Association between time-weighted average lactate during cardiopulmonary bypass and postoperative infection in patients undergoing cardiac surgery: single-center, prospective cohort study protocol.

INTRODUCTION: During cardiopulmonary bypass (CPB), impaired perfusion, ischemia-reperfusion injury, and systemic inflammation frequently result in lactate accumulation. Lactate is routinely monitored perioperatively and may serve as an early indicator of postoperative infection, yet prospective evidence linking intraoperative lactate to infection risk remains limited. This prospective cohort study aims to evaluate the association between the time-weighted average (TWA) lactate during CPB and the risk of postoperative infection in patients undergoing cardiac surgery. METHODS: This single-center, prospective cohort study will enroll 346 adult patients undergoing elective cardiac surgery with CPB. Arterial blood samples will be obtained at multiple intraoperative time points to calculate TWA lactate. Patients will be classified into exposure and non-exposure groups based on a TWA lactate cutoff of ≥2.0 mmol/L. The primary outcome is the incidence of infection within 30 days of surgery. A predefined directed acyclic graph will guide covariate adjustment. Multivariable logistic regression will estimate the risk association, and restricted cubic spline models will explore potential nonlinear relationships. Sensitivity analyses will use lactate load, defined as the area under the lactate-time curve during CPB, to examine whether cumulative intraoperative lactate exposure yields results consistent with those obtained using TWA. DISCUSSION: This prospective cohort study aims to investigate the association between time-weighted average lactate during cardiopulmonary bypass and postoperative infection risk in cardiac surgery patients. If the hypothesis is confirmed, TWA lactate could serve as a readily available marker for intraoperative risk stratification, facilitating early identification of high-risk patients and guiding individualized interventions. The findings may provide evidence for optimizing perioperative management and improving clinical outcomes. As a single-center study, external validation in multicenter settings will be needed to enhance generalizability. CLINICAL TRIAL REGISTRATION: https://www.chictr.org.cn, identifier ChiCTR2500110269.