Evaluation of the Prognostic Value of Lactate and Acid-Base Status in Patients Presenting to the Emergency Department

Background Lactate levels predict mortality in a wide range of patients presenting to the Emergency Department (ED); however, the effect of co-existing acidosis is unknown. Here, we investigated the effect of acidosis on in-hospital mortality for patients with hyperlactataemia. Methodology This is a retrospective cohort study of adults cared for in the resuscitation area of one ED who received a metabolic panel on arrival. The primary outcome was in-hospital mortality for patients with normal lactate (0.0-2.0 mmol/L), intermediate lactate (2.1-4.0 mmol/L), or high lactate (>4.0 mmol/L), with and without acidosis. Odds ratios (ORs) were calculated to assess the differences in mortality rates between groups stratified by lactate and acid-base status. Results A total of 4,107 metabolic panels were collected and 3,238 were assessed. In total, 510 (15.8%) and 784 (24.2%) patients had a normal lactate and acidosis/no acidosis; 587 (18.1%) and 842 (26.0%) had intermediate lactate and acidosis/no acidosis; and 388 (12.0%) and 127 (3.9%) had high lactate and acidosis/no acidosis, respectively. The overall mortality was 5%. Mortality was 4.3%/0.6% in the normal lactate, 5.6%/2.6% in the intermediate lactate, and 19.3%/3.9% in the high lactate groups, with and without acidosis, respectively. Combining base excess <-6 and lactate >4 mmol/L had a sensitivity of 39%, specificity of 96%, positive predictive value of 32%, and negative predictive value of 98% for in-hospital mortality (OR: 14.0; 95% confidence interval: 9.77-20.11). Conclusions In an undifferentiated cohort of ED patients presenting to the resuscitation area lactaemia associated with acidosis is a more accurate predictor of in-hospital mortality than hyperlactataemia.