Postoperative Infection Mediates and Modifies the Effect of Risk Adjustment for Congenital Heart Surgery-1 Category on Hospital Stay in Pediatric Cardiac Surgery: A Retrospective Cohort Study

OBJECTIVES: To investigate whether postoperative infection mediates and/or modifies the effect of surgical complexity, as defined by the Risk Adjustment for Congenital Heart Surgery (RACHS-1) category, on hospital length of stay (LOS) in pediatric cardiac surgery patients. DESIGN: Retrospective cohort study. SETTING: Tertiary pediatric cardiac center at Xinhua Hospital, Shanghai Jiao Tong University. PATIENTS: A total of 1244 children who underwent congenital heart surgery between October 2020 and July 2024. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Multivariable regression and causal-mediation analyses were performed to estimate the direct and infection-mediated effects of surgical complexity on LOS. Higher-RACHS-1 categories and postoperative infection were independently associated with prolonged LOS (all p < 0.001). In negative binomial mediation analysis, infection mediated 17.4% of the total RACHS-LOS association for RACHS-1 category greater than or equal to 5 vs. 1, corresponding to an infection-mediated increase of 3.87 expected LOS days (95% CI, 1.70-6.42). Infection also modified the association between surgical complexity and LOS, with infection-associated excess LOS increasing to +16.73 days in RACHS-1 category greater than or equal to 5 vs. 1. Mediation was strongest among infants less than or equal to 1 year (28% for RACHS-1 category 3 vs. 1). CONCLUSIONS: Postoperative infection both mediates and amplifies the impact of surgical complexity on hospital LOS, particularly in high-risk infants. Targeted infection-prevention strategies are essential to reduce postoperative morbidity in this population.