Clinical Features

Infection begins with nasal discharge, pharyngitis, and cough. Fever accompanies the first few days of illness, with temperatures as high as 40°C (104°F). The parent brings the child to the ED because of increased respiratory symptoms, nasal congestion, and difficulty feeding.

Symptoms reach a peak at 3 to 5 days, generally resolving in 2 weeks with normalization of pulmonary function. It must be noted that resultant wheezing can persist for weeks to months. Respiratory isolation precautions should be entertained owing to the severity of illness that can occur in children with a history of prematurity, cystic fibrosis, congenital heart disease, or immunocompromise. These latter children are more at risk for apnea also.

Physical findings include tachypnea greater than 50 to 60 breaths per minute, tachycardia, mild conjunctivitis, chest retractions, prolonged expiration with hyperresonant chest, wheezes throughout, and hypoxemia. The most reliable clinical finding that correlates with hypoxemia is tachypnea, which signifies serious impairment of gas exchange. The hypoxemic child with bronchiolitis may not show cyanosis. The severity of wheezing or intercostal retractions will also not correlate with the severity of hypoxemia. Respiratory rate must be followed, but this may be difficult, as variation occurs with fever and crying. Pulse oximetry is the single best objective predictor of severe disease, and most children with saturations of less than 91 percent will probably need admission. If respiratory rate cannot be determined in the very small or dehydrated child, an arterial oxygen saturation should be obtained.

YOUNG INFANTS AND APNEA The mechanism inducing RSV-related apnea in young infants is not completely understood but may be related to hypoxemia and upper airway obstruction.51 Infants at highest risk are less than 6 weeks old, have a history of prematurity, apnea of prematurity, and low O 2 saturation on admission. It is difficult to predict apneic events. The severity of wheezing and retractions does not correlate with frequency of apnea, and most infants less than 1 month of age will have atypical disease, where they may present without wheezing and retractions. Apneic infants generally require intubation during the course of the illness, sometimes requiring mechanical ventilation for up to a week or more. Postextubation, these infants are not at higher risk of apnea and may be discharged without apnea monitors.

Children with underlying diseases such as bronchopulmonary dysplasia, cystic fibrosis, immunodeficiency, or congenital heart defects are at increased risk of severe RSV. Care must be taken in treating infants with a history of BPD, as many will have a tendency toward chronic CO 2 retention. Since hypoxemia remains the major respiratory stimulus in this population, supplemental oxygen may cause further CO 2 retention, therefore saturations of 94 to 95 percent are acceptable.

Numerous retrospective analyses and observations note that children with bronchiolitis as infants frequently develop asthma later on. 52 Diagnosis

The diagnosis of bronchiolitis is suggested by clinical presentation, patient age, and history of RSV exposure or community epidemic. Immunofluorescence assays currently available are extremely sensitive but not necessary for all patients. Since the prevalence of RSV during an epidemic is so high, routine testing is costly and is best reserved for children with predisposing medical conditions or complicated courses of disease.

Complete blood counts (CBCs) and chemistries may not be helpful in diagnosis. The white blood cell count can be normal or elevated with a left shift. An elevated band count may be present. Chemistries should be obtained if there is poor feeding or evidence of dehydration. Salicylate ingestion may present with respiratory distress, and mixed metabolic acidoses and respiratory alkelosis and b-blocker ingestions can exacerbate wheezing, so the history should include questioning about possible injestion. Chest x-ray may reveal patchy atelectasis, segmental atelectasis, hyperinflation, and peribronchial thickening.

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