The main causes of death were refractory hypoxemia (64%); followed by multiorgan dysfunction syndrome (15%) and shock (10%). Prolonged mechanical ventilation and long ICU and hospital stays were frequent (Table 1) . Tracheostomy was performed in 29 patients (16%) at Day 14 [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] . Acid-base variables and fluid balance (Table 3) Arterial pH increased over time in the whole cohort and in both subgroups, perhaps secondary to general resuscitation measures. Despite this, non-survivors displayed significantly lower pH at all time points, owing to changes in base excess on Days 0 and 3, and to pCO 2 elevations thereafter. Respiratory rates remained unchanged, only increasing at Day 10 in non-survivors; nevertheless, this corresponded to the highest pCO 2 values, indicating the more severe respiratory compromise. Bicarbonate paralleled pH behavior. Changes in fluid balance did not show clear trends: only at Day 10 they decreased significantly, expressing survivors' behavior.