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Systemic perfusion can be reduced by a wide variety
of processes and diseases that affect the infant and child. If the
poor perfusion is not promptly recognized and appropriate intervention
taken, there can be rapid progression to circulatory shock, a life-threatening
state. While the regulatory mechanisms that control circulatory
function are similar at all ages, some developmental features render
the infant and young child vulnerable to shock: (1) the infant’s
high surface-to-mass ratio causes excessively high insensible water
loss when there is fever, hypermetabolism, or a dry environment; (2)
the lack of free access to fluids limits the infant’s ability
to restore a fluid-volume deficit; (3) the exposure to certain pathogens
and susceptibility to overwhelming infection predispose the young
infant to septicemia; and (4) the perinatal closure of the ductus
arteriosus can precipitate a severely reduced systemic perfusion
in the presence of aortic stenosis or coarctation. The clinician
who examines the child with poor perfusion must thoroughly, rigorously,
and quickly assess the extent of the impairment to determine the
most likely mechanism(s) contributing to the circulatory disturbance
and to initiate therapy to restore circulation.
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Reduced systemic perfusion provokes some physical
manifestations that are nonspecific and some that reveal valuable
information about the cause of the particular disturbance. Any of
these signs should serve as a prompt for medical attention. Nonspecific
signs (eg, lassitude, hypotension, delayed capillary refill, pallor)
provide information about the severity of the dysfunction but are
not unique to a specific circulatory disturbance. Other, more specific signs
(eg, crackles, gallop rhythm, peripheral edema, and hepatosplenomegaly)
are not found in all patients, because they result from the physiological
alterations produced by particular circulatory disturbances; these
often provide valuable clues about the cause or mechanism of the
derangement.
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In considering both nonspecific and specific
manifestations, it is useful to start by clarifying some terms. Impaired
perfusion describes any state in which blood flow to the tissues
is appreciably decreased. It encompasses a wide range of problems,
from mild decreases in the circulating blood volume to cardiovascular
collapse. Shock is the extreme form of impaired
perfusion in which systemic blood flow is insufficient to sustain
vital functions. An essential component of shock is that it is an
unstable state; if left untreated, and possibly even if treated,
it causes progressive dysfunction of multiple organs, signs of severe
tissue ischemia (eg, lactic acidemia), and death. Congestive
heart or circulatory failure (see Chapter 497) is another form of impaired perfusion
in which the compensatory mechanisms of the cardiovascular system
maintain vital functions but cause the patient to suffer complications
from the adaptations (eg, peripheral and pulmonary edema, azotemia). Congestive
circulatory failure is a more stable state than shock.
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Understanding how disease can alter the normal
mechanisms that maintain and regulate tissue perfusion greatly facilitates
assessing the child with impaired systemic blood flow.
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Blood flow and the supply of nutrients are normally in great
excess of metabolic demands. ...