Association between lactate and 28-day mortality in elderly patients with sepsis among different BMI groups:a cohort study

Introduction:The purpose of this study is to explore the association of baseline lactate level with 28-day mortality in elderly sepsis patients among different Body Mass Index (BMI) groups after ICU admission. Methods:In this retrospective cohort study,a total of 5699 patients with sepsis and age > 65 years were include from the Electronic Intensive Care Unit (eICU) Collaborative Research Database (eICU-CRD) from 208 distinct ICUs across the United States in 2014–2015.Lactate level and BMI at admission were obtained,and the outcome indicator was all-cause mortality within 28 days after ICU admission. A two-segment linear regression model was performed to verify the threshold effects of lactate on outcome and its differences among different BMI.Smooth curve fitting were also performed. Results:The ICU 28-day mortality of elderly sepsis patients in this study was 12.56%(n = 716). After adjustment for potential cofounders,for per 1mmol/L increase in lactate,the odds ratio(OR) of ICU 28-day mortality was 1.195(95%CI 1.136–1.257,P < 0.00001).Smooth fitting curves indicated a non-linear positive relationship between lactate and ICU 28-day mortality,with the turning point of lactate level was 5.5mmol/L.Below this threshold, each 1mmol/L increase in lactate increased the mortality risk by 37.5% (effect size 1.375, 95% CI 1.230–1.536, P < 0.0001).Results showed that the relationship between lactate and 28-day mortality exhibited different nonlinear patterns across BMI groups. Notably, in the group with BMI < 25, a significant increase in mortality risk was observed when lactate concentration was below 3.2mmol/L (1.630, 95% CI: 1.161, 2.287, P = 0.0047), while above this breakpoint, the increase in mortality risk was smaller (1.186, 95% CI: 1.024, 1.373, P = 0.0228). This pattern was also observed in the group with BMI ≥ 30, but the breakpoint effect was not significant in the group with BMI between 25 and 30. Conclusion: In critically ill patients with sepsis(age > 65 years) in ICU,a non linear positive relationship was discovered between lactate and ICU 28-day mortality.And the impact of lactate concentration on ICU 28-day mortality is not only related to lactate levels themselves but is also significantly influenced by BMI.This insight is crucial for clinicians in assessing patient mortality risk.