Clinical utility of standard base excess in the diagnosis and interpretation of metabolic acidosis in critically ill patients

The aims of this study were to determine whether standard base excess (SBE) is a useful diagnostic tool for metabolic acidosis, whether metabolic acidosis is clinically relevant in daily evaluation of critically ill patients, and to identify the most robust acid-base determinants of SBE. Thirty-one critically ill patients were enrolled. Arterial blood samples were drawn at admission and 24 h later. SBE, as calculated by Van Slyke's (SBEVS) or Wooten's (SBEW) equations, accurately diagnosed metabolic acidosis (AUC = 0.867, 95%CI = 0.690-1.043 and AUC = 0.817, 95%CI = 0.634-0.999, respectively). SBEVS was weakly correlated with total SOFA (r = -0.454, P < 0.001) and was similar to SBEW (r = -0.482, P < 0.001). All acid-base variables were categorized as SBEVS <-2 mEq/L or SBEVS <-5 mEq/L. SBEVS <-2 mEq/L was better able to identify strong ion gap acidosis than SBEVS <-5 mEq/L; there were no significant differences regarding other variables. To demonstrate unmeasured anions, anion gap (AG) corrected for albumin (AGA) was superior to AG corrected for albumin and phosphate (AGA+P) when strong ion gap was used as the standard method. Mathematical modeling showed that albumin level, apparent strong ion difference, AGA, and lactate concentration explained SBEVS variations with an R2 = 0.954. SBEVS with a cut-off value of <-2 mEq/L was the best tool to diagnose clinically relevant metabolic acidosis. To analyze the components of SBEVS shifts at the bedside, AGA, apparent strong ion difference, albumin level, and lactate concentration are easily measurable variables that best represent the partitioning of acid-base derangements.