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Shock is a clinical condition that occurs when there is inadequate delivery of oxygen and other nutrients to meet the metabolic demands of the tissues. If left untreated, shock results in irreversible cell and organ damage and death. The clinician must be able to recognize shock early, initiate therapy rapidly, and arrange safe transport of the patient to an intensive care facility. These lifesaving tasks require that the clinician have a fundamental knowledge of the causes, presentations, therapies, and complications of shock.
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Physiologically, shock can be classified as compensated, when the patient is able to maintain a normal blood pressure for age, or decompensated, when deterioration has led to hypotension. In general, compensated shock progresses to decompensated shock if left untreated, which emphasizes the importance of early recognition and intervention. Children can generally maintain a normal blood pressure until advanced stages of shock; therefore hypotension (see Table 36-1 for age-based definitions of hypotension) in a pediatric patient is an ominous sign of impending circulatory collapse. When measuring blood pressure with a sphygmomanometer, it is important to select the smallest cuff that covers two-thirds of the upper arm or leg.
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PATHOPHYSIOLOGY AND DEFINITIONS
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Shock can also be classified by cause, with the main types being hypovolemic, cardiogenic, and distributive shock, which includes septic shock. The mechanisms may differ, but inadequate tissue perfusion is the common final pathway.
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Hypovolemic shock, by far the most common type of shock in children, occurs when a decrease in intravascular volume leads to decreased venous return and subsequently, decreased preload. Decreased preload results in decreased stroke volume. An increase in heart rate often maintains cardiac output initially, but when this compensatory response is inadequate, cardiac output diminishes. The formula that defines this relationship is as follows:
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Cardiac output = Heart rate × Stroke volume
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Decreased cardiac output results in decreased delivery of oxygen and other substrates to the tissues. The two main categories of hypovolemic shock are hemorrhagic and non-hemorrhagic; examples are provided in Table 36-2.
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In the early stage of hypovolemic shock, autoregulatory mechanisms shunt blood flow preferentially to the brain, heart, and adrenal system thus preserving blood ...