If there’s one thing that will separate the rookie nurse from the seasoned pro is how an elevated lactate is interpreted. The gut reaction in many cases is to scream SEPSIS from the rooftops. After all, sepsis is very serious and catching it early plays an enormous role in reducing mortality. And yes, one of the signs of sepsis IS an elevated lactate. However, loads of other things can cause it to be high, and knowing what these are will not only make you come across as incredibly competent, you’ll be prepared to take even better care of your patients.
So, let’s go through some common reasons for it to be elevated and the WHY behind each one. But first…
What is lactate?
Lactate is, in general terms, a marker that anaerobic metabolism has occurred in the body. It is produced in most tissues, but mainly it’s found in muscle. In a healthy individual, it is cleared by the liver (and a little bit by the kidneys), so normal levels are typically < 1.0 mmol/L, and we start getting interested when it’s above 2-ish.
In NORMAL metabolism (aka AEROBIC metabolism), glycolysis produces pyruvate which then enters the Krebs cycle and lactate is NOT produced. However, in ANAEROBIC metabolism, the end result of glycolysis will be lactate.
In the most general terms possible, an elevated level is a consequence of either decreased clearance, increased production, or a combination of both.
How is it measured?
There are two ways to measure lactate in the clinical setting. You can draw venous or arterial blood (the latter would be from your arterial line if you have one), put it on ice and send it off to the lab. Or, you can obtain a reading from an ABG, which your respiratory therapist will provide for you.
Some reasons for it to be elevated
Sepsis: Traditional thinking blames an elevated lactate on simple tissue hypoxia (think of that low BP leading to low perfusion leading to global hypoxia of cells). However, some newer studies are indicating that an elevated lactate in sepsis is due, largely, to stimulation of beta-2 adrenergic receptors. The super-short version is that the stimulation of these receptors up-regulates the process of glycolysis which generates increased amounts of pyruvate. This pyruvate can be used by the cell’s mitochondria thanks to the Krebs cycle…and excess pyruvate is converted into…guess what? Lactate. Whether the cause of the anaerobic metabolism is due to beta-2 adrenergic receptors or simply just hypoperfusion is still being studied…but it’s an interesting concept. The takeaway is that lactate is a product of anaerobic metabolism in the tissues that are not being perfused.
Shock States: While sepsis is distributive shock, note that other types of shock can lead to an elevated level…cardiogenic shock, hypovolemic shock, and obstructive shock are all guilty.
Cardiac Arrest: If your patient suffered a cardiac arrest, expect lactate levels to be elevated due to tissue ischemia. How quickly the patient clears this lactate is being studied as an indicator of survival. A recent study indicated that post-arrest patients with an initial lactate > 5 mmol/L had a 39% mortality rate, and patients with a lactate > 10 mmol/L had a mortality rate as high as 92%.
Liver Disease: Recall that lactate is cleared by the liver, so if your patient has liver disease, you’ll probably see an elevated lactate. This doesn’t mean the patient is septic, it’s just that the liver isn’t clearing the lactate as quickly or efficiently as it would in a healthy patient. So, for example. Let’s say your patient has liver disease AND had a cardiac arrest. The normal elevation of lactate is going to stick around for much longer in your liver disease patient…doesn’t mean they’re septic, but it certainly means they’re sick.
Seizures: During seizures, the muscles don’t get the oxygen they need for such intense activity…thus the result is an elevated lactate. It is important to note that this elevation is typically transient and resolves on its own. However, if your patient’s level remains high more than a couple hours after the seizure, then something else is probably going on.
Asthma: High dose albuterol (a beta-2 adrenergic) can cause an elevated lactate. Also, it is suggested that the severity of the asthma attack can be correlated to lactate levels. In addition, the excessive muscle use associated with asthma can, when combined with respiratory fatigue, lead to an elevated level.
Ischemic Tissue: Crush injury, burns and even leaving a tourniquet on too long before a blood draw can cause ischemia and an elevated level.
Trauma: Most traumas cause blood loss which leads to hypoperfusion, which leads to…elevated lactate. You’re getting the hang of this! Also, traumas often lead to compartment syndrome…and if you’ve read my post on this topic then you know it can lead to ischemia.
Bowel Dysfunction: Mesenteric ischemia typically causes an elevated lactate as can bacterial peritonitis and acute pancreatitis.
Medications: Several meds cause an elevation in lactate. A few of the most common are metformin, albuterol, epinephrine, zyvox and acetaminophen. The mechanism of action varies with each medication…but if your patient is on these meds or you suspect an overdose of these meds, you will likely see an elevation not related to sepsis.
Smoke Inhalation: If you’ve got a patient who’s been in a fire, they may have an elevated level due to the possibility of inhaling carbon monoxide and/or cyanide, both of which can lead to elevations. And, of course, the presence of burns would cause an elevation as well.
Alcoholism: Many of your ETOH patients will have a thiamine deficiency (as will malnourished patients…even patients who’ve had gastric bypass or who suffer from anorexia nervosa). However, ETOH is MUCH more common than either of these and one of the ways you treat these patients is with a thiamine infusion (you’ll be giving an IV bag called a “banana bag” that contains important electrolytes, vitamins and thiamine). Why is thiamine a big deal? Because without thiamine, the body uses anaerobic metabolism more so than aerobic metabolism, and the production of lactate goes up.
Cancer: Lactate levels are often increased in patients with lymphoma or leukemia, especially if the liver is affected. Studies suggest it has to do with malnutrition (thiamine deficiency), tumor expression of certain enzymes and mitochondrial dysfunction.
Ok..whew! Every now and then I have a blog post idea that starts out simple and becomes a beast…this was one of those times! I hope this helps you understand all the reasons lactate can be elevated. Of course, take the whole clinical picture into account when making your recommendations, but this list is a good place to start.
Got questions about other lab values? Let us know in the comments below!