PROGNOSTIC SIGNIFICANCE OF STANDARD BASE AND SERUM LACTATE EXCESS IN CRITICALLY ILL PATIENTS

Abstract

Background: Elevated serum lactate and deranged base excess are common in critically ill patients and associated with adverse outcomes. While both reflect metabolic disturbance and tissue hypoperfusion, their relative prognostic value remains unclear, particularly in resource-limited settings where arterial blood gas analysis is readily available but serial lactate measurement may be constrained. This study aimed to evaluate the prognostic significance of admission standard base excess (SBE) and serum lactate for predicting ICU mortality in a mixed medical-surgical critically ill population.

Methods: This prospective observational study was conducted in a 12-bed multidisciplinary ICU over 12 months. Adult patients (n=150) admitted with expected ICU stay ≥24 hours underwent arterial blood gas analysis including SBE and simultaneous serum lactate measurement at admission. Primary outcome was ICU mortality. Discriminative performance was assessed using receiver operating characteristic curve analysis, and multivariable logistic regression evaluated independent associations with mortality, adjusting for age and APACHE II score.

Results: Overall ICU mortality was 30% (45/150). Non-survivors had significantly higher admission lactate [4.1 (IQR 2.9–5.3) vs 2.1 (IQR 1.3–3.2) mmol/L, p<0.001] and more negative SBE (−6.8±4.2 vs −2.9±3.6 mmol/L, p<0.001) compared with survivors. Admission lactate demonstrated superior discriminative ability (AUC 0.78, 95% CI 0.70–0.86) compared with SBE (AUC 0.69, 95% CI 0.60–0.78). In multivariable analysis, admission lactate (adjusted OR 1.28 per mmol/L, p=0.003) and APACHE II score (adjusted OR 1.12 per point, p<0.001) remained independent predictors of mortality, whereas SBE was not independently associated (adjusted OR 1.06, p=0.19). Combining SBE with lactate yielded modest, non-significant improvement in AUC (0.81 vs 0.78, p=0.09). Lactate ≥4 mmol/L was present in 51.1% of non-survivors versus 14.3% of survivors and associated with longer ICU stay (median 7 vs 4 days) and greater need for organ support.

Conclusion: Admission serum lactate is a stronger independent predictor of ICU mortality than standard base excess in critically ill adults and should be prioritized for early risk stratification. While SBE correlates with illness severity and outcomes, it does not provide substantial additional prognostic value beyond lactate and APACHE II score in multivariable models. Standard base excess remains clinically useful for characterizing metabolic acid-base disturbances and may serve as a surrogate when lactate measurement is delayed or unavailable.