The relationship between oxygen delivery and uptake in the critically ill: is there a critical or optimal therapeutic value? A meta-analysis.

In order to identify a critical or an optimal therapeutic value for oxygen delivery and oxygen uptake, we analysed data from 40 publications concerning the relationship between oxygen delivery and consumption in patients with adult respiratory distress syndrome, trauma or during sepsis, and in nonseptic controls. According to the outcome, the patients were allocated to either group 1 (survivors) or group 2 (nonsurvivors). While oxygen delivery and uptake (mean, SEM) were significantly higher in patients with adult respiratory distress syndrome (636, SEM 31 ml.min-1.m-2 and 155, SEM 5 ml.min-1.m-2), trauma (782, SEM 77 ml.min-1.m-2 and 167, SEM 10 ml.min-1.m-2) and sepsis (654, SEM 28 ml.min-1.m-2 and 163, SEM 5 ml.min-1.m-2) than in nonseptic controls (452, SEM 18 ml.min-1.m-2 and 126, SEM 3 ml.min-1.m-2, p < 0.05), there were no significant differences in these parameters between survivors and nonsurvivors. Although therapeutic manoeuvres were effective in increasing both oxygen delivery and consumption, these improvements were not paralleled by an increase in survival rate. The correlation between oxygen delivery and uptake is generally a result of the use of pooled data and therefore prone to mathematical coupling. This is true particularly for patients with adult respiratory distress syndrome and sepsis. Thus, our study failed to identify either an optimal or a critical value of oxygen delivery or oxygen consumption in critically ill patients.