Calculated serum osmolarity distribution in critically ill patients with acute pancreatitis: a retrospective cohort study

This study aims to investigate the relationship between calculated serum osmolarity levels and 90-day mortality in patients with acute pancreatitis (AP), an association that remains understudied in the intensive care unit (ICU). This study utilized clinical data from patients diagnosed with AP in the Medical Information Mart for Intensive Care database. Localized Weighted Scatterplot Smoothing (LOWESS) regression, Restricted Cubic Spline (RCS) analysis, and the U test were employed to examine the nonlinear relationship between calculated serum osmolarity and patient outcomes. Additionally, multivariate logistic regression analysis was applied to assess the impact of calculated serum osmolarity on prognosis after adjusting for potential confounding factors such as Demographic data, disease severity scores, and comorbidities. The study included 2046 patients with AP. Calculated serum osmolarity levels differed significantly between survivors and non-survivors (302.4 ± 14.9 vs. 308.9 ± 19.6 mOsm/L, P < 0.001). Both univariate and multivariate logistic regression analyses demonstrated that calculated serum osmolarity was an independent prognostic factor for 90-day mortality (P < 0.05 in both analyses). LOWESS regression, RCS analysis, and U-test results revealed a U-shaped relationship between calculated serum osmolarity and 90-day mortality, with an inflection point (lowest mortality risk) at 293.3 mOsm/L. The excessively high calculated serum osmolarity levels were associated with increased mortality risk (P < 0.05). Subgroup analysis revealed that high calculated serum osmolarity was significantly associated with higher 90-day mortality (P < 0.05). Survival analysis revealed a significant increase in mortality risk when calculated serum osmolarity reached the fourth quartile or higher (all P < 0.05), whereas no significant differences were observed among lower quartile groups. The results of this study indicate that calculated serum osmolarity levels exhibit a U-shaped correlation with 90-day all-cause mortality among patients with AP admitted to the ICU, with high calculated serum osmolarity serving as an independent risk factor for 90-day mortality.