Background
Open cardiac surgery involving cardiopulmonary bypass (CPB) triggers a systemic inflammatory response that significantly affects clinical outcomes. However, the dynamics and specific roles of cytokine release after CPB in the pediatric population remain unclear.

Purpose
To evaluate the dynamics of cytokine levels and their association with low cardiac output syndrome (LCOS)-related outcomes.

Methods
A prospective observational cohort study was conducted of 32 children who underwent elective open cardiac surgery with CPB at Songklanagarind Hospital, Thailand. Levels of interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor (TNF)-α were analyzed preoperatively and immediately (T0), 6, 12, and 24 hours after intensive care unit admission. LCOS-related outcomes were defined with at least two of the following criteria being met within 24 hours postoperative: clinical and laboratory parameters, vasopressor-inotropic score ≥20, ejection fraction <50% on echocardiography; and requirement for a serious postoperative intervention. Statistical analyses utilized linear mixed models and multivariate logistic regression to identify the independent predictors of LCOS.

Results
The mean patient age was 34.8±34.4 months; 56.2 % were male. Roughly one-third (37.5%) had a history of previous cardiac surgery, while one-quarter (28.3%) had a Risk Adjustment for Congenital Heart Surgery score ≥3. LCOS-related outcomes occurred in 37.5% of patients. IL- 6, IL-8, and TNF-α levels differed significantly between patients with and without LCOS outcomes. An increase in IL-8 of >56 pg/mL from baseline to T0 showed the strongest association with LCOS (odds ratio, 37.34; 95% confidence interval, 4.53–836.53).

Conclusion
An elevated postoperative IL-8 level is a robust predictor of LCOS-related outcomes in pediatric patients undergoing cardiac surgery. These findings emphasize the importance of monitoring cytokine dynamics to guide interventions and improve patient outcomes.