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BackgroundThis study aimed to investigate the association between serum magnesium trajectory and risk of in-hospital mortality in intensive care unit (ICU) patients with sepsis.MethodsAdult sepsis patients who had complete data on serum magnesium at ICU admission (at 0, 12, 24, 36 and 48 hours after ICU admission) based the 2012-2019 Medical Information Mart for Intensive Care IV (MIMIC-IV) database were included in this retrospective cohort study. Serum magnesium trajectories were identified using K-means cluster analysis. The multivariable Cox proportional-hazards model was used to evaluate the association between magnesium level at different time points or magnesium trajectory and in-hospital mortality.ResultsA total of 2,270 patients with sepsis were enrolled, and in-hospital mortality occurred in 716 (31.54%). Three trajectories were identified: a high-level declining trajectory, normal-level stable trajectory, and low-level rising trajectory. Among the magnesium levels at different time points, a higher serum magnesium level only at ICU admission (0h) (hazard ratio [HR] = 1.13, 95% confidence interval [CI]: 1.03-1.23) was associated with an increased risk of in-hospital mortality. Compared with the normal-level stable trajectory group, patients in the low-level rising trajectory group (HR = 0.82, 95%CI: 0.70-0.97) had a reduced risk of in-hospital mortality, but no association with in-hospital mortality was found in patients in the high-level declining trajectory group (p=0.812). Conclusion: Sepsis patients with a low-level, rising magnesium trajectory may have a reduced risk of in-hospital mortality.