetry values when the patients are otherwise stable for discharge, thereby potentially contributing to increased costs. The implications of a particular oxygen saturation level may vary, depending on whether the level is determined upon admission in a child who is sick or upon discharge in a child who is otherwise stable.

A study to determine the effect of intermittent vs continuous pulse oximetry monitoring on hospital length of stay among nonhypoxemic infants and young children hospitalized for bronchiolitis concluded that intermittent pulse oximetry monitoring did not shorten hospital length of stay and was not associated with any difference in rate of escalation of care or use of diagnostic or therapeutic measures. These results suggest that intermittent pulse oximetry monitoring can be routinely considered in the management of infants and children hospitalized for bronchiolitis who show clinical improvement. [120, 121] According to a prospective cohort by Principi et al, pulse oximetry does not effectively predict which infants diagnosed with bronchiolitis will return for unscheduled medical care after an emergency department discharge. [122, 123]

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Chest Radiography

Chest radiographs are not routinely necessary. [4] If clinically indicated, they should include anteroposterior (AP) and lateral views. Chest radiography is most useful in excluding unexpected congenital anomalies or other conditions [5, 6] ; it may also yield positive evidence of alternative diagnoses (eg, lobar pneumonia, congestive heart failure, or foreign body aspiration). Confine neck radiography or contrast studies to children whose diagnosis is unclear or who have histories consistent with structural anomalies.

Findings from chest radiography in individuals with bronchiolitis are variable. Hyperinflation is usually present (see the image below), and 20-30% of chest radiographs show lobar infiltrates, atelectasis, or both. [124] Atelectasis is common and contributes to arterial desaturation. Because ciliated bronchial epithelium does not regenerate for 9-15 days, atelectasis may be persistent and shifting.

A chest radiography revealing lung hyperinflation A chest radiography revealing lung hyperinflation with a flattened diaphragm and bilateral atelectasis in the right apical and left basal regions in a 16-day-old infant with severe bronchiolitis. Image courtesy of Wikipedia Commons.

Other findings may include bronchial wall thickening, air trapping, flattened diaphragm, increased AP diameter, peribronchial cuffing, tiny nodules, linear opacities, and patchy alveolar opacities. Opacities on radiographs do not suggest bacterial pneumonia and incorrectly lead to inappropriate treatment with antibiotics.

In one study, only 2 of 265 infants were found to have radiographic findings inconsistent with simple bronchiolitis; the risk of airspace disease was particularly low in children with saturation higher than 92% and mild-to-moderate respiratory distress. [125]

In a study of 153 children with acute bronchiolitis, Dawson et al [124] found no correlation between the degree of change on the chest radiograph and a clinical scoring method. However, in Shaw’s study [38] of 213 infants with bronchiolitis, atelectasis was 2.7 times more likely to be found at presentation in the patients with severe disease than in those with mild disease.

Although negative findings from chest radiograph may have some value, children who do not appear ill are unlikely to have a radiograph that shows abnormalities. A practical approach is to obtain a chest radiograph in children who appear ill, are experiencing clinical deterioration, or are at high risk (eg, those with underlying cardiac or pulmonary disease).

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Other Studies

Electrocardiography (ECG) or echocardiography should be reserved for those few children who display arrhythmias or cardiomegaly.

In rare situations, such as severe immunodeficiency or a strong history of possible foreign body aspiration, bronchoscopy may be indicated for diagnostic bronchoalveolar lavage or therapeutic foreign body removal.

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