How Do Beta Blockers Work? (Nursing)

00:01 Okay. Now this is to our friends the beta blockers. Look at this.

00:05 We got a football player out there. That's an American football player.

00:08 Think of him as like a linebacker blocker.

00:12 And so it's labetalol, propranolol, atenolol, metoprolol.

00:16 Those are all some of the olols examples to help you start to get the idea that that's one way you can remember what beta blockers are.

00:24 They end in that "olol" ending.

00:26 So, how do they work? Well, beta-adrenergic blockers is the same thing as a beta blocker.

00:33 We're talking about the receptor.

00:35 Remember, beta-adrenergic receptors, their job is to respond to sympathetic nervous system stimulation.

00:42 So, a beta blocker is a medication that fits into that receptor, but it blocks that response. So, if a patient is taking a beta- adrenergic blocker or beta blocker, for short, it's going to prevent the stimulation of that sympathetic nervous system and give us the action that we want.

01:01 See, it blocks the action of the catecholamines.

01:04 I know you've heard of these. Like, epinephrine, think of it like an adrenaline, norepinephrine is another catecholamine at these beta-adrenergic receptors.

01:13 Because in a healthy body, here's how it works.

01:15 So you're afraid -- something happens.

01:18 Your body kicks into high gear.

01:20 Your adrenal medulla -- squirts out these substances.

01:24 They race through your body, they hit the receptors on your heart.

01:27 They make it pump harder and faster.

01:29 That's what norepinephrine and epinephrine do.

01:32 But if I'm taking a beta blocker, then I've got a drug that's already comfy, all cuddled in on that beta receptor.

01:42 So, when those catecholamines get squirted out in my body, they race all around, but they cannot bind to the receptors on my heart.

01:50 So, therefore, my heart rate is lower, and it's not pumping as hard.

01:54 That's what beta blockers do.

01:57 They block that resection. They are medications that fit perfectly onto those beta receptors, and they block those receptors from being activated.

02:06 And receptors that are blocked means you'll get the opposite response. Now, in case I didn't make sense, we'll go into that again. So don't worry.

02:14 If it's just starting to settle in in your brain, I promise you, we'll get there.

02:18 See, beta 1 receptor sites are predominantly in the heart.

02:22 Norepinephrine and epinephrine are the substances that come out of the adrenal medulla, and here's what happens when they squirt out norepinephrine and epinephrine.

02:34 The SA node of the heart -- that's the pacemaker of your heart -- when those beta receptors receive epinephrine or norepinephrine, the SA node goes faster.

02:44 And the AV node and the Purkinje fibers, they also increase our conduction velocity.

02:48 So, what happens is the SA node's the pacemaker, goes, SA node, AV node, Purkinje fibers.

02:54 That's how a beat goes through the heart.

02:58 When you receive norepinephrine and epinephrine into those receptors -- it goes through faster. So, your heart rate is faster, and the atrial and the ventricular muscles increase in velocity and conductivity.

03:10 Well, those are a lot of words. All that means is, your heart is going to be faster and much stronger and harder, which is a good thing because if my sympathetic nervous system has been stimulated, I'm likely in danger.

03:25 There's a reason my body is perceiving that I'm going to need to run really fast. So I'm going to need oxygen, I'm gonna need that heart pumping fast, and I'm gonna need lungs that bronchodilate.

03:35 Now, bronchodilating is a job of the beta 2 receptors.

03:39 Now, an easy way that I remember this is that beta 1 receptors are on your heart, and I have 1 heart.

03:45 Beta 2 receptors are on my lungs, and I have 2 lungs.

03:49 So that's how I keep track of where beta 1 receptors are and where beta 2 receptors are.

03:54 So they get hit with epinephrine from the adrenal medulla.

03:57 And then what happens is the arterioles dilate in the heart, the lung, and the skeletal muscle.

04:02 Hey, that's cool, because the arterioles are like the control valves, so they're going to dilate when those messengers, epinephrine from the adrenal medulla, hits the beta 2 receptors, arterioles dilate.

