ED Use of Rapid Lactate to Evaluate Patients With Acute Chest Pain

Abstract

Study objective: To test the hypothesis that ED arrival venous lactate levels can be used to diagnose acute myocardial infarction (AMI) and to identify patients with critical illness in the triage of ED patients presenting with chest pain. Methods: This was a prospective, double-blind, clinical study in an urban, academic ED. We enrolled a convenience sample of adult patients who had chest pain or cardiac symptoms suggesting AMI that began within 24 hours of presentation. Patients underwent standard medical management for their chest pain. Venous lactate samples were analyzed in the ED on whole blood. An abnormal lactate level of 1.5 mmol/L or higher at the time of arrival was prospectively defined as indicating the presence of acute cardiac disease. ECG findings, levels of creatine phosphokinase (CK) and CK-MB, hospital stay data, and diagnosis of AMI by the cardiology admitting team were recorded. Results: Of the 129 patients included in the study, 73 had an initial lactate level of 1.5 mmol/L or higher. The mean lactate level (±SD) for all patients was 1.8±1.2 mmol/L. A total of 28 patients (21%) were diagnosed with AMI and had a mean lactate level of 2.2±.7 mmol/L, compared with 1.7±1.3 mmol/L in those patients who were not diagnosed with AMI ( P<.03). The sensitivity of this lactate level in diagnosing AMI was 96% (95% confidence interval [CI], 89% to 100%), and the specificity was 55% (95% CI, 45% to 64%). The negative predictive value of blood lactate was 98% (95% CI, 95% to 100%). Lactate was elevated independent of the duration of chest pain symptoms, with a median time from onset to sampling of 3 hours. Lactate was elevated in patients who either died or required longer than 48 hours of ICU care, compared with survivors not requiring ICU care (4.5±4.3 mmol/L versus 1.4±.6 mmol/L, respectively; P<.01). Conclusion: The blood lactate concentration obtained on ED arrival identifies those chest pain patients with critical cardiac illness (eg, AMI, severe congestive heart failure [CHF], decompensated arrhythmias). A normal blood lactate result has a high negative predictive value for AMI. An elevated lactate level used in conjunction with ECG and history distinguishes patients with significant myocardium at risk who are likely to benefit from more urgent attention and interventions by the attending physician. Additionally, hyperlactatemia clearly correlates with mortality and the need for ICU management in the acute cardiac patient presenting to the ED. [Schmiechen NJ, Han C, Milzman DP: ED use of rapid lactate to evaluate patients with acute chest pain. Ann Emerg Med November 1997;30:571-577.]