Hematocrit (Hct) and Hydration Status (Nursing)

by Rhonda Lawes

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    00:01 So that was the hemoglobin. Now let's look at the hematocrit.

    00:05 Remember, the hematocrit is a percentage of the overall solution.

    00:09 So we're looking at the packed cell volume.

    00:12 Look at that first test tube. You've got a purple top because that's the one that we put blood in for a CBC.

    00:18 You draw the blood, fill the tube, and we used to have to put it in a centrifuge. Historically, it was this machine that would whip these tubes all the way around.

    00:28 It would help it separate to show us the 55%, 1%, and 45%.

    00:33 Now we can just calculate that.

    00:35 So we're looking at hematocrit as the packed cell volume, PCV.

    00:40 It's measured as a volume percentage.

    00:42 Remember, hematocrit is the volume of the red blood cells, the percentage of that volume, and we get that from the CBC test.

    00:50 But here's something that starts to get really cool.

    00:52 Now that you've done the work of laying all that groundwork of understanding what red blood cells are, what they do, looking at what hemoglobin and hematocrit is, now let's talk about hematocrit and hydration status. Because remember, the percentage of red blood cells is compared to the total volume of the blood.

    01:11 Now, can you recall, do we have a higher percentage of plasma or red blood cells? Well, look at your picture for a clue. Right.

    01:19 Normally, you have a higher percentage of plasma.

    01:22 Now, when red blood cells and hemoglobin are normal -- like your patient isn't going through any chronic issues, the red blood cells and hemoglobin are normal -- it's usually a matter of 3 times the hemoglobin will give you the hematocrit.

    01:36 So, remember, you have to have a normal red blood cell and a normal hemoglobin.

    01:41 3 times a hemoglobin will equal your hematocrit.

    01:44 So that's just a quick number game that you can play the next time you look at a patient's values that are within normal status.

    01:50 Now here's what happens with hematocrit when you have a + or - in the plasma volume.

    01:56 Here's what the impact that you're going to see.

    01:58 If the patient has lost fluid or lost plasma volume from the vascular space, it will raise their percentage of red blood cells.

    02:06 Now, you don't have to do tricky math to do that, but if you look at that test tube and if the amount of plasma or fluid volume decreases in the blood, that way, the blood is going to now take up a higher percentage because there's less plasma.

    02:20 Now, reasons you would have that would be like intravascular dehydration.

    02:24 That means that the amount of volume is in my intravascular space -- my veins and my arteries -- is less fluid.

    02:31 Not less red blood cells, but less fluid.

    02:34 So how that can happen? I can have intravascular dehydration, I might have a severe burn.

    02:40 In severe burns, those capillaries are damaged. Remember, the capillaries are what help us keep fluids in because we have that oncotic pressure from protein.

    02:49 But if I'm severely burned, those capillaries are damaged and fluid is going to leak out of my intravascular space into my tissues.

    02:58 So I'm going to have an elevated hematocrit, not technically because I have more red blood cells -- remember, it's a overall percentage.

    03:07 So if I have this reason for having less fluid volume in my intravascular space, then my percentage of blood is now going to be higher, because the ratio is different.

    03:16 I have less fluid volume, so it looks like I have a higher percentage of blood.

    03:22 Now, what do you think happens if you become over hydrated, if you have too much fluid in your intravascular space? Do you predict that the hematocrit would go up or down? Remember, hematocrit is the total percentage, right, of the red blood cells compared to the whole volume.

    03:39 If you have overhydration, we're going to have extra fluid in the intravascular space.

    03:44 So what's your guess? Right. You're going to have a decrease in hematocrit.

    03:50 So this plays a role when you're looking at your patients, right? If they're dehydrated, their hematocrit is going to look like it's really low.

    03:57 So when you rehydrate them -- boom -- it's going to drop, and you're going to think like, "Oh my goodness. Are they bleeding out?" No. When you recognize that a patient is dehydrated, and that was the rationale for the hematocrit being low, you give them IV fluids to replace that volume, you would expect the hematocrit to drop.

    04:18 Just to go over that one more time.

    04:20 The percentage of red blood cells as compared to the total volume of blood -- So, if I have more or less in the plasma volume, it will impact your hematocrit.

    04:28 It doesn't mean your patient is bleeding. It just means that a + or - in the plasma volume will impact your hematocrit.

    04:36 Now let's get real fancy. Let's look at a trauma patient.

    04:39 So when they have equal loss of red blood cells and plasma, that means they've had a significant hemorrhage, right? So, it's not a matter of dehydration where they lost more fluid volume and didn't lose red blood cells.

