Course of Lactate, pH and Base Excess for Prediction of Mortality in Medical Intensive Care Patients - A Retrospective Cohort Analysis

Background: We aimed to evaluate the value of lactate, base excess and pH for prediction of mortality in the course of the disease of medical intensive care patients. Methods: For lactate, pH and base excess, values at the admission to intensive care unit (ICU), at 24 ± 4 hours, maximum / minimum in the first 24 hours and in 24 – 48 hours after admission were collected from all patients admitted to the Medical ICU of the University Hospital Tübingen between January 2016 until December 2018 and investigated for prediction of in-hospital-mortality.Results: Mortality in the cohort of 4067 patients was 22 % and significantly correlated with all evaluated parameters. Strongest predictors of mortality determined by ROC were maximum lactate in 24 h (AUROC 0.74, cut off 2.7 mmol/L, hazard ratio of risk group with value > cut off 2.27) and minimum pH in 24 h (AUROC 0.71, cut off 7.43, hazard ratio for risk group 2.94). Kaplan Meier Curves stratified across these cut offs showed early and clear separation. Hazard ratios per standard deviation were highest for maximum lactate in 24 h (HR 1.65), minimum base excess in 24 h (HR 1.56) and minimum pH in 24 h (HR 0.75). In multiple logistic regression analysis, age, minimum pH in 24 h, pH at 24 h after admission, maximum lactate in 24 h, maximum lactate in 24 – 48 h, minimum base excess in 24 h and minimum base excess in 24 – 48 h were independent predictors of mortality. Conclusions: Lactate, pH and base excess were all suitable predictors of mortality in internal ICU patients, with maximum / minimum values in 24 and 24-48 h after admission altogether stronger predictors than values at admission. Base excess and pH were not superior to lactate for prediction of mortality.