Fluid Volume Status – Determinants of Blood Pressure (Nursing)

00:01 Moving on to our last part of our four parts of blood pressure is our fluid volume status.

00:06 Now, we talked about it being measured by CVP and PAD.

00:10 Remember, those are trending values not absolutes, our CVP normals, 2-8 mm Hg, our PAD normal is 6-12 mm Hg.

00:18 But every heart may need a different number for it to be optimized with fluid.

00:24 Remember, we talked about stroke volume variance and delta stroke volume, those two numbers are a better indication of fluid volume status.

00:34 Fluid volume status is again, the preload going into the heart.

00:37 So your CVP is the pressure going back into your right ventricle.

00:42 And your PAD, your pulmonary artery diastolic pressure is the pressure going back into the left ventricle.

00:49 We have to have enough pressure so that we get enough blood volume in our right ventricle and left ventricle and enough stretch so that we can get enough contractility.

01:00 So more fluid should equal a higher CVP or PAD.

01:06 But how does fluid volume status affect cardiac output? Well think about it.

01:11 If we don't have enough blood volume going into the right and left ventricle, we're not going to have enough volume coming out of the ventricles.

01:18 So not enough fluid volume status going into the right ventricle or left ventricle or not enough PAD or CVP equals not enough cardiac output.

01:27 Let's think about this in a long, broad stroke way.

01:33 So if we increase our CVP, our central venous pressure, we're increasing our venous return into the right side, which means we're increasing our end-diastolic pressure.

01:44 That increases muscles stretch, which then increases our stroke volume, which then increases cardiac output and increases our MAP.

01:54 All that to say more volume should increase our cardiac output and our MAP up to a certain point, we want to be what's called fluid optimized.

02:05 Now what's a quick way that we can identify if we do not have enough blood volume or fluid volume status, and we need to increase it to increase our MAP? Well, that's when we go to our delta stroke volume.

02:17 Remember, I talked about delta stroke volume is giving embolus and seeing if we have a 10 to 15% change.

02:23 Well, you can talk to the physician and say, "Hey, can I get embolus of 250 or 500?" And we'll squeeze that in fast and we'll see if we have a percentage change.

02:32 They call this sometimes a fluid challenge.

02:34 But sometimes they'll say, "No, I don't want to give too much fluid." Well, what we can do is called the passive leg raise maneuver.

02:41 Basically, the patient needs to leg flat and then elevate their legs to 45°.

02:49 When they elevate their legs to 45°, this causes an auto transfusion of blood about 300 to 500 mLs of blood, Keep their legs up for 2-3 min and what you're watching for is you want to see a cardiac output or stroke volume change of at least 10-15%.

03:06 If you don't see a 10-15% change, then they do not need more fluid volume.

03:12 If you have greater than a 10-15% change, then they do need more fluid resuscitation.

03:18 So how does central venous pressure relate to venodilation? Venodilation and CVP are inversely proportional to one another meaning if I vasodilate my venous side, I will drop my CVP.

03:32 If I vasoconstrict my venous side, I will increase my CVP.

03:37 Just have in mind if you're adding medications that are going to vasodilate the whole vasculature system, so it's gonna vasodilate the arterial side.

03:45 It may also vasodilate the venous side and drop the return back to the heart meaning decrease the CVP.

03:53 Let's look at this in a more simplified way.

03:56 I don't know if you've been around some nurses that say, "Hey, the patient's tank isn't full or the patient's tank is full", when they talk about fluid status.

04:04 When I visualize that I think of a fishbowl demonstration or a tank demonstration.

04:10 So if you think of the fishbowl, think of that as the patient's tank, the vasculature.

04:16 And the amount of fluid is there CVP.

04:19 So, when the fishbowl is at normal size, their tank is full, so the CVP you know, let's say it's around 16.

04:27 But let's vasodilate that venous side.

04:31 We make that tank bigger and we don't add any fluid.

04:35 So they're CVP is going to decrease, their tank isn't as full.

04:39 So when we're vasodilating the venous side, we may need to administer some fluid to accommodate that vasodilation that just occurred.