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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.
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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.
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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.
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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 ...