Severe sepsis is characterized by increased oxygen demand, alteration of oxygen extraction, and a diminution of myocardial contractility. The importance of each of these three factors is directly related to the severity of the sepsis. The combination of these factors may lead to tissue hypoxia, which is the shortest route to development of multiple organ failure (MOF). The presence of tissue hypoxia should be suspected in the presence of lactic acidosis. The phenomenon of dependence on oxygen consumption (VO2) in relation to oxygen transport (DO2) is detectable where there is a rise in DO2 induced by perfusion of liquids or administration of vasoactive agents. Study of the relationship between cardiac flow and oxygen extraction is a simple means of studying the relations between VO2 and DO2 at the patient's bedside.