Association between serum direct bilirubin and the 90-days mortality in patients with ARDS

Objective The liver plays a critical role in the pathogenesis and resolution of ARDS. Clinically, ARDS patients often present with elevated bilirubin levels, primarily due to an increase in direct bilirubin (DBIL). This study aimed to investigate the association between serum DBIL levels and 90-day mortality in ARDS patients. Methods We conducted an analysis of patients diagnosed with ARDS according to the Berlin definition using data from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. The primary outcome was 90-day mortality, with in-hospital mortality as the secondary outcome. Multivariable Cox regression assessed the relationship between DBIL and 90-day mortality, while restricted cubic spline regression(RCS) explored potential nonlinear associations. Kaplan-Meier(KM) survival curves compared survival rates between patients with higher and lower DBIL levels. Results A total of 714 ARDS patients enrolled, 266 patients died within 90 days of admission to the ICU. The higher DBIL group exhibited significantly worse clinical outcomes, including lower pH, higher lactate, elevated ALT, and increased SOFA scores. KM survival analysis revealed significantly lower survival rates in the higher DBIL group (52.2% vs. 73.7%, P < 0.001). Multivariable Cox regression analysis showed that higher DBIL levels were independently associated with increased 90-day mortality (HR 1.77, 95% CI: 1.31–2.28, P < 0.001) and in-hospital mortality (HR 1.95, 95% CI: 1.56–2.43, P < 0.001), while indirect bilirubin(IBIL) was not significantly associated with 90-day mortality (HR 0.93, 95% CI: 0.85–1.02, P = 0.127). RCS analysis indicated a nonlinear relationship between DBIL levels and mortality risk. Subgroup analyses showed consistent associations across various patient demographics. Conclusion Our study shows that elevated DBIL is independently associated with 90-day mortality in ARDS patients. Clinicians should closely monitor ARDS management and adjust treatment strategies when DBIL levels are elevated.