Association of preoperative lactate concentration with in-hospital mortality after emergency surgery

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INTRODUCTION Lactate is widely used as a marker of metabolic and circulatory stress, but its prognostic value in emergency surgical populations remains incompletely defined. METHODS We performed a retrospective cohort study using the INSPIRE dataset, including emergency surgical procedures with a preoperative lactate measurement obtained within 6 hours of incision. The primary outcome was in-hospital mortality. Multivariable logistic regression adjusted for age, sex, ASA physical status, surgical department, anaesthesia type, preoperative haemoglobin and creatinine. Lactate was analysed using restricted cubic splines and in prespecified categories (<2, 2-<4 and ≥4 mmol l-¹). Incremental prognostic value was assessed by comparing a baseline clinical model with and without lactate. RESULTS The analytic cohort included 3729 emergency surgical procedures, of which 360 resulted in in-hospital death (9.7%). Mortality increased across lactate categories: 6.9% for lactate <2 mmol l-¹, 13.9% for lactate 2-<4 mmol l-¹ and 42.2% for lactate ≥4 mmol l-¹. After adjustment, lactate was still associated with mortality (odds ratio 1.79 [95% CI 1.23-2.59] for 2-<4 mmol l-¹ and 7.34 [4.65-11.57] for ≥4 mmol l-¹ vs <2 mmol l-¹). Adding lactate to the standard clinical model improved discrimination (AUC 0.755 vs 0.801) and reduced the Brier score (0.094 vs 0.088). Results were consistent across alternative measurement windows and after multiple imputation. CONCLUSION Preoperative lactate concentration was strongly associated with in-hospital mortality and provided incremental prognostic information beyond routinely available variables. In emergency surgical pathways, lactate may support early risk stratification.