04:16 Now, things are opening wide up. Those bronchi -- they're dilating because they know we need more oxygen, because we're going to need to run. Think of it as running.

04:25 The same response happens when you get stressed out, emotional, or mad, but just think of it as if you're going to need physical ability to run.

04:33 Now, the uterus relaxes. That may seem kind of odd, that we're talking about it right here, but let's think about it.

04:39 If I was trying to run away from something that was trying to kill me, I don't want to drop a baby here.

04:45 I also would want to relax my GI tract because I don't want to drop anything out here.

04:49 So what happens is my gut slows down, my uterus relaxes so it won't push out a baby. Now, what are the odds that this is going to be happening? Not really strong, right? That's just a funny way for you to remember sympathetic nervous system stimulation.

05:04 Arterioles, they dilate.

05:07 Bronchi dilate because I need more oxygen.

05:09 My uterus relaxes because I don't want to drop a kid.

05:12 And then glycogenolysis in the liver.

05:16 See, the body is so amazing.

05:18 It picks up that you need more energy, right? Because if I'm getting to -- trust me. If I'm going to run, I need a lot more energy.

05:26 So, glycogenolysis is your body's way of breaking out that stored glycogen into glucose.

05:33 So remember, when you have excess glucose in your blood, your body takes it in, stores it in 2 places. Your – predominantly, your liver and your skeletal muscle.

05:41 When your sympathetic nervous system is stimulated, it's amazing that your body knows, "Hey, break out the stored stuff." Glyco, right, genolysis, so "lysis," breaking apart.

05:53 "Glyco" standing for the sugar, and "gen," to create.

05:57 So that's what glycogenolysis means and it happens in your liver.

06:02 Okay. So you've got a good feel from this slide. That's a lot of information.

06:06 Let's go back over it to make sure it's solid in your mind.

06:09 On 1 side, we have the beta 1 receptor hearts.

06:12 On the other -- beta 1 receptor sites.

06:16 On the other slide, we have beta 2 receptor sites.

06:19 So make sure you have solid in your mind, beta 1 receptors are predominantly on your 1 heart.

06:26 Beta 2 receptors are predominantly in your, what? Good, bronchi blood vessels and uterus, which is not going to apply to a lot, but I want it to stick in your mind, anyway.

06:38 So, when I get the beta-adrenergic blockers, I'm going to look at impacting the jobs of these receptors in your body.

06:47 Okay. Now this chart is really going to be helpful, so just hang with us as we fill these in.

06:53 Now you'll notice it says "beta 1 receptor sites." Do you see that on the far side of your screen? The title of this is "Beta- adrenergic blockers block the activation of beta receptors!" Exclamation point, all right? So this is to give you context about what we're talking about.

07:10 In 1 column, we're going to talk about what happens at a beta 1 receptor site when it receives or it binds to norepinephrine or epinephrine, what the response is.

07:22 The next column will say what happens -- uh huh -- if you've given that patient a beta blocker? So the drug will beat those guys to the beta 1 receptor site.

07:32 So let's look at that again.

07:34 Okay, if a beta 1 receptor site binds to norepinephrine or epinephrine, the SA node increases the heart rate.

07:43 But if you've given them a beta blocker, then the heart rate increase is blocked and the heart rate will, therefore, decrease.

07:51 So that's an important point with beta blockers. Their heart rate will definitely be lower.

07:57 Now, let me tell you why this matters.

07:59 Back before I was able to make some lifestyle changes, I was on 5 or 6 blood pressure medications.

08:06 One of them was a beta blocker.

08:08 Beta blockers directly decrease your heart rate, so don't ever try to do physical training with an elevated heart rate when your patient's on a beta blocker.

08:19 So keep that in mind when you're teaching your patients, don't do physical activity trying to get your heart rate to a certain level.

08:25 It's going to be a big problem. You'll do some damage to your heart before someone on a high-dose beta blocker can ever get their heart rate up that high. Why? Because you've got the beta blocker drug on the beta 1 receptor, and the SA node cannot respond to the increased demand like it normally would because they're taking a beta blocker.

