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Intravenous (IV) Fluids, Intravenous (IV) Solutions and Tonicity (Nursing)

by Rhonda Lawes

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    00:00 Hi. Welcome to our video on IV fluids. This is going to be so fun. I want you to be aware of the risks and the benefits every time you hang an IV fluid. Just hang out with us for a little while longer and we'll explain all of those. Now, we couldn't really teach you about IV fluids until we start thinking about where fluid is in your body. So, where is all that fluid? Well, 40% of the total fluid is intracellular. It's inside your cells. The other 60% is outside of the cells. So, as we're getting started I just want you to keep in mind where is the fluid in your body, outside the cell or inside the cell? Those are your first 2 options. So, inside the cell we just call intracellular. That's not very exciting. Right? But outside of the cell, we've got 2 other places fluid could be. Interstitial or it can be intravascular. Okay, so let's not get ahead of ourselves.

    01:03 Start with the green boxes. If you're asking where fluid is, first is either inside the cell or outside the cell. Everybody with us? Okay cool. Inside the cell, we call that intracellular. Outside of the cell, we call that interstitial or intravascular. Interstitials can like all around my tissues in my cells. Intravascular is in my vessels. Remember I'm supposed to say an intact system, from my right atrium when it goes all the way to back up and back to my right atrium. That should be a close system. That's considered your intravascular space. Inside the cell, outside the cell. Why do we keep going over that? Trust me it's going to matter when we hang IV fluids because it's going to cause fluid to shift back and forth between those spaces. So, interstitial is between the cells and in the tissues. Intravascular is inside the blood vessels. Okay, I'm going to feel better if we do this just one more time. Fluid is either inside the cell or outside the cell. The 2 places fluid is when you're outside of the cell, interstitial or intravascular. Now before we go on, see if you can sketch that out really quickly in your notes. Trust me, it's going to matter as we get going. Now let's look at the specific IV solutions. You'll be hanging. Isotonic means equal. Iso means equal. You're not going to have any fluid volume shifting differences. So as much goes in or out everything will be, like I said, equal. The next type of solution is hypotonic.

    02:44 Now that means that it's a solution that's less tonicity than what your serum's blood is. So it will cause fluid to shift into the cells. So then the cells get bloated. So when I hang a hypotonic solution, it will cause fluid to shift into the cells. So we talked about isotonic, hypotonic, now we're talking about hypertonic. Hypertonic solutions, look at those cells. Compare them in the first example for isotonic, they look about the same. In hypotonic, starting to swell. You see those arrows going into the cell. For hypertonic