The study investigated the prognostic value of lactic base excess (ABE) measurements in 521 adult patients with sepsis, with measurements taken at intervals of up to 48 hours from admission. The overall 28-day mortality was 35.9%, with non-survivors having a more severe metabolic disorder on admission with higher lactate levels and lower ABE values. Patients with a persistently low ABE trajectory (values below 0 during all measurements) had the highest mortality of 52.9% compared to 19.8% in those whose ABE normalized. Each 1 mmol/L increase in ABE over 48 hours was associated with a 25% relative reduction in the risk of death. Failure to normalize ABE within the first 48 hours identifies a high-risk phenotype of patients with sepsis. Serial measurements of ABE provide independent prognostic information and may help identify patients at higher risk of death from sepsis.