The intensive care unit is set apart from other hospital patient care areas by (1) physiological instrumentation that permits better assessment and more effective therapy and (2) more intensive nursing. These capabilities allow nurse and physician intensivists to evaluate tissue perfusion and tissue oxygenation by the temporal patterns of oxygen delivery and oxygen consumption, as well as hemodynamics. Such evaluation provides important insight into the functional impairment of hemorrhagic, traumatic, septic, and postoperative shock. Using artificial intelligence-based systems, complex clinical algorithms--tailored to specific patient conditions--have been developed and are described. These algorithms are based on both invasive and noninvasive monitoring systems and on clinical experience with a large series of high-risk surgical patients.