Circulatory shock can be defined today as an imbalance between oxygen demand and oxygen supply, resulting in the development of lactic acidosis. The correction of the tissue hypoxia is usually achieved by an increase in oxygen transport following the administration of oxygen, blood, and other fluids and sometimes vasoactive agents. A reduction in the metabolic needs sometimes can contribute to correcting the oxygen deficit. The adequacy of oxygen supply can be assessed by monitoring either blood lactate levels or oxygen consumption immediately before and after an abrupt increase in oxygen transport.