Shock

Published on 06/06/2015 by admin

Filed under Pediatrics

Last modified 06/06/2015

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2 Shock

Shock is an acute clinical syndrome of circulatory dysfunction in which there is failure to deliver sufficient oxygen and substrate to meet metabolic demand. All practitioners who care for children must understand and identify shock promptly to initiate an effective treatment plan. This, in turn, can help prevent the progression and poor outcomes that characterize the natural clinical course of shock. The goal is to prevent end-organ damage; failure of multiple organ systems; and, ultimately, death.

Etiology and Pathogenesis

Normal circulatory function is maintained by the interplay between the heart and blood flow with the purpose of delivering oxygen and nutrients to the tissues. Cardiac output is calculated by multiplying the stroke volume (volume of blood ejected by the left ventricle in a single beat) by the heart rate (ejection cycles per minute). Stroke volume is dependent on the filling volume of the ventricle (preload), resistance against which the heart is pumping blood (afterload), and myocardial contractility. During childhood, the heart rate is faster, and the stroke volume is smaller than during adulthood. In children, increasing the heart rate is the primary means to increase the cardiac output.

Shock develops as the result of conditions that cause decreased intravascular volume, abnormal distribution of intravascular volume, or impaired cardiovascular function. Children effectively compensate for circulatory insufficiency by increasing their heart rate, systemic vascular resistance (SVR), and venous tone. Children can therefore maintain normal blood pressures despite significantly compromised tissue perfusion. Thus, in pediatric patients, it is especially important to recognize that hypotension is not part of the definition of shock.

The clinical manifestations of shock can be directly related to the abnormalities seen on the tissue, cellular, and biochemical levels. Microcirculatory dysfunction; tissue ischemia; and release of biochemical, vasoactive, and inflammatory mediators are all part of the spectrum of pathophysiologic aberrations seen in shock. Poor perfusion of vital organs results in impaired function. For example, inadequate perfusion of the brain and kidneys results in depressed mental status and decreased urine output, respectively. As poorly perfused cells switch to anaerobic metabolism to generate energy, lactic acid accumulates resulting in a metabolic acidosis that further interferes with cell function. Hypoperfusion also initiates inflammatory events, such as the activation of neutrophils and release of cytokines, that cause cell damage and microischemia.

The prevalence of causes of shock varies by patient age, as well as region of the world. Hypovolemic shock from diarrheal illness is the leading cause of pediatric mortality worldwide, but is very rare in the United States. Congenital lesions (including heart disease) and complications of prematurity are most common in neonates and infants. Malignant neoplasms (for whom infectious complications are prevalent), infectious causes, and unintentional injuries are more common in older children and young adolescents. Injury, homicide, and suicide become more prevalent in older adolescents.

Classification of Shock