Western Journal of Emergency Medicine: Integrating Emergency Care with Population Health

Introduction: The Emergency Severity Index (ESI) is a widely used triage tool in emergency departments (EDs) and is associated with adverse outcomes. Lactate has also been associated with mortality in various ED populations. This study evaluated whether lactate levels measured after triage at the treating physician’s discretion are associated with in-hospital mortality across ESI levels in admitted ED patients.

Methods: This study is a secondary analysis of prospectively collected data from adult patients presenting to the ED of a Swiss tertiary care center in 2013, 2015, 2017, and 2019. The study included admitted patients who underwent post-triage lactate measurement at the treating physician’s discretion. Only the first lactate value measured in the ED was analyzed and categorized as < 2.0, 2.0–3.9, and ≥ 4.0 mmol/L. The primary outcome was in-hospital mortality; secondary outcomes were 30-day mortality and intensive care unit (ICU) admission. Associations were assessed using multivariable logistic regression models adjusted for age and sex. Model discrimination was compared using receiver operating characteristic curve analysis.

Results: Among 3,909 patients admitted from the ED who had a lactate drawn (of 17,327 ED presentations during the study period; 22.6%), the median age was 72 years and 2,062 (52.8%) were male. In-hospital mortality occurred in 168 (4.3%), 30-day mortality in 258 (6.6%), and ICU admission in 698 (17.9%). In ESI levels 2 (n = 1,826) and 3 (n = 1,722), crude in-hospital mortality was similar (59 [3.2%] and 44 [2.6%], respectively), but varied after stratification by lactate level. In ESI level 2 patients, in-hospital mortality occurred in 24 (2.0%) among those with lactate < 2.0 mmol/L (n = 1,210) and in 18 (17.8%) among those with lactate ≥ 4.0 mmol/L (n = 101), corresponding to an age- and sex-adjusted absolute risk difference of 16.0% (95% CI, 8.8–23.3). In ESI level 3, in-hospital mortality occurred in 20 (1.6%) at lactate < 2.0 mmol/L (n = 1,254) and in 8 (15.1%) at lactate ≥ 4.0 mmol/L (n = 53), corresponding to a risk difference of 12.5% (95% CI, 3.7–21.3). Discrimination for in-hospital mortality was higher when lactate was considered alongside ESI (area under the curve [AUC] 0.844 versus 0.799; ΔAUC 0.045, 95% CI, 0.021–0.069), with smaller increases for 30-day mortality and ICU admission.

Conclusion: In admitted ED patients who had lactate measured after triage at physician discretion, higher lactate levels were associated with increased in-hospital mortality across ESI levels, particularly among patients triaged as ESI levels 2 and 3.