    04:51 We're talking about, you've cut a major artery and blood is just leaking, or you have a big internal bleed.

    04:58 So immediately after that hemorrhage, there's no significant change in the hematocrit because you've lost equal parts of the fluid and the red blood cells.

    05:05 But hours later, your body's going to rush where you're like, "Oh, my goodness. We do not have enough volume in the intravascular space." So what it does is it will shift interstitial fluid into the vascular space to try to compensate for that fluid loss.

    05:19 Okay, now what's going to happen? What's going to happen to that hematocrit if we shift extra fluid into the intravascular space because the body registers that you've hemorrhaged and bled out equal parts, plasma and red blood cells.

    05:33 Now it's shifting interstitial fluid space in, what's going to happen to the hematocrit? Yeah, that's why you're going to see a decrease in the hematocrit.

    05:42 The bone marrow takes 10 days to mature a red blood cells.

    05:46 That's why people who've lost a lot of blood have to receive packed red blood cells or they're not going to make it.

    05:52 So, immediately after hemorrhage, no significant changes in the hematocrit because you've lost equal amounts of blood and plasma.

    06:00 Hours later, when you have that fluid shift to compensate for the fluid loss into the intravascular space, the hematocrit will then show you a decrease.

    06:08 And remember, the body can't respond to this quickly.

    06:11 It's going to take 10 days for extra red blood cells.

    06:14 So whether it's an acute loss, like we just talked about with hemorrhage, or a chronic blood loss, it matters.

    06:20 So, star this note and let's walk through why it does.

    06:25 An acute loss -- the body doesn't have time to respond -- and a chronic loss -- it's a more gentle change and the body has time to adapt.

    06:33 So if I have an acute massive hemorrhage, I'm going to have an increased risk for hypovolemic shock.

    06:38 If I have somehow severed an artery and blood is leaking out everywhere, I'm at a risk to have low volume in my intravascular space, which means I'm at risk to go into shock.

    06:49 Now shock means I don't have enough oxygen getting to my tissues to meet its metabolic needs.

    06:55 I don't have enough volume in my intravascular space.

    06:58 That's the reason why I don't have enough oxygen.

    07:00 People who have chronically low hemoglobin, like dialysis patients who have renal failure, they'll tolerate a much lower hematocrit than you or I would without going into shock.

    07:11 Because the body came to that state gradually, it had time to try and compensate.

    07:16 Remember, renal failure patients are the ones that have to get that erythropoietin, like my dad, because it stimulated his bone marrow to make red blood cells.

    07:25 Now, here's another thing I want you just to file away.

    07:27 Each unit of packed red blood cells should raise the hematocrit approximately by 3%.

    07:33 So by looking at what your patient's somatic rate is, you'll know when you hang a unit of blood, we would expect it to raise about 3%, if they're not still chronically bleeding.

    07:43 Okay, so let's hit the critical values.

    07:45 Hematocrit of <15% can result in cardiac failure.

    07:50 A hematocrit of >60% can result in spontaneous blood clotting.

    07:56 Think of the blood as being too thick and where it's at risk for extra clotting.

    08:00 But there's a special note about pregnancy. They have a decreased hematocrit, especially in the last trimester because that plasma volume increases.

    08:09 Now, see if you can remember why does a plasma volume increase cause a lower hematocrit? Right. Because hematocrit is a percentage, and if you increase the plasma volume, then ratio wise, you're going to have a lower hematocrit.

    08:22 In children, it just really varies with age.

    08:25 I know. That was a lot of help, but just keep that concept in mind.

    08:28 For kids, it will vary with age.

    About the Lecture

    The lecture Hematocrit (Hct) and Hydration Status (Nursing) by Rhonda Lawes is from the course Complete Blood Count (CBC) (Nursing).

    Included Quiz Questions

    1. The percentage of volume of the red blood cells
    2. The percentage of volume of the white blood cells
    3. The percentage of volume of the hemoglobin
    4. The percentage of volume of the plasma
    1. 3:1
    2. 2:4
    3. 1:1
    4. 5:3
    1. Hematocrit levels will rise.
    2. Hematocrit levels will decrease.
    3. Hematocrit levels will stay the same.
    4. Hematocrit levels are not measured in a CBC.
    1. Approx. 3%
    2. Approx. 19%
    3. Approx. 30%
    4. Approx. 9%

    Author of lecture Hematocrit (Hct) and Hydration Status (Nursing)

     Rhonda Lawes

    Rhonda Lawes

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