Lab Values, part 5: Magnesium (Mg)

Hi, I'm Meris, and in this video, I'm going to be talking to you about the lab value magnesium along with its function, the expected range in the body, and the possible causes and symptoms of hypo and hypermagnesemia. I'm going to be following along using our lab values flashcards. These are available on our website, leveluprn.com, if you want to grab a set for yourself. Or if you are more of a fan of digital products, I would invite you to check out Flashables, the digital version of all of our flashcards available at your fingertips at all times. All right. Let's go ahead and get started.

So first up, what is magnesium? Why do we care about it? Magnesium is a really important electrolyte for our body for many biochemical reasons. However, the one that I always think of the most is for the nerve and muscle function, especially how these two things function together, and the place that we see this most commonly is in the deep tendon reflexes, and we're going to talk about that with hyper and hypomag. Now, what is the expected range for magnesium? The expected range for mag is going to be 1.3 to 2.1 milliequivalents per liter, or MEQ's per liter. This is a very small number and it's a very narrow range, so this is a tricky one because you've got to know that if I'm talking about a magnesium of 1, that's low, okay? And if I'm talking about a magnesium of 2.3, that's high. So we have to be on the same page about the expected range, and when we're talking about a narrow window like that, it's really important that you know that range backwards and forwards. And good news, we do have a cool chicken hint here to help remind you. MG's, which is how we abbreviate magnesium, but it's also a type of car. MG's are very small British cars. You can only fit one to two people in them. So this helps you to remember that the expected range for MAG MG is going to be around 1 to 2. It is your responsibility to remember the exact specific numbers, but that will help to get you at least closer to the value.

All right. Now, what if I have a magnesium level less than 1.3 MEQ's per liter? Then your patient is what we call hypomagnesemic, hypomagnesemic. And this is one of those electrolyte values that is crucially important to understand for clinical practice and just for the test-taking environment. This will have really important ramifications for you if you can apply it to the clinical and test-taking environment. Hypomag. Now, some possible causes here would be GI losses, especially related to diarrhea. So we're talking about GI losses out the back end, not the front end, right? Diuretics, because again, if I am using a diuretic, I can drop any of my electrolytes depending on which diuretic it is. Malnutrition and alcohol abuse, and I want you to kind of link those two things in your mind. Not all patients who are malnourished have alcohol use disorder, but most patients who have alcohol use disorder are also malnourished. So when you think alcohol abuse or alcohol use disorder, I need you to think this person is not meeting their nutritional needs very well for a variety of reasons that are for a different video but just link those two things together.

Now, what are some symptoms? Well, if my nerves and muscles aren't working right, a big affected muscle could be my heart. So dysrhythmias are definitely on the menu. Big one here being torsades de pointes, and torsades is a very specific cardiac rhythm. It's rare, but you know it when you see it. And it's because the electrical signal for the heart, it's spinning around the heart, and it's creating this very characteristic wave. Hypomagnesemia can lead to torsades, but it is also possible to go into torsades without being hypomagnesemic. I just want you to hear that. The reason I say this is because oftentimes the treatment for torsades is giving magnesium, and that is the case even if your patient does not have hypomag, okay, but it is linked with that. Another possible dysrhythmia would be just tachycardia. Tachycardia is a dysrhythmia, and that is possibly going to be seen in your patient as well.

Now, hypertension is possible, along with tremors and seizures and increased deep tendon reflexes. Magnesium has this inverse relationship. As magnesium rises, DTR's go down. As magnesium falls, DTR's go up, okay? So hypomagnesemic patients will have increased deep tendon reflexes, meaning you check my patella, and it just flies off that bed, kicks you in the face. We're talking about a really significant increase in that baseline DTR. Now, why does this matter? Well, because what happens if I'm hypermagnesemic? Great question. I'm so glad you asked. If I am hypermagnesemic, I have too much magnesium in my blood. This could be as a result of kidney disease. It could also be as a result of taking laxatives that contain magnesium. Magnesium containing laxatives, you're taking them, I'm adding magnesium to my body. I could end up with an imbalance.

Now, the symptoms here are kind of just going to be flipped, right? I'm going to have hypotension. I'm going to have lethargy and muscle weakness, decreased deep tendon reflexes, and going hand in hand with decreased DTR's is decreased respiratory drive. It is possible that your patient will experience respiratory depression if they are hypermagnesemic. They can also experience dysrhythmias up to and including cardiac arrest. Magnesium is super-duper important. The reason I mentioned this DTR thing and the breathing thing is because I give magnesium all the time in the ER setting, and it's a very different kind of a dosage and a timing schedule than when magnesium is given in labor and delivery. In labor and delivery, they are bolusing patients with large amounts of magnesium for different problems that they're trying to treat. Go look at the maternity playlist if you want more info on that. But that means that they need to be super-duper on the lookout for respiratory depression. My priority system here, if I'm giving magnesium or if I know my patient has too much magnesium, I'm concerned about their respiratory status. If we have that significant muscle weakness, the big muscle I need to breathe is my diaphragm, and if you make that weak, you're going to give me respiratory depression. So this is why when I give mag, it's less of a concern because it's not the same amount and it's not so quickly, but I still am concerned about that respiratory status. And in labor and delivery, when they are giving magnesium through the IV, they will be prioritizing that respiratory system when they're assessing, but furthermore, they're going to be assessing the deep tendon reflexes. If they see those deep tendon reflexes fall, fall, fall, and become absent, we have a problem, and that is a way for us to have that monitoring. So that is kind of your primer on magnesium, what it is, and how it works.

I'm so glad you stayed until the end because I'm going to test your knowledge of key facts provided in this video with my quiz questions.

When caring for a patient receiving an infusion of magnesium, which body system is the priority to assess?

Respiratory, due to the risk of respiratory depression with hypermagnesemia.

The nurse is caring for a patient who develops torsades de pointes. Which electrolyte imbalance should the nurse suspect?

Hypomagnesemia.

All right. That is it for this video. I hope you learned something and found it useful. All right. I'll see you in the next one. Thanks so much and happy studying.