Is There a Link?
Tobias AZ, Guyette FX, Seymour CW, et al. Pre-resuscitation lactate and hospital mortality in prehospital patients. Prehosp Emerg Care. Feb. 18, 2014. [Epub ahead of print.]
Serum lactate is a specific blood test used to determine metabolic acidosis and systemic anaerobic metabolism. Lactate is generally classified as normal when below 2 mmol/L, and is routinely used as part of trauma and sepsis panels in the ED. Although its validity and accuracy have come into question, measuring lactate still remains a viable, scientifically backed test.
We’ve previously reviewed the use of serum lactate as a predictor of mortality in the out-of-hospital setting, but many times there are confounding factors of the exam, such as the initiation of treatment before the testing of lactate. Dr. Adam Tobias and his associates from the University of Pittsburgh School of Medicine set out to determine if a prehospital lactate measurement of greater than 2.0 mmol/L before the initiation of treatment, such as fluid resuscitation, is a reliable indicator of in-hospital mortality in the non-trauma patient.
Urban rural and suburban ALS providers in the greater Pittsburgh area attended a one-hour training class on the use of the LactatePro analyzer (the only FDA-approved lactate analyzer currently available) prior to implementation. A convenience study was performed on patients transported to tertiary receiving facilities in the Pittsburgh area who met the authors’ criteria of being critically ill, such as those presenting with an altered mental status, hypotension, tachycardia or abnormal respirations. Patients who met the criteria also required IV access, and the lactate analysis was performed on blood obtained from starting the IV.
Of 876 patients meeting the criteria, 673 (77%) were included in the final statistical evaluation with 160 (18%) patients being excluded for traumatic injuries, 37 (4%) patients being excluded for missing data, and six (1%) excluded for lack of documented point of care lactate value.
Of the 673 evaluated, 307 (46%) had a lactate value greater than or equal to 2.0 mmol/L compared to 366 (54%) with a lactate less than 2.0 mmol/L. Chest pain and shortness of breath were the most likely complaint in each group, average scene times were standard in both groups at approximately 35 minutes, and vital signs were also approximately the same, with patients in the elevated lactate group more likely to be hypotensive. ICU admission and in-hospital death nearly double in the elevated lactate group. Final evaluation with other statistical factors calculated in shows that a lactate of greater than or equal to 2.0 mmol/L had a modest sensitivity at 76% but a low specificity at 55% for likelihood of in-hospital mortality. Although compared with other tracked factors such as hypotension, respiratory rate, heart rate, or GCS; lactate was the most likely predictor of in-hospital mortality when measured by prehospital providers.
This is the third paper we've seen in recent years assessing the validity of prehospital lactate measurement by point-of-care test. The results seem to be the same, with neither the authors nor the evaluators being completely sold that this is a perfect test. Interestingly, this paper actually combines abnormal vital signs with lactate. When combined, they seem to form a better test; but even the authors admit that perhaps a better biomarker should be sought out. We’re big fans of adding tools to the toolbox of prehospital providers; however measuring lactate doesn’t seem to be a test that’s quite there yet. We look forward to a future when point-of-care lactate monitors are more readily available; however, we need to keep in mind that clinical judgment abnormal vital signs have proven time and time again to be reliable indicators of critical illness and injury.
We’d also like to thank Dr. Tobias and his group for their diligence in evaluating the use of prehospital lactate measurements.