The U-shaped association between serum osmolality and 28-day mortality in patients with acute respiratory failure: a...

Serum osmolality is a potential prognostic biomarker in critical illnesses. However, its predictive value for mortality in patients with acute respiratory failure (ARF) remains unclear. This study aimed to evaluate the association between serum osmolality and 28-day mortality in critically ill patients with ARF.

Patients with ARF were identified from the Medical Information Mart for Intensive Care IV database and grouped into quintiles based on their serum osmolality. Serum osmolality was derived from the first laboratory values obtained during the period from 6 hours before to 24 hours after intensive care unit (ICU) admission. The association between serum osmolality and 28-day mortality was assessed using Cox proportional hazards regression and restricted cubic splines (RCS).

Among the 9,748 patients enrolled, the median age was 68.0 years, 55.0% were male, and the 28-day mortality rate was 25.6%. After multivariable adjustment, patients in the lowest (Q1) and highest (Q5) serum osmolality quintiles had an increased mortality risk compared to Q2: [hazard ratio (HR) =1.17; 95% confidence interval (CI): 1.02-1.35] and (HR =1.30; 95% CI: 1.14-1.49). RCS analysis demonstrated a U-shaped association between serum osmolality and 28-day mortality, and a two-piecewise Cox model identified a threshold at 287.79 mmol/L. Below this threshold, each unit increase in osmolality was associated with lower mortality (HR =0.99; 95% CI: 0.98-0.99), while above it, each unit increase was associated with higher mortality (HR =1.01; 95% CI: 1.01-1.01).

Serum osmolality demonstrated a U-shaped association with 28-day mortality in patients with ARF, suggesting its potential as a biomarker for risk stratification.