Hemodynamic Aspects of Blood Pressure (Nursing)

00:01 So we've learned our human dynamic values.

00:04 Now we need to learn the concepts and how to apply these values.

00:10 Let me go over a little bit of definitions and principles for you.

00:13 Hemodynamics, what it means is the measurement of blood flow.

00:17 That's all it is.

00:18 This was first discovered in 1628.

00:21 What's important to know is that the clinicians must know how to interpret the data, and how to apply the data correctly.

00:29 When we're just learning this, there's a key to it.

00:31 And that key is to simplify everything, simplify it into basic terms and understanding and then we can start building on top of it.

00:41 I want you to remember that oxygen delivery is the goal.

00:45 When I first started learning this, I got these algorithms of oxygen delivery is DO2 which equals cardiac output and calcium and what is cardiac output and what caO2.

00:57 And then we learn about what's oxygen consumption, that's your CVO2 and all this and it looks all like a big mumble pile of basically stuff that I don't understand, especially when I'm starting.

01:12 All you need to know is the goal of our heart and our vascular system is to get blood and oxygen to the body.

01:17 That's all this is saying with oxygen delivery and oxygen consumption.

01:22 Just keep in mind, let's simplify it.

01:24 The goal of the heart and the vasculature system is to get blood and oxygen to the body.

01:30 So if the goal of our heart and our vasculature is just to get enough blood to the body, how do we know that's happening? How do we know that the heart is getting up blood to the body? Well, we have a value called the mean arterial pressure.

01:44 This is the average pressure in our clients arteries, we have a systolic and diastolic on our blood pressure.

01:50 But the mean arterial pressure is a better indication of organ perfusion.

01:55 We want that mean arterial pressure between 60 to 65 or greater.

02:00 If it's 65 or greater, then we know that we're getting enough perfusion to all of our organs.

02:05 If it's under 60 or under 65, then we may not have enough blood pressure and enough blood volume getting to all of the organs.

02:14 So how do we look at the blood pressure? And how do we look at the determinants of that? Well, I've divided these into what's called the four parts of blood pressure.

02:26 So looking at a blood pressure, what makes up a blood pressure? What makes up the mean arterial pressure? They're divided into two areas, two parts of the heart and two parts of the vasculature.

02:39 Let's look at the heart.

02:41 So what determines the blood pressure with the heart? You have what's called the heart rate, and you have the contractility of the heart.

02:51 We'll look at those a little bit more in depth.

02:53 Then over to the vasculature, what two parts of the vasculature or the body make up a patient's blood pressure? That's vascular resistance and fluid volume status.

03:03 Let's look at these a little bit closer.

03:05 Well, with heart rate we look at, we can look at our ECG monitor to get how fast our heart rate is, we can also take a pulse.

03:13 But what's important to know is that with heart rate, we also need to know the heart rate rhythm so that it's normal, because you can affect your blood pressure if you're in a different rhythm, like atrial fibrillation or sinus tach.

03:26 So it's not just the heart rate, but also the heart rate rhythm.

03:29 So we really want to look at our ECG monitor to see what our rhythm is.

03:34 Now, how do we look at contractility? Well, the best way to look at our contractility is often echocardiogram, so you can actually see the heart and see how it's squeezing.

03:46 But we don't always get an echocardiogram.

03:48 So you could secondarily look at your contractility with cardiac output.

03:52 We're going to dive into that a little bit deeper so that we have an understanding because you can't look at your cardiac output, and it's low and go, "Okay, my contractility is not strong enough." because there's so many determinants into it.

04:05 But we'll get into that a little bit later.

04:09 Just know that the best way to look at your contractility of your left ventricle is your echocardiogram.

04:15 Now, how do we look at vascular resistance? How do we look how tight or how dilated our vasculature is? Well, we have our systemic vascular resistance that lets us know if we're vasoconstricted or if we are vasodilated.

04:31 And then fluid volume status.

04:33 How do we know if we're hypervolemic, normal volimic, hypovolemic, if we need fluid, if we need to take some fluid out, how do we know that? Well, remember, we have our CVP and our PAD, our central venous pressure and our pulmonary artery diastolic pressure.

04:49 Those are the pressures going into the right ventricle and into the left ventricle that can indicate fluid volume status.

04:56 But we're going to use those as trending numbers not as absolute numbers.

05:00 We can also use what's called your stroke volume variance, or your delta stroke volume.

05:06 Let me talk about these a little bit more in depth.

05:08 Stroke volume variance is just the change in the stroke volume from beat to beat.

05:14 So let's say we have a stroke volume of 80 mLs, and then the next beat 72 mLs and the next beat 85 mLs.

05:21 So it's going to measure the percentage of change, we want it up under about 13%.

05:28 If it's above 13%, that's an indication that we do not have enough fluid.

05:34 But there's some barriers to this, we have to make sure that we are in a normal rhythm.

05:39 We cannot have any AV disassociation.

05:43 What that means is that the atrial contracts and then the ventricle contracts.

05:47 So we cannot be in AFib, we cannot be in aflutter, or we can't be in a heart block.

05:52 That will cause AV dissociation.

05:54 And that'll give us an inaccurate stroke by variance.

05:57 We also have to be intubated so that we have the same amount of pressure in there.

06:03 If we breathe big one time, and then we breathe smaller the next time, that difference in pressure will change our stroke volume variance.

06:14 Delta stroke volume is probably the best way to identify our fluid volume status.

06:19 What that means, what delta means is a change.

06:23 So what we're looking at is what's the change in stroke volume after a bolus.

06:27 So we look at our stroke volume, you can also use cardiac index.

06:33 And what you want to see is if you give a bolus and I'm talking real fast, it only has to be a bolus of 250 to 500.

06:39 But we really need to bolus it in not just put it to gravity really quickly, or not just put it on the pump to 999 mLs an hour, but actually put a pressure bag in and get it in there pretty quickly.

06:51 So once that said we're gonna look at our stroke volume, and if it increases by 10 to 15%, that lets us know that we are still hypovolemic and we need to add more fluid.

07:03 So then we can keep giving boluses of 250, 500, maybe even 1000 depending on what's going on with the patient to get to our optimal stroke volume.

07:13 So, with delta stroke volume, we're going to give a bolus, we're going to give it as quickly as we can, and we're gonna see the percentage of change in the stroke volume.

07:22 So if it's greater than 10 to 15%, then that lets you know you need to keep giving a little bit more fluid until we get under a change of 10 to 15%.

07:32 Then we are called what's fluid optimized, meaning we don't need any more fluid.