Admission lactate and in-hospital mortality in elderly patients with sepsis receiving invasive mechanical ventilation: a multicenter retrospective cohort study

Elderly patients with sepsis requiring invasive mechanical ventilation are at high risk of death. However, the prognostic value of admission lactate in this specific population remains incompletely characterized. This multicenter retrospective cohort study used the eICU Collaborative Research Database, a de-identified United States intensive care unit database, and included 2,981 patients aged ≥ 65 years with sepsis who received invasive mechanical ventilation. The exposure was the first lactate measured within 24 h after intensive care unit admission, and the primary outcome was in-hospital mortality during the index hospitalization. Multivariable logistic regression was performed after adjustment for 12 predefined covariates: age, sex, body mass index, APACHE IV score, Glasgow Coma Scale, creatinine, albumin, hemoglobin, diabetes, chronic obstructive pulmonary disease, congestive heart failure, and hypertension. Generalized additive modeling assessed non-linearity, exploratory two-piecewise logistic regression evaluated a possible threshold effect, and receiver operating characteristic analysis assessed discrimination. Overall in-hospital mortality was 38.0%. Mortality increased across lactate tertiles, from 27.8% in the low-lactate group (0.2–1.7 mmol/L) to 35.5% in the medium-lactate group (> 1.7–3.4 mmol/L) and 50.8% in the high-lactate group (> 3.4–27.1 mmol/L) (p < 0.001). Each 1 mmol/L increase in lactate was associated with higher mortality in univariable analysis (OR 1.183, 95% CI 1.151–1.215; p < 0.001) and remained independently associated after full adjustment (adjusted OR 1.138, 95% CI 1.105–1.172; p < 0.001). Non-linearity was observed. In exploratory threshold analysis, the best-fitting cutoff was 3.2 mmol/L; however, model improvement was modest. Lactate alone showed modest discrimination (AUC 0.630, 95% CI 0.609–0.650). Higher admission lactate was independently associated with greater in-hospital mortality in elderly septic patients receiving invasive mechanical ventilation. The association appeared non-linear, but the identified threshold was exploratory and requires external prospective validation.