Arterial base deficit/excess (BD/E) is commonly used marker of metabolic acidosis in critically ill patients, but requires an arterial puncture and blood gas analysis. We hypothesized that serum bicarbonate (HCO3), which can be routinely obtained, strongly correlates with arterial BD/E and provides equivalent predictive information. In addition, we evaluated predictive value of simplified acute physiology score III (SAPS III). Total of 152 critically ill surgical patients were included in retrospective analysis. On admission to intensive care unit sets of simultaneously obtained paired laboratory data, including an arterial blood gas and serum chemistry panel with serum HCO3 were obtained. Very strong correlation between BD/E and simultaneously measured serum HCO3 levels was found (r = 0.857, R(2) = 0.732, p < 0.01). The serum HCO3 level reliably identified a significant metabolic acidosis (AUC = 0.761, p < 0.05). BD and SAPS III were good predictors of mortality (AUCs 0.70 and 0.74, respectively). Serum HCO3 may be used as substitute to detect severe metabolic acidosis. BD and SAPS III score were good predictors of mortality.