Anion Gap: Principles and Clinical Use in DKA Management (Nursing)

00:00 Now let's take a look at that anion gap. Now we definitely want a serum electrical neutrality.

00:06 That's what we're looking for, right? All of our positive charges, cations, have to balance out with our negative charges, anions. So when we talk about serum electrical neutrality, that means we just want to balance. We want the positive charges to be balanced with the negative charges. We call positive charges cations, we call negative charges anions. So positive charged cations, the one you're going to see the most of is sodium, right? This is our biggest, most abundant positive charge cation. Potassium is also a positive charge cation, but it's in a much smaller amount. Now the negative charge anions are chloride. This is our biggest measured negative charge. So sodium is our biggest measured positive charge. Chloride is our biggest measured negative charge. And they also have bicarbonate, which is in our buffer system. That's another anion. And there's also some unmeasured anions, proteins and other things, but just know they're out there. But our biggest ones, you should be aware of sodium, potassium as positive charge cations, and chloride and bicarbonate as negative charge anions. Now there's this formula where you figure out the anion gap, right? That's telling us the difference in where we want to be, which is neutrality and where we are. So you're not going to have to memorize, I would imagine this formula, but I just want you to be aware of where we get it. So the anion gap, the difference between the neutrality is you take the patient's sodium plus their potassium, and you take their chloride plus their bicarb. Now what you do is take those two totals, and you subtract them from each other. So let's probably simplify it to something like sodium minus, you see that formula there. Don't get too caught up in that, but just know that the normal level for an anion gap is 3 to 10. And how do we get that? We take the total of those two positive cations and the two negative anions, and we subtract the negative anions from the positive cations.

02:09 And we want to be around 3 to 10. That's what we want the answer to be. If it's outside of that, then we have a problem. Okay, so you should be clear where do we get this anion gap? Well that represents the difference between our positive cations and our negative anions. We want the difference between if we subtract the negative anions from the positive to be between 3 and 10.

02:35 Now there's some tests that you can use that will help show an anion gap for you. You can use a basic metabolic panel, a comprehensive metabolic panel, an electrolyte panel, or even a renal function panel. Those are just names of groups of lab work, right? Because what we're looking for is levels of sodium, potassium, chloride, and bicarb so that we can calculate the anion gap. Now a high anion gap is greater than 20 in DKA. Remember what normal is, it's 3 to 10. That would tell us we're in a good place of balance. But in DKA, that's going to be greater than 20. So this usually means there's an excess acid in the blood. So a high anion gap greater than 20 in DKA is telling us, hey, there's likely an excess of acids in the blood. Now in the DKA state, these acids are known as ketones. Why are the ketones there? Because the client couldn't use glucose for energy. They didn't have the insulin to get it into the cell and out of their lab work. So it turns to fat for energy. When you break down fat for energy, a byproduct of that is ketones. And that's why someone in DKA will have a high anion gap, usually greater than 20, that'll let us know those acids are there because there's excessive ketones in the blood because the client has had to use fat for energy because they couldn't use the glucose. So how do you apply this as a nurse? Well, you can take a look at trends in the anion gap. You know, we always recommend lab work is always about the trends. You always compare multiple lab works to see what you're doing, what interventions are happening, how the patient is responding to the treatment. An anion gap is no exception. So you can use the trends in the anion gap to know if your DKA treatment is working. So you could see this on a test question. You're going to need to know what normal anion gap is. If you say the patient came in with an anion gap of 26, what would have to happen to that anion gap to know that your treatment is beginning to make a difference? Would the anion gap go higher than 26 or should it be going lower? Right? If you remember that normal is 3 to 10, you're going to know that your treatment is effective and it's working if that anion gap is getting lower, moving toward that level of 3 to 10. So if the gap is closing, it's getting lower, then the bio is able to clear out those ketones. If the gap isn't closing, even though you're doing treatment, something else might be wrong. This is why you would call the health care provider. You can put your heads together and figure out what is going wrong with this client. Now, these are red flags I don't want you to watch for. So all nurses should watch for these red flags, because if you have that increasing anion gap, here's some of the things that it could be causing that. DKA might be worsening instead of getting better.

05:20 Something might be wrong with the insulin infusion. You might think they're getting insulin, but maybe it's infiltrated or the insulin has been turned off, any number of things. But the first thing you want to do is check your insulin pump and make sure that's being delivered in a way that is appropriate and not infiltrated. Now, the last thing I want you to think about is there might be another source of acid, like maybe lactic acidosis if the patient went into shock.

05:45 Those are some really serious things. But if you don't see the appropriate change in the anion gap, you'll know that the DKA is likely worsening. You can check for causes for that. It might be because they're not receiving the insulin that you think they are, or there could be another source of acid like lactic acidosis that develops in shock. So how do you monitor this? How do you keep an idea of what's going on? Well, you make sure that you track the anion gap alongside your other labs. Know what the patient was when they came in and what's happened on the shift since then and what's going on in your shift. If it's trending down with treatment, that's good. If it's trending up, you've got a problem and you need to do some more investigation. Remember, if that gap isn't improving with the treatment that you're doing, you need to contact the healthcare provider.

06:33 The earlier, the better. So let's say if I have a client and they have a high anion gap and a low bicarb, that's going to be metabolic acidosis. An example would be DKA. Now, if they have a normal anion gap and a low bicarb, that might be something like the patient's experienced a loss of a lot of bicarb, like in diarrhea. So that's not a real pleasant example, but that gives you kind of an idea of how we use anion gap. You know what to look for in DKA. And I just gave you an example of, hey, what would happen if someone had pretty significant diarrhea? Well, they could have a normal anion gap, but they also have a low bicarb. So we can use the anion gap for all kinds of things.

07:14 But a quick tip for all bedside nurses, if you're caring for a DKA patient and one, the glucose is coming down, but the anion gap isn't closing and the patient isn't feeling better, keep in mind something else is likely going on and it's worth you calling the provider and having a discussion.

07:34 So next time you're taking care of a DKA patient, you see that glucose normalizing, but the anion gap isn't closing, isn't going back to normal, and the patient isn't feeling better, you need to contact the health care provider. So some key points I want you to remember about how to track the anion gap alongside the glucose. See, these two should improve together. The glucose should be coming down towards normal and the anion gap should be returning to a level between three to ten.

08:01 Because if that gap isn't closing, despite their glucose being better, being more normal, again, you've got to look for more problems. Remember, these patients can have multiple acid-based disorders at the same time. Now, it's not really fun, is it? It'd be nice if like on a test question, a patient will likely have just one disorder. But in real life, patients come to us with multiple disorders at the same time. Don't worry about that, except know if you keep an eye on your labs and your assessments and you know what should be happening, you'll be able to identify that earlier. So while you're tracking these alongside each other, the glucose and the anion gap, you know that they should improve together because you're using the trending of the anion gap so that you catch problems earlier. You won't be caught unaware when this patient codes. You're going to know like, oh, things were not going well, and you can do things to intervene because that anion gap is something that can help you identify when someone is getting sicker, when they're deteriorating, before the clinical symptoms become severe.