Prognostic Factors in Emergency Department Patients with Glyphosate Surfactant Intoxication: Point-of-Care Lactate Testing

An increasing number of suicide attempts involve the ingestion of glyphosate surfactant; hence, clinical toxicologists may encounter severe cases of glyphosate surfactant intoxication. In several other clinical conditions, serum lactate is used to predict outcome. We investigated the relationship between lactate levels and 30-day mortality from glyphosate surfactant poisoning. This retrospective analysis involved 232 patients who were admitted to the emergency department after acute glyphosate surfactant poisoning between January 2004 and June 2014. We used a receiver operating characteristic (ROC) curve to define the optimal cut-off point for lactate levels. A Kaplan-Meier 30-day survival curve was then analysed in terms of the defined cut-off level. We used multi-variate Cox proportional hazards regression analysis to determine the risk factors for 30-day mortality. Of the 232 patients, 29 died, yielding a case fatality rate of 12.5%. Lactate was significantly higher in non-survivors (6.5 +/- 3.1 mmol/L) than in survivors (3.3 +/- 2.2 mmol/L; p < 0.001), and elevated lactate was significantly associated with 30-day mortality. The area under the ROC curve of lactate levels was 0.836 [95% confidence interval (CI): 0.716-0.869]. Lactate levels higher than 4.7 mmol/L were associated with increased mortality in multi-variable analysis (hazard ratio: 3.2; 95% CI: 1.1-8.7). Besides lactate, age >59 years, corrected QT interval >495 ms and potassium >5.5 mmol/L were independent risk factors for 30-day mortality. Lactate is an independent predictor of 30-day mortality in patients with glyphosate surfactant poisoning. Early measurement of lactate levels may be a simple and practical way to assess the severity of intoxication.