The impact of postoperative fluid balance on early hepatic function and renal replacement therapy requirement after liver transplantation: a single-center retrospective cohort study

Liver transplantation (LT) is the definitive treatment for end-stage liver disease, with acute kidney injury (AKI) and renal replacement therapy (RRT) as common severe early complications. Fluid overload (FB) is a key risk factor for renal adverse events, yet the impact of postoperative fluid balance on early liver function recovery and renal outcomes after LT remains to be clarified. A single-center retrospective cohort study was conducted on 511 LT patients (2022–2025), grouped by 5-day postoperative cumulative fluid balance (negative/positive). Propensity score matching (1:1, n = 160) was used to balance baselines. Liver/renal function indices, RRT rate and AKI incidence were compared between groups. Multivariate logistic regression and restricted cubic spline (RCS) analysis were applied to identify RRT risk factors and explore the association between fluid balance and RRT risk. No significant differences in aspartate aminotransferase (AST), alanine aminotransferase (ALT) and total bilirubin (T-Bil) were observed between groups at postoperative days 1, 3 and 5. The negative fluid balance group had lower serum creatinine (Scr) levels, faster Scr decline, and a significantly lower RRT rate (6.3% vs. 18.8%, p = 0.017) than the positive group. Surgical duration (OR = 2.272, p = 0.009), postoperative day 1 ALT (100-unit increase, OR = 1.111, p = 0.006) and fluid balance (1-L increase, OR = 1.125, p = 0.028) were independent RRT risk factors. RCS analysis confirmed increased fluid balance correlated with higher RRT risk. Postoperative fluid balance has no effect on early liver function recovery after LT, while cumulative positive fluid balance is associated with elevated RRT requirement. Surgical duration, postoperative day 1 ALT and fluid balance are independent risk factors for early RRT, highlighting the importance of optimized early fluid management for preventing renal adverse events after LT.