J-shaped association between 72-hour net fluid balance and 90-day mortality in critically ill patients with cirrhosis: a retrospective cohort study

Abstract Background Critically ill patients with cirrhosis face competing fluid-management demands, with some indications requiring fluid restriction and others requiring aggressive resuscitation. Whether cumulative net fluid balance is related to mortality in a J-shaped fashion, and where any optimal range lies, is unknown. Methods We conducted a retrospective cohort study using the MIMIC-IV database (accessible upon data use agreement). We included adults (≥ 18 years) with cirrhosis admitted to the intensive care unit (ICU). The primary exposure was 72-hour cumulative net fluid balance (NFB72). The primary outcome was 90-day all-cause mortality. We modeled the dose-response relationship with restricted cubic spline (RCS) logistic regression adjusted for twelve prespecified covariates, and tested effect modification by vasopressor use. Results Among 3801 critically ill patients with cirrhosis (median age 60 years; 36.9% female), 781 (20.5%) died within 90 days. NFB72 exhibited a J-shaped association with 90-day mortality (nonlinearity P < 0.0001; ΔAIC − 21.0 versus linear; P for trend = 0.004). Compared with the second quartile (near-neutral balance), the adjusted odds ratio (OR) for 90-day mortality was 2.45 (95% CI 1.78–3.40) in the fourth quartile. The optimal balance point was − 231 mL, corresponding to a minimum predicted risk of 8.2%. The association was modified by vasopressor use (interaction P = 0.007): positive balance was associated with mortality among vasopressor-treated patients (OR 2.89, 95% CI 1.87–4.57) but not among vasopressor-free patients (OR 1.52, 95% CI 0.84–2.71). Conclusions In critically ill patients with cirrhosis, 72-hour net fluid balance showed a J-shaped association with 90-day mortality, with harm more pronounced among vasopressor-treated patients and an optimal balance near zero. These findings support individualized, hemodynamic-status-informed fluid management.