UMEM Educational Pearls

Bottom Line: Lactate is a useful but imperfect marker of critical illness. Below are some key points to consider when interpreting lactate.

1. Lactated ringers should generally not significantly increase your measured lactate unless there is poor clearance (liver injury).
2. Many medications can cause an elevation in lactate through multiple mechanisms that do not improve with fluid resuscitation.
3. Lactate should be interpreted within the company it keeps (history, exam, vitals, urine output, hemodynamics).

Additional Information

Lactate is one of the most commonly used lab markers used in the emergency department to identify critically ill patients. However, the lactate is often used in isolation which leads to potentially excessive fluid administration (previously identified by cited physicians as the “Lacto-Bolo reflex”). Some studies have demonstrated signal towards harm in excessive fluid resuscitation. Additionally, an elevated lactate can sometimes be representative of an etiology that requires alternative treatment to fluids (mesenteric or limb ischemia, severe anemia, and others). Therefore, it is important to use the lactate in context with other clinical data (vitals, urine output, hemodynamics, etc) to determine need for fluid resuscitation.

Below are some common pitfalls with lactate management to consider on your next shift:

“I can't give Lactated Ringer's solution if I'm measuring lactates!?”

The human body makes 20 mmol/kg/day of lactate under normal conditions. A liter of lactated ringers contains 28 mmol/liter of lactate. This means three liters of lactated ringer's would be only about 5% of normal lactate in a 70 kg person. With normal clearance this is unlikely to have a clinically significant effect unless there is issue with clearance (liver injury). This was demonstrated in a study by Zitek et al that showed lactated ringer's and normal saline boluses had similar effects on lactate concentration.

"Medications rarely cause lactate elevation"

While lactate elevations are often ascribed to anaerobic metabolism (leading to pyruvate being metabolized into lactate), there are other mechanisms through which lactate elevation occurs including (with a few associated medications):

• Increased sympathetic stimulation (leads to excess pyruvate, causing lactate elevation) - albuterol, epinephrine, sympathomimetics
• Increased NADH/NAD ratio - ethanol, toxic alcohols
• Blockage of electron transport chain in mitochondria (prevents aerobic metabolism) - metformin, propofol (esp with propofol related infusion syndrome)

While lactate is a useful screening marker, it is not helpful in isolation alone and requires trending as well as clinical context. So next time you see an elevated lactate, think BEFORE you bolus.

References

1. Spiegel R, Gordon D, Marik PE. The origins of the Lacto-Bolo reflex: the mythology of lactate in sepsis. J Thorac Dis. 2020 Feb;12(Suppl 1):S48-S53.
2. Wardi G, Brice J, Correia M, Liu D, Self M, Tainter C. Demystifying Lactate in the Emergency Department. Ann Emerg Med. 2020 Feb;75(2):287-298. doi: 10.1016/j.annemergmed.2019.06.027. Epub 2019 Aug 29. Erratum in: Ann Emerg Med. 2020 Apr;75(4):557.
3. Garcia-Alvarez M, Marik P, Bellomo R. Sepsis-associated hyperlactatemia. Crit Care. 2014 Sep 9;18(5):503.
4. Zitek T, Skaggs ZD, Rahbar A, Patel J, Khan M. Does Intravenous Lactated Ringer's Solution Raise Serum Lactate? J Emerg Med. 2018 Sep;55(3):313-318.