Association between serum direct bilirubin and 90-day mortality in patients with ARDS: A retrospective analysis

The liver plays a key role in the pathogenesis and resolution of acute respiratory distress syndrome (ARDS). Clinically, elevated serum bilirubin - especially direct bilirubin (DBIL) - is frequently observed in ARDS. This study aimed to evaluate the association between DBIL levels and 90-day mortality in ARDS patients. This retrospective cohort study used data from the MIMIC-IV database. ARDS patients were identified based on the Berlin definition. The primary outcome was 90-day all-cause mortality; in-hospital mortality was secondary. Cox proportional hazards models assessed the association between DBIL levels and mortality. Restricted cubic spline regression examined nonlinear relationships. Kaplan-Meier analysis compared survival across DBIL strata. A total of 714 ARDS patients were included. Patients with DBIL > 1.05 mg/dL had worse clinical profiles, including lower arterial pH, higher lactate, elevated ALT, and higher sequential organ failure assessment scores. Kaplan-Meier analysis showed significantly lower survival in the high DBIL group (52.2% vs 73.7%; P < .001). Multivariable Cox analysis showed elevated DBIL was independently associated with 90-day mortality (HR = 1.76; 95% CI = 1.33-2.33; P < .001) and in-hospital mortality (HR =1.99; 95% CI = 1.59-2.50; P < .001). Indirect bilirubin was not significantly associated with 90-day mortality. Restricted cubic spline analysis revealed a nonlinear relationship between DBIL and 90-day mortality (P for nonlinearity = .002). Our study demonstrates that DBIL is independently associated with 90-day mortality in patients with ARDS. Clinicians should consider close monitoring of DBIL levels and adjust management strategies accordingly to improve patient outcomes.