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Respiratory illness in children usually presents with clinical symptoms and signs that offer important information for further diagnostic tests. The primary function of the respiratory system is to provide a supply of oxygen and removal of carbon dioxide, that is, adequate and adaptive gas exchange. Illness can disturb this function by affecting respiratory control, the respiratory pump, that is, chest cage and respiratory muscles, airways, and the pulmonary tissues. The many nonrespiratory functions of the lung include production and regulation of surfactant, defense against infections, participation in water and fluid balance, sieving of blood cells and emboli, and elimination of volatile substances. The clinical presentation of illness interfering with these functions is often related to the secondary effects on respiratory mechanics and gas exchange.

Efforts to formalize the assessment of clinical signs in respiratory illness for estimation of disease severity have resulted in numerous clinical scores, for example, for croup,1 bronchiolitis and pneumonia,2 and for asthma.3,4 Clinical signs as the basis of these scores include tachypnea, visibly increased respiratory effort, for example, retractions and use of accessory muscles, reduced breath sound intensity (often referred to as “air entry”), wheezing, relative duration of expiration, cyanosis, and mental status.

The number of breaths per minute is counted by observing chest and abdominal movements or by listening to breaths with a stethoscope. Respiratory rates established by auscultation may be slightly higher than those by observation, particularly when placement of the stethoscope on the chest stimulates the child. Children have higher respiratory rates during wakefulness than during sleep. The range of respiratory rates in a healthy child is wide but narrows when a higher breathing rate is maintained during respiratory illness. Breathing rates are related to age and weight, showing an exponential decrease with increasing age and body mass. Age specific normative data have been established for infants and toddlers5 and for older children6 (Fig. 505-1). Fever and respiratory disease can increase the respiratory rate. In young febrile children tachypnea, that is, a respiratory rate faster than normal, is an important predictive sign for pneumonia when the respiratory rate per minute exceeds 59 in those under 6 months of age, 52 between 6 and 11 months, and 42 between 1 and 2 years.7 Observer agreement on tachypnea is generally good.

Figure 505-1.

Normal range of respiratory rates during wakefulness.

(Data from Rusconi FM, Castagneto L, Gagliardi G, et al. 1994. Reference values for respiratory rate in the first 3 years of life. Pediatrics. 1994;94:350-355. Wallis LA, Healy M, Undy MB, Maconochie I. Age related reference ranges for respiration rate and heart rate from 4 to 16 years. Arch Dis Child. 2005;90:1117-1121.)

Increased resistance to airflow can lead to inspiratory retractions of the more compliant parts of the chest. These are most easily visible in young children because of their ...

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