Brain Natriuretic Peptide (BNP) Lab Values

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In this lesson we're going to talk about brain natriuretic peptide, or BNP. BNP ... Let's pretend this is a heart here. This is our little heart diagram. BNP is released from the ventricles of the heart when the ventricles are stretched. So under conditions that cause stretch in the ventricles, we're going to have BNP released. What are some conditions that cause stretch? Well, the main one we're looking for here is congestive heart failure, or CHF.

The normal value for BNP is under 100. We want it to be under 100. 100 to 300 would be low level heart failure going on. Over 300 would be moderate, and then over 900 would be severe heart failure. Now I've seen levels go as high as like 4500 in patients who have very extreme heart failure. So it's really something we're looking for and we're watching for in these types of patients.

Now it's used to test the likely diagnosis of heart failure. So when we see these levels, we're saying, "Okay, it's really likely that this patient has heart failure." But we want to make sure we're checking with other symptoms with these patients. We're looking for symptoms. We're looking for other tests, doing x-rays and things like that that we'll talk about in a minute. But it's going to give us the likely diagnosis of heart failure. And, again, the higher the result ... The highest I've seen, again, like is 4500. The more likely the diagnosis of heart failure for this patient.

So in a normal heart, increased volume ... So we have more volume coming into the system. This increased volume will cause increased ventricular stretch. Now what happens in this case is BNP is then released. So as the ventricles stretch, BNP is released. What BNP does is it promotes the excretion of sodium in urine, which is called natriuresis.

So as BNP is released, it causes the excretion of sodium in urine, which is natriuresis, which also leads to the excretion of water. So we're getting rid of some of that volume to decrease that stretch. Now what that then leads to is it leads to this decreased intravascular volume, and that leads to a decreased workload on the heart, which then improves our cardiac function. So that's why we need BNP, and that's the role it plays in our normal functioning heart.

But if the heart can't pump because of a weakness, for example, heart failure or pump failure. If our pump is not working, BNP keeps being released. The heart starts freaking out. It says, "Hey, I really got to get rid of all of this volume. Please help get this out. Here's all this BNP. Start working, start working." And that lab value continues to climb as our ventricles continue to stretch because of the pump failure in heart failure. All right?

So here's a couple things you need to keep in mind. When we run this lab value, we're using our lavender top tube, which is the EDTA tube. You might also see requested an NT-proBNP to help further diagnose. You're going to want to give this in the serum separator tube, which is the tiger top. If you've seen it, you'll recognize this top. But most important, keep in mind this is going to be in a lavender top tube generally as you're running this lab.

So let's look at the elevated levels, how we're going to treat it, and how we're going to further diagnose this. So in our heart, any time these ventricles stretch, we're going to have this release of BNP to try to help get rid of this fluid volume. A normal lab value for someone with a functioning heart would be less than 100. That shows that the heart is functioning normally. BNP is doing what it should do, and everything is working as it should. As the level starts to increase over 100, we start to say that heart failure is likely. The more that BNP increases, the more likely it is that we're going to get a diagnosis of heart failure.

Other things that we're going to want to do as we evaluate this patient is we're going to have radiology come in and check for things like pulmonary edema, which is the result of this heart failure. That fluid is looking for a place to go. It's going to be harder and harder for our patients to breathe as a result of that pulmonary edema. We can also do an echocardiogram to get a nice picture of the heart and what's actually going on.

So how are we going to treat this? Here's our heart. Here's our aorta. We got these ventricles just full of fluid that we can't get rid of. Our BNP is continuing to climb. So remember, we're not really treating the BNP. What we're trying to treat is the heart. And as we treat that heart, the BNP should start to decrease. So the first thing we want to do is we want to increase and improve our contractility.

What is the contractility? Contractility is really the squeeze of these ventricles. If you think of a sponge, as you squeeze that sponge, that's like the contractility. In a patient with heart failure, you're not getting a lot of squeeze, so we want to improve that squeeze. The kind of medications we could give for that would be like sympathomimetics. And you want to look at the cheat sheet on hemodynamics, because we really work through this chart of what you would do in different cases of heart function. So sympathomimetics are going to help improve that squeeze, which is going to help get some of that fluid out.

We then want to also, of course, decrease our fluid volume. That's what the problem is here. BNP is going out trying to say, "Hey, let's get this volume down through natriuresis," but the heart isn't able to get rid of that volume. So we want to try to decrease that volume. Some things we can do with that are we can give like diuretics, or we can give ARBs.

Then, of course, we want to decrease systemic vascular resistance. Systemic vascular resistance is the pressure that these ventricles have to squeeze in order to open this aortic valve and get this fluid out. To open that aortic valve, that value is the systemic vascular resistance, essentially our blood pressure. The types of meds we want to give for that would be vasodilators. So if we open this vessel up and make it less difficult to squeeze and expand, we're going to see hopefully more of that fluid come out. We can also give ACE inhibitors. So for these, we can give vasodilators or ACE inhibitors.

Then, of course, guys, we want to watch our patient for signs and symptoms of heart failure to make sure they're consistent with these lab results. Is the patient having a hard time breathing? What's their fluid volume looking like? Do they have edema? And we really want to look for those things.

Now some nursing concepts we're going to look at, of course, are lab values. We've added lab values in here so that you can find all the lab values you need. And then you're going to be looking at perfusion, of course. Is the patient getting blood, perfusing the way that they need to for the body to be healthy.
So let's do a key points. Let's do a quick overview really quick here. BNP normal lab value is 100. Anything greater, there's a high likelihood of heart failure. As that level climbs, there's a higher likelihood. What happens during ventricular stretch, BNP is released to try to help get rid of some of this volume. In a patient that has heart failure, that doesn't matter. It doesn't matter how much BNP comes out, we're not going to be able to get rid of all that volume.

So what BNP does to try to help with this is BNP pushes sodium out. Water follows sodium, so we're getting rid of all that extra volume. With our broken pump, the heart cannot keep up with these demands, and BNP stays high or it continues to grow, as none of that volume is able to come off.

All right, so that's really BNP in a nutshell, guys. I hope that helps. And, as always, happy nursing.
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