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Demystifying Lactate in the Emergency Department

March 6, 2020

Written by Bo Stubblefield

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Lactate is a frequently ordered biomarker in the Emergency Department. This is a large review elucidating the diagnostic and prognostic interpretation of lactate in the ED.

Why does this matter?
It may be hubris to think that we understand the ins and outs of every biomarker ordered in the Emergency Department. As the title of this article suggests, lactate is one of these biomarkers that often generates more questions than answers. This piece by Wardi, et al. dispels myths, addresses the physiology, homeostasis, and metabolism of lactate, and delineates the utility of lactate between various conditions. How should we be using lactate as a prognostic or diagnostic tool in the Emergency Department?

The tale of lactate: From sour milk isolate to the biomarker we love to hate

Background:

Lactate is an organic acid that is principally found in its ionized form at physiologic pH. Traditionally, it has been viewed as an end product of anaerobic metabolism, but more contemporary understanding recognizes lactate as a key player in energy use even under aerobic conditions. The liver metabolizes 75%. Kidneys metabolize 25%.

This is a large review article, so here are the high points:

Myths…

  • Tourniquet Use – application of a venous tourniquet does not significantly alter venous lactate levels.

  • Arterial v. Venous Lactate –  there are mild discrepancies with hyperlactatemia. Arterial and central blood samples represent lactate that is systemically circulated, whereas venous samples reflect the local milieu.

  • Effect of LR Solution on Serum Lactate – There is no published evidence that a bolus of LR significantly increases lactate compared to NS, although transient elevations may be observed.

Lactate &…

  • Lactate & Sepsis –  The specific anatomic site of lactate generation in septic patients remains controversial as does the mechanistic reasoning behind hyperlactatemia in sepsis. It cannot be fully explained by tissue hypoxia and resultant anaerobic metabolism but continues to serve as a marker for risk stratification and predictor of mortality.

  • Lactate & Trauma, Burns, Inhalational Injuries – As with sepsis, lactate serves as a prognostic indicator of resuscitation, as well as infectious complications, organ dysfunction, and mortality.

  • Lactate & Seizures – hyperlactemia is known to be caused by local muscle tissue hypoxia. If caused solely by seizure, it should have rapid clearance within 1-2 hours. There is no correlation between degree of lactate elevation and outcome.

  • Lactate & Toxins/Medications – This is a large chunk of the paper, and there is a table provided which includes mechanisms and recommended therapy. It is worth a look.

Recap:

The diagnostic utility of lactate in the ED is diverse. Elevated levels may be the result of overproduction, impaired elimination, or both. Regardless, an elevated lactate is associated with a worse prognosis in many conditions. Measurement of lactate can be a useful tool in the ED, and a nuanced understanding of lactate levels can help guide us toward appropriate interventions.

Another Spoonful

Source
Demystifying Lactate in the Emergency Department. Ann Emerg Med. 2019 Aug 29. pii: S0196-0644(19)30537-2. doi: 10.1016/j.annemergmed.2019.06.027.

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Reviewed by Clay Smith

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