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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.

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.

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.

Understanding how disease can alter the normal mechanisms that maintain and regulate tissue perfusion greatly facilitates assessing the child with impaired systemic blood flow.

Blood flow and the supply of nutrients are normally in great excess of metabolic demands. ...

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