The endothelial activation and stress index (EASIX) as a prognostic marker in patients undergoing cardiac surgery

Cardiopulmonary bypass (CPB)-assisted cardiac surgery is associated with endothelial stress, systemic inflammation, and postoperative organ injury. The Endothelial Activation and Stress Index (EASIX), calculated from lactate dehydrogenase, serum creatinine, and platelet count, may provide a simple measure of postoperative physiological stress. This study evaluated the association between early postoperative EASIX and 28-day all-cause mortality in patients undergoing CPB-assisted cardiac surgery. We conducted a retrospective cohort study of 2,233 adult patients undergoing CPB-assisted cardiac surgery in the MIMIC-IV database. Early postoperative EASIX was calculated using the first available lactate dehydrogenase, serum creatinine, and platelet count measured within 24 h after ICU admission; when multiple measurements were available, the earliest valid value for each component was used. The primary analysis evaluated the association between continuous log₂(EASIX) and 28-day all-cause mortality using a fully adjusted Cox proportional hazards model. Tertile-based Cox and Kaplan–Meier analyses, sensitivity analyses, and complete-case analyses incorporating plasma lactate were considered supportive, whereas restricted cubic spline, subgroup, and receiver operating characteristic analyses were considered exploratory. Higher log₂(EASIX) was independently associated with an increased risk of 28-day all-cause mortality after multivariable adjustment (HR 1.12, 95% CI 1.03–1.21; P = 0.01). Tertile-based and Kaplan–Meier analyses showed poorer survival among patients with higher EASIX, while restricted cubic spline analysis suggested a nonlinear increase in mortality risk at higher EASIX levels. The association was consistent across sensitivity analyses, including after re-inclusion of patients with ICU stays shorter than 24 h. Among patients with available plasma lactate measurements, EASIX remained independently associated with mortality after adjustment for lactate. Higher early postoperative EASIX was independently associated with 28-day all-cause mortality after CPB-assisted cardiac surgery. EASIX may serve as a simple adjunct to established postoperative risk assessment.