Prognostic Utility of Initial Lactate in Patients With Acute Drug Overdose: A Validation Cohort

Abstract

Study objective: Previous studies have suggested that the initial emergency department (ED) lactate concentration may be an important prognostic indicator for inhospital mortality from acute drug poisoning. We conduct this cohort study to formally validate the prognostic utility of the initial lactate concentration in a larger, distinct patient population with acute drug overdose.

Methods: This observational, prospective, cohort study was conducted during 5 years at 2 urban teaching hospitals. Consecutive adult ED patients with acute drug overdose had serum lactate levels tested as part of clinical care. The primary outcome was inpatient fatality. Receiver operating characteristics were plotted to determine optimal cut points, test characteristics, area under the curve, odds ratios, and 95% confidence intervals (CIs).

Results: Of 3,739 patients screened, 1,406 were analyzed (56% women; mean age 43.1 years) and 24 died (1.7%). The difference in mean initial lactate concentration was 5.9 mmol/L (95% CI 3.4 to 8.1 mmol/L) higher in patients who died compared with survivors. The area under the curve for prediction of fatality was 0.85 (95% CI 0.73 to 0.95). The optimal lactate cut point for fatality was greater than or equal to 5.0 (odds ratio 34.2; 95% CI 13.7 to 84.2; 94.7% specificity). Drug classes for which lactate had the highest utility were salicylates, sympathomimetics, acetaminophen, and opioids (all area under the curve ≥0.97); lowest utility was for diuretics and angiotensin-converting enzyme inhibitors.

Conclusion: Initial lactate concentration is a useful biomarker for early clinical decisionmaking in ED patients with acute drug overdose. Studies of lactate-tailored management for these patient populations are warranted.

Figure 1. ROC Curve for Prediction of Drug Overdose Fatality using The Initial ED Lactate Concentration

This figure demonstrates the ROC curve of initial ED serum lactate concentration to predict in-hospital mortality. The AUC of 0.85 was statistically and clinically significant. The cutpoint that maximized the sum of sensitivity and specificity was ≥5.0 mmol/L (arrow). *Optimal cutpoint ≥5 mmol/L based on Youden Index. **Cutpoint <2.5 mmol/L had 99.5% NPV. Abbreviations: AUC = area under the curve; CI = confidence intervals; ED = emergency department: OCP = optimal cutpoint; ROC = receiver operating characteristics.