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The next lab value were going to talk about is lactic acid, also referred to as lactate. I’ve mentioned it previously in the metabolic acidosis, but I want to provide a little bit more detail and clarity as to what this lab value really means.
First let’s just look at normal values. In a perfectly healthy patient we expect their lactic acid level to be less than 1 mmol/L. There’s really no such thing as a “low” lactic acid level. In critically ill patient, we have a little bit more leeway because we expect their value to go up slightly. But as long as they are less than 2, we consider that normal in a critically ill patient.
To give you a little bit of foundation for where lactic acid comes from, I want to go all the way back to chemistry. The main source of lactic acid production in our body is anaerobic metabolism. Anaerobic means that cells are functioning and using energy without the presence of sufficient oxygen. So what happens in the absence of oxygen is that glucose gets broken down into pyruvate, which then gets broken down again into either alcohol and CO2 or lactic acid. So anytime we force ourselves to function without enough oxygen, we are going to end up with a buildup of lactic acid. So let’s look at what some of those conditions could be.
We will actually see that strenuous exercise, especially for a prolonged period of time, can cause a slight buildup of lactic acid. Some personal trainers will even tell you that you aren’t working hard enough if your muscles don’t burn because of the lactic acid. The good news is this is typically temporary and under normal circumstances would not cause any harmful effects. We could also see Anaerobic metabolism happening simply because of a lack of oxygen in the blood for whatever reason. the other thing that could cause a buildup of lactic acid is any state of poor perfusion to the tissues. The best examples of this are severe hypotension and shock states. We may have plenty of oxygen but we aren’t getting it, therefore the tissues are having the function without it. We also see an increase in lactic acid levels in sepsis or severe infection. This has been shown to be related to the release of catecholamines like epinephrine when the body is trying to fight off the infection. These two categories here, poor perfusion, and kept this, are the two most common causes of a lactic acidosis. Evaluating and trending lactic acid levels is now included in shock bundles and the surviving sepsis campaign guidelines. And, since the kidneys play a role in excreting lactic acid from our system, it’s possible that levels could be elevated in renal failure.
So, what will we see? First thing to understand is that elevated lactic acid levels, especially above about 4 mmol/L IS considered a Metabolic Acidosis. So, If you remember from the metabolic acidosis lesson, though most common sign of severe acidosis is vomiting. The body is trying desperately to get rid of acid anyway it knows how. one of those ways is also to breathe faster, so we will see tachypnea as well. The possible hyperkalemia, as well as the lactic acid itself, can cause muscle weakness, and the acidosis will mess with the super sensitive brain and cause altered levels of consciousness.
When it comes to lactic acidosis, our top priority is still to treat the cause. This might mean giving IV antibiotics for sepsis situation, giving vasopressors for a shock state, or making sure that we have Airway and breathing and oxygen support, so that the body can stop using anaerobic metabolism. Other interventions that we commonly use for lactic acidosis are IV fluid resuscitation, dialysis, and giving sodium bicarbonate. Fluid resuscitation tends to improve perfusion to the tissues to help decrease the need for anaerobic metabolism, but it will also help to dilute some of the acidity within the blood. Dialysis will help to remove excess lactic acid especially if Renal failure was part of the problem. Now, the administration of sodium bicarbonate for lactic acidosis specifically can be a little bit controversial. In certain patients it can actually cause an increase in acidosis. So just make sure that you are having a conversation with your provider about what’s best for your specific patient. Either way, sodium bicarbonate is not typically used alone when treating lactic acidosis. Usually we will add it to the other therapies.
Since I mentioned the surviving sepsis campaign, I want to make sure you know what the guidelines are when it comes to lactic acidosis and sepsis. Any lactic acid level greater than 2 is considered to be indicative of a septic situation. And, we will usually recheck the lactic acid 2 hours after the initial value to see what the trend is. Make sure you check your facility’s specific policies for details on how often to recheck.
Priority nursing concepts for a patient with elevated lactic acid levels would be acid-base balance, of course, as well as confusion and infection control because we know that poor perfusion and Pectus are the two most common causes of lactic acidosis.
Let’s recap. Lactic acidosis is the most common form of metabolic acidosis, especially in hospitalized or critically ill patients. Therefore, the symptoms you will see are related to the presence of metabolic acidosis. Things that can cause elevated lactic acid levels are anaerobic states like strenuous exercise, hypoxemia, or ischemia, poor perfusion like hypotension or shock, and sepsis or severe infection. That lactic acid gets released because of the catecholamine process. And any level greater than two in the presence of infection is considered indicative of sepsis. We always want to treat the cause and support airway and breathing as needed. We’ll give IV fluid resuscitation, IV antibiotics if necessary, and vasopressors to support appropriate perfusion.
So, those are the basics of the lactic acid level and what it means. Make sure you check out all the resources attached to this lesson. Now, go out and be your best selves today. And, as always, happy nursing!!