Serum lactate is an independent predictor of hospital mortality in critically ill patients in the emergency department: a retrospective study

Background: Elevated lactate has been found to be associated with a higher mortality in a diverse patient population. The aim of the study is to investigate if initial serum lactate level is independently associated with hospital mortality for critically ill patients presenting to the Emergency Department.

Methods: Single-center, retrospective study at a tertiary care hospital looking at patients who presented to the Emergency Department (ED) between 2014 and 2016. A total of 450 patients were included in the study. Patients were stratified to lactate levels: <2 mmol/L, 2-4 mmol/L and >4 mmol/L. The primary outcome was in-hospital mortality. Secondary outcomes included 72-h hospital mortality, ED and hospital lengths of stay.

Results: The mean age was 64.87 ± 18.08 years in the <2 mmol/L group, 68.51 ± 18.01 years in the 2-4 mmol/L group, and 67.46 ± 17.67 years in the >4 mmol/L group. All 3 groups were comparable in terms of age, gender and comorbidities except for diabetes, with the 2-4 mmol/L and >4 mmol/L groups having a higher proportion of diabetic patients. The mean lactate level was 1.42 ± 0.38 (<2 mmol/L), 2.72 ± 0.55 (2-4 mmol/L) and 7.18 ± 3.42 (>4 mmol/L). In-hospital mortality was found to be 4 (2.7%), 18(12%) and 61(40.7%) patients in the low, intermediate and high lactate groups respectively. ED and hospital length of stay were longer for the >4 mmol/L group as compared to the other groups. While adjusting for all variables, patients with intermediate and high lactate had 7.13 (CI 95% 2.22-22.87 p = 0.001) and 29.48 (CI 95% 9.75-89.07 p = <0.001) greater odds of in-hospital mortality respectively.

Discussion: Our results showed that for all patients presenting to the ED, a rising lactate value is associated with a higher mortality. This pattern was similar regardless of patients' age, presence of infection or blood pressure at presentation.

Conclusion: Higher lactate values are associated with higher hospital mortalities and longer ED and hospital lengths of stays. Initial ED lactate is a useful test to risk-stratify critically ill patients presenting to the ED.