Preoperative serum albumin levels as predictors of postoperative morbidity in pediatric congenital heart surgery: a retrospective cohort study

Background: Severe congenital heart disease often requires cardiopulmonary bypass (CPB) surgery. Preoperative hypoalbuminemia may adversely affect postoperative recovery; however, the dose–response relationship between preoperative serum albumin levels and early postoperative adverse events remains unclear. Methods: This retrospective cohort study included 1033 pediatric patients with congenital heart disease who underwent CPB surgery between 2018 and 2024. The primary exposure was the preoperative serum albumin level. The primary outcome was early postoperative adverse events, defined as a composite endpoint including mortality, reintubation, prolonged mechanical ventilation, and extended hospitalization. Patients without these events were classified as the non-adverse outcome group. Multivariable logistic regression models were used to evaluate the association between preoperative albumin levels and postoperative outcomes. Restricted cubic spline (RCS) analysis was performed to assess potential nonlinear relationships. Subgroup analyses based on relevant baseline characteristics were considered exploratory and hypothesis-generating. Results: In the fully adjusted model, compared with the lowest quartile, the second and fourth quartiles of preoperative albumin were associated with significantly lower risks of adverse postoperative outcomes, with odds ratios (ORs) of 0.542 (95% CI: 0.328–0.889) and 0.466 (95% CI: 0.268–0.795), respectively. RCS analysis demonstrated a gradual reduction in adverse outcome risk with increasing albumin levels, with the protective effect plateauing at approximately 40.65 g/L. When albumin levels were ≤40.65 g/L, each incremental increase was associated with a significantly reduced risk of adverse outcomes (OR = 0.864; 95% CI: 0.755–0.983; P = 0.030). Above this threshold, the association was no longer statistically significant (OR = 0.997; 95% CI: 0.885–1.120; P = 0.965). Conclusions: Preoperative serum albumin levels were nonlinearly associated with early postoperative adverse outcomes in pediatric patients undergoing congenital heart surgery. Higher albumin levels within the lower-to-mid physiological range were associated with improved postoperative outcomes, whereas further increases provided no additional apparent benefit. These findings are exploratory and require confirmation in prospective multicenter studies.