In logistic regression, base sellckchem excess was the sole parameter associated with sodium bicarbonate administration (OR = 0.91, 95% CI = 0.85 to 0.97; P = 0.005). Among the 98 patients who were not treated with sodium bicarbonate within the 24 first hours of their ICU stay, 6 were finally treated after 24 hours and 3 of them died in the ICU.Table 2Admission and outcome characteristics of the 155 patients admitted with severe metabolic or mixed acidosis treated with buffers or not at day 0Bicarbonate administration ranged from 5% of the patients in one ICU to 55% in another one, depending mostly on the center delivering treatment rather than on the acidemia mechanism. When used, the concentration of sodium bicarbonate was 3.5 �� 3.3 mmol/L within the first 24 hours and ranged from 250 ml of 1.

4% solution to 4, 000 ml of 4.2% solution, with no statistical difference observed between survivors and nonsurvivors. The severity of acidemia was not associated with the frequency of sodium bicarbonate prescription, but lower plasma bicarbonate, base excess, PaCO2 and higher corrected anion gap were associated with sodium bicarbonate administration (Table (Table2).2). The different outcome parameters were not different on the basis of early prescription of sodium bicarbonate (Table (Table2).2). Multivariate analysis showed that although plasma pH upon ICU admission was not a predictor of outcome, the persistence of a low plasma pH after 24 hours in the ICU was an independent risk factor for mortality in the ICU (Table (Table3).3). Additional details are provided in the Additional file 1.

Table 3Multivariate logistic regression analysis for mortality analysis: results of stepwise selection proceduresDiscussionThe main results of this study can be summarized as follows. First, severe metabolic or mixed acidemia defined by a plasma pH level lower than 7.20 within the first 24 hours of ICU admission was observed in 6% of critically ill patients. Second, severe metabolic or mixed acidemia was associated with an ICU mortality rate of 57%. Third, as opposed to pH value, the rapidity of acidemia correction was associated with mortality. Fourth, sodium bicarbonate prescription within the first 24 hours of acidemia was heterogeneous, depending on the participating ICU, and was not associated with the patient’s prognosis.Several limitations of this study must be identified.

First, we defined and classified severe acidemia on the basis of a pH value below 7.20, bicarbonate and base excess [3,18,19], and instead used the physiochemical classification developed by Stewart [1,23]. We chose this strategy because of its widespread use and because it was the easiest way to screen patients Anacetrapib [6,24]. Moreover, our study could not demonstrate that acidemia per se rather than the underlying disease was the main independent predictive factor in patient outcome.