08:46 Now what happens at the AV node and the Purkinje fibers? Well, under normal conditions, when norepinephrine and epinephrine bind to that beta 1 receptor, the AV node -- remember that's the pacemaker -- SA node, AV node, Purkinje fibers -- You got all that going on.

09:02 AV node and Purkinje fibers, it'll increase their conduction velocity.

09:06 So those fires will -- those impulses will just be tearing through the heart at a much faster rate, unless they have a beta blocker on board.

09:17 Then that increase in velocity, that normally happens when norepinephrine and epinephrine bind to receptor won't happen.

09:25 So we know their heart rate will be slower, right, because the SA node increase is blocked.

09:30 The velocity will not be as intense, so that's another reason why it won't move through.

09:35 Now, again, if we think about norepinephrine and epinephrine getting to the beta 1 receptors on the heart, the atrial and the ventricular muscle will increase in velocity and conductivity. What does that mean? Atrium, ventricle, atrium, ventricle, atrium, ventricle are going to be like, atrium, ventricle, atrium, ventricle, atrium, ventricle.

09:52 They're really going to be a lot more intense, unless the patient's taking a beta blocker.

09:59 So, then, the increase in velocity and conductivity is blocked. It's not going as fast and as hard. So you can see, based on what you already know about blood pressure, if the heart rate is slower and it's not pumping as hard, my cardiac output is going to be diminished.

10:17 Therefore, my blood pressure will be lower.

10:21 Okay, so that's pretty cool, right? That's really what we want.

10:25 If we're treating somebody with hypertension, we really want to go after the beta 1 receptors.

10:30 We would call that medication a selective beta-adrenergic blocker, or a selective blocker.

10:37 It will just impact the beta 1 receptors.

10:40 That's usually what we want.

10:42 But stop and pause for a minute and think, "What other beta receptors have we talked about and where are they located?" We have beta 1s on your heart, so where are the other receptors located? You got it. Beta 2s are located on your lungs. Good job.

11:07 Now, before we leave this chart, make sure it makes sense to you.

11:10 You've got the receptor on 1 side.

11:12 What happens in a normal response when the sympathetic nervous system is stimulated? So make sure you've got a note written to yourself up there about norepinephrine and epinephrine response.

11:22 That's the sympathetic nervous system response.

11:25 Over the beta blockers, that's what happens when we give them a med.

11:30 Now, let's take a look at our friends, the beta 2 receptors.

11:32 Yep, you just answered that question about that.

11:35 So we're going to look at what happens when epinephrine hits the beta 2 receptors, and what happens if you have a beta blocker already on the beta 2s.

11:45 Now, we talked about selectivity.

11:47 Really, what we're looking for is more of the selective beta blockers that would just hit the beta 1 receptors.

11:53 But in all honesty, no matter what drug you're on, if it's a specific cardio selective, or beta 1 selective beta blocker, or if you're on one that's non-selective, it hits both beta 1 and beta 2, you could still experience these beta 2 effects, so keep that in mind when we're talking about patient education.

12:12 So let's look at what epinephrine does.

12:14 When it hits the beta 2 receptors, remember, it dilates those arterioles of the heart, lung, and skeletal muscle.

12:20 It's in this diagram too because we're talking about the lung.

12:24 Now, if you've given the patient a beta blocker, it's going to block that dilation.

12:29 Okay, here's where this becomes an issue for your patients.

12:33 Any patient, any patient that we send home on a beta blocker, we need to make sure that they understand if they have any breathing problems, they need to contact their health care provider, okay? So, for you, beta blockers and breathing problems are bad news.

12:51 Beta blockers and breathing problems are bad news.

12:55 So, if you're on a non-selective, you're more likely to have a problem, but people who are on a selective one should just go after cardiac beta 1 receptors on the heart still might have this problem.

13:09 Sometimes, they're going to need their lungs to bronchodilate, and that action will be blocked if they're taking a beta blocker.

13:17 So that's why it's really important that you teach your patients, "If you have any breathing problems, please contact your healthcare provider." Then they can problem-solve with them and assign a different type of medication.

13:28 Because when it blocks that dilation of the bronchi, your patient might feel really short of breath.

13:35 And you don't want that, nor do any of your patients.

13:38 So, you make the difference.

13:40 Educate your patients that, "Hey, you may or may not have this experience.

13:45 But if you notice shortness of breath, you definitely want to do something about that.

13:50 Contact the healthcare provider. Probably not take your next beta blocker based on what the healthcare provider advises you to do." Now, the relaxation of the uterus, this is just kind of a talking point in here.

14:02 Not going to be a major factor when you're taking beta blockers for hypertension.

14:08 We do use beta blockers for sometimes to maybe slow down the process of labor, but that's not the application we're talking about here.

14:16 Now, glycogenolysis in the liver -- remember, that breaks down the stored glycogen when a beta 2 receptor is hit by epinephrine.

14:25 But beta blockers will block this effect. They will block this genolysis.

14:31 This can be particularly problematic for diabetic patients.

14:34 See, a symptom of low blood sugar, which is the biggest risk for our patients that are taking insulin.

14:40 If someone has low blood sugar, what happens is the body kicks into the sympathetic nervous system response.

14:46 It tells the liver, "Hey --" When this epinephrine goes around and is circulating, it tells the liver to kick out stored glycogen to try and raise that blood sugar.

14:56 Here's the problem.

14:57 If the patient's taking a beta blocker, there's 2 things it won't do: normal signs of low blood sugar, our fast heart rate, and their body's going to try and break out that stored glycogen into glucose for blood sugar.

15:13 But if they have a beta blocker, you're not going to have that reaction.

15:16 So the patient's not going to be able to respond to a low blood sugar as quickly and as easily as they normally would because they're on a beta blocker.

15:24 And the other issue is, you're not going to see the tachycardia. Why? Because if the patient's taking a beta blocker -- remember, you don't get that faster heart rate.

15:34 So patients that are diabetic and taking a beta blocker won't show you the typical signs of low blood sugar.

15:42 So it's very important that you educate your patient and their family members to know that, "Hey, if they start to kind of show you some confusion, really check that blood sugar, because you're not going to see the normal signs of fast heart rate, and their body is not going to be able to respond as efficiently by breaking out stored glycogen." Now, the last one, enhanced skeletal muscle contraction, which everybody wants.

16:05 You're not going to have that on a beta blocker.

16:08 So, why does understanding all how receptors work and their response help you? Because once you understand how any receptor responds when it's activated, if we're giving any type of histamine, it's going to be the opposite of that response.

16:23 There's going to be less of that response.

16:25 See, this applies to anti-histamines, right? Instead of allowing histamine to connect to its receptor, then that's how anti-histamines work.

16:34 Beta blockers are the same thing.

16:37 Antagonist, blocker, antis, that's what all these drugs do, is they block the response of that receptor.

16:45 Now since you know what beta 1s and beta 2s do, you can easily remember how the patient will respond.

16:52 So the non-selective ones block both beta 1s and beta 2s.

16:56 That's why they're called non-selective.

16:59 Labetalol, propranolol, those are 2 really good examples.

17:03 Now, the ones that are selective, these guys are a little newer and a little more expensive: atenolol, bisoprolol, esmolol.

17:10 Okay. But also keep in mind that even if it's supposed to be selective, with certain patients and different times, they may also have beta 2 stimulated also, the goal is primarily beta 1, but it's not exclusively beta 1, depending on how the patient is doing.

17:28 So let's pause for just a minute and focus on a question.

17:32 Let's see if you can remember some easy things.

17:34 Where are beta 1 receptors located? Good. On the heart.

17:40 Where are beta 2 receptors located? Good. On the lung.

17:47 Why do I want a patient with asthma to be on a selective beta blocker? Remember the benefit for being on a selective beta blocker is we're going to minimize the risk of that asthma patient needing to bronchodilate and having that response blocked.

18:10 So we probably would look for another medication for an asthmatic patient, but any patient that we put on a beta blocker, we always teach them, "Beta blockers and breathing problems are bad news."