Oxygen delivery and consumption in intensive care unit practice : goal-directed therapy

Although the attainment of normal hemodynamic values has always been assumed to be the therapeutic target for critically ill patients, a series of studies reported increased values in oxygen transport variables in survivors of high-risk surgery. It has been supposed that the higher values observed in survivors might indicate a physiological compensation for the increased metabolic requirements due to disease. The logical consequence has been the hypothesis of pushing the hemodynamic values up to a cardiac index (CI) higher than 2.5 l(*)min-1(*)m-2 and oxygen delivery (DO2) higher than 650 ml(*)min-1(*)m-2, which were found to be the threshold values that better discriminate between survivors and non-survivors. To date there are at least nine randomized controlled clinical trials that specifically investigate whether increasing oxygen transport in critically ill patients improves survival. A number of concerns have been raised with each of these studies, and overall the results suggest that outcome is not significantly improved, at least for unselected patients in intensive care units. This conclusion, together with the great concern about the methodology used to study the oxygen supply dependency phenomena, cast serious doubts about the routine use of a strategy to maximize DO2 in unselected critically ill patients.