Critical Care Medicine

Shock and multiple organ system failure are 2 of the most common and important problems in the intensive care unit (ICU). When tissue oxygen supply decreases in certain forms of shock, increased oxygen extraction occurs to maintain oxygen consumption. If shock continues unabated, oxygen delivery becomes inadequate and anaerobic metabolism ensues, with lactic acidosis. After this critical point, oxygen consumption is said to be delivery-dependent. The blood lactate level correlates well with the degree of perfusion failure and reflects the oxygen debt. In shock due to trauma, hypovolemia, or hemorrhage, it has long been recognized that rapid and aggressive resuscitation results in quicker repayment of this oxygen debt and improved outcome. Some critically ill patients, notably those with trauma or sepsis, are hypermetabolic and may require higher levels of oxygen delivery to maintain oxidative metabolism. Accordingly, it has been hypothesized that increasing oxygen delivery to supranormal levels may be beneficial.