Main comparisons are 28-day and ICU mortality between study groups (chi square test for percentages and log-rank test Kaplan-Meier survival curves. Multiple organ dysfunction score and Sequential Organ Failure Assessment score will be compared at baseline and on days 4, 7, 14 and 28 (Student's t test and/or non-parametric tests). Independent risk factors for mortality will be studied by multivariate analysis (Cox regression) of significant comparisons of the univariate analysis. Analysis sample according to the principle of intention to treat.