Lactic acidosis not hyperlactatemia as a predictor of in hospital mortality in septic emergency patients.

OBJECTIVE: To compare the prognostic abilities of lactic acidosis and hyperlactatemia and determine the influence of metabolic acidosis when attempting to predict the outcome of septic patients using serum lactate levels.

METHOD: 126 patients with severe sepsis or septic shock were prospectively included in this study at an emergency department. Haemodynamic variables, simplified acute physiology score (SAPS) II, arterial blood gas studies and serum lactate levels were obtained at the time of presentation (0 h) and 4 h after presentation. The probability of mortality was calculated using SAPS II scores and compared with actual inhospital mortality at different serum lactate levels and arterial pH. Survival curves for lactic acidosis and severe hyperlactatemia were analysed using the Kaplan-Meier method.

RESULTS: The calculated probability of mortality decreased from 35.7% (95% CI 30.2 to 41.2) at presentation to 29.3% (95% CI 24.2 to 34.4) at 4 h post-presentation. 27.0% of patients (34) died in hospital. Arterial pH and SAPS II scores were independent factors for predicting mortality of septic patients, at 0 h and 4 h. Serum lactate levels were closely related to severity of illness and metabolic acidosis in septic patients. Patients with lactic acidosis had significantly higher inhospital mortality than patients with normal pH and normal lactate levels by Kaplan-Meier survival analysis as determined based on measurements made at 0 h and 4 h (p<0.001, p<0.001 by the log-rank test, respectively). No significant difference in survival was found between patients with hyperlactatemia and those with normal pH and serum lactate levels.

CONCLUSION: Lactic acidosis not hyperlactatemia was found to predict inhospital mortality more exactly in severe sepsis and septic shock patients. The acid-base state should be considered when attempting to predict the outcome of septic patients using serum lactate levels.