Trajectory of serum osmolality changes and 28-day mortality risk in patients with sepsis-associated delirium based on the MIMIC-IV database.

Serum osmolality (SOSM) levels have been reported to be associated with the prognosis of critically ill patients. The purpose of this study was to analyze the impact of the trajectory of changes in SOSM on the 28-day mortality risk in patients with sepsis-associated delirium (SAD). Latent class trajectory modeling (LCTM) was employed in this retrospective cohort study of patients with SAD from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. SOSM trajectories were derived using LCTM based on three measurements obtained at two-day intervals during the first six days following ICU admission. The relationship between the SOSM and 28-day mortality risk was explored using restricted cubic spline (RCS), Cox regression models, and Kaplan-Meier curves. Subgroup analyses were conducted to examine the association and stability of SOSM trajectories with SAD patients' outcome. Among the 3100 SAD patients included in the analysis, 488 (15.7%) died within 28 days. The median SOSM level was 294.8 (IQR 288.1-302.0) mmol/L. LCTM identified four distinct SOSM trajectories: normal-level-steady trend trajectory (Class 1), normal-level-increasing trend trajectory (Class 2), normal-level-decreasing and then increasing trend trajectory (Class 3), and normal-level-increasing and then decreasing trend trajectory (Class 4). Elevated baseline SOSM levels were independently associated with higher 28-day mortality (HR 1.02, 95% CI 1.01-1.03). RCS revealed a positive linear association between baseline SOSM levels and 28-day mortality risk (P overall < 0.001; P non-linearity = 0.87). Compared with Class 1, patients in Class 2 (HR 1.62, 95% CI 1.31-2.01), Class 3 (HR 1.71, 95% CI 1.19-2.47), and Class 4 (HR 1.99, 95% CI 1.39-2.84) exhibited significantly increased 28-day mortality risk. Subgroup analyses further demonstrated that the trajectory 2 was consistently associated with 28-day mortality in SAD patients aged over 60 years. SOSM was an independent risk factor for 28-day mortality in patients with SAD. Persistent elevation and fluctuation of SOSM trajectories after ICU admission were associated with increased 28-day mortality in patients with SAD.