Intraoperative peak lactate as a predictor of in-hospital mortality following non-cardiac emergency surgery: a retrospective cohort study

Background The association between intraoperative lactate levels and postoperative prognosis following emergency surgery remains inconclusive. We aimed to investigate the prognostic significance of intraoperative lactate levels in predicting in-hospital mortality. Methods This single-center, retrospective, observational study was conducted at Peking Union Medical College Hospital from 2017 to 2023. Intraoperative peak lactate levels were analyzed using a restricted cubic spline (RCS) model, with in-hospital mortality designated as the primary outcome. Secondary outcomes were length of stay, ICU stay, and ventilation duration. Prespecified subgroup analyses (by ASA grade and surgery type) and a sensitivity analysis excluding in-hospital deaths for secondary endpoints were performed. Results Among the 2,452 patients included in the study, 161 died postoperatively. Both univariate and multivariate regression analyses demonstrated that the intraoperative peak lactate level was associated with perioperative mortality (odds ratio OR 1.306, 95% CI 1.262–1.352, P < 0.001; OR 1.249, 95% CI 1.185–1.318, P < 0.001). The association was consistent across surgery types and appeared stronger in patients with higher ASA grade. The restricted cubic spline model indicated higher intraoperative peak lactate levels were nonlinearly associated with increased in-hospital mortality. Length of hospital stay (LOS), LOS in the intensive care unit (ICU), and duration of mechanical ventilation exhibited a nonlinear (inverted U-shaped) pattern relationship with intraoperative peak lactate levels, with an initial increasing trend followed by a subsequent decline as peak lactate concentrations rose. Conclusions Intraoperative peak lactate levels showed a dose-dependent nonlinear association with increased in-hospital mortality following emergency surgery and play a significant role in predicting postoperative mortality in noncardiac emergency surgery patients. Trial registration Not applicable.