Circulatory Shock: A Microcirculatory Defect

Abstract

The pathophysiological defect which characterizes shock is that of perfusion failure in which blood flow to maintain the function of vital organ systems is critically reduced. As a clinical syndrome, it is characterized by protracted prostration, pallor, coldness and moistness of the skin, collapse of the superficial veins, alterations in pressure is typically less than 90 mmHg or has declined more than 50 mm from the basal level, and the urine flow is less than 20 ml/h. Because of the decrease in renal perfusion, the concentrating capability of renal tubules is impaired, and the urine is typically iso-osmolal. Accordingly, the ratio between urine osmolality and plasma osmolality, which reflects tubular concentrating function of the nephron, is characteristically less than 1.5. A reduction in peripheral blood flow accounts for cold, cyanotic extremities.