Pathophysiology of critical ill patients: focus on critical oxygen delivery.

Critical ill patients experience acute physiological changes because the body cannot fulfill the oxygen demand to perform normal aerobic metabolism. Factors determining oxygen delivery include cardiac output, hemoglobin, and oxygen saturation. Incapability to fulfill adequate oxygen of the body to produce adenosine triphosphate (ATP) may occur due to decreased oxygen delivery and/or increased oxygen consumption. A condition in which oxygen consumption becomes very dependent on oxygen delivery is called critical oxygen delivery. Parameters to evaluate the adequate oxygen delivery to meet the oxygen consumption are central vein oxygen saturation (SvO2), serum lactate, oxygen extraction ratio (O2ER). A comprehension about oxygen delivery and consumption is very important to overcome tissue hypoxia and various factors in critical ill patients.