What is blood lactate? And what can altered levels be an indication of?
Lactate is a product of anaerobic metabolism - which is the result of cell metabolism in the absence of sufficient oxygen. Typically, lactate is metabolized by the liver to prevent toxic accumulation in the bloodstream (1). However, in the absence of adequate tissue perfusion, these levels can accumulate and have devastating effects on the body. “Normal lactate levels are less than 1.0 mmol/L in both arterial and venous blood[…] [and] one study showed a level above 4.0mmol/L was associated with a 27% mortality rate compared with 7% for patients with a lactate of 2.5-4.0 mmol/L2” (1). Conditions that can cause an increase in blood lactate levels include trauma, seizures, severe sepsis, or any condition in which the oxygen demand placed on the body cannot be met by tissue perfusion status. Currently, severe sepsis or septic shock is the condition researchers are most interested in treating and/or triaging by involving EMS in taking field lactate levels on patients.
How are lactate levels measured in the field?
In the hospital, blood lactate levels are measured via arterial or venous blood sampling, with arterial samples being the “gold” standard, and central venous sampling being a close second (2). However, in the field, we only have access to capillary or peripheral venous blood, which limits the equipment we can utilize to measure blood lactate in patients. Studies conducted to determine the effectiveness of measuring blood lactate in the field typically use a handheld lactate monitor. These monitors utilize capillary blood (although if IV access has been made, peripheral venous blood can also be measured) to analyze lactate levels, much like a blood glucose monitor would. Unfortunately, the research on the accuracy of these monitors is still somewhat inconclusive (3,4) with the general understanding that the closer a patient is to a “normal” blood lactate reading, the more accurate these handheld devices are, and the more extreme the measurement (typically if the reading is high) the more discrepancy there will be between the handheld monitor and a laboratory result obtained using central venous or arterial blood.
What are the potential benefits of measuring blood lactate in the field?
As noted earlier, blood lactate is critical in detecting septic patients. The swift management of sepsis is crucial in preserving life. Therefore, being able to detect these levels in the field and begin treatment, as well as notify the receiving hospital, as early as possible could have huge implications in the quality of overall patient care.
So far, research is once again divided on the usefulness of determining blood lactate in the field (5,6). However, this lack of agreement is based solely on EMS personnel’s ability to accurately measure blood lactate. Due to these varying degrees of accuracy, some studies have determined that early notification aids in both pre-hospital and emergency department treatment, while other studies show that the inaccurate measurements only serve to over- or under-triage patients, which ultimately causes unnecessary time delays in treatment.
Most agree that the ability of EMS personnel to accurately measure blood lactate in the field would tremendously benefit patients suffering from severe sepsis or septic shock, however, researchers still need to agree on the accuracy of tools used to measure those levels in an out-of-hospital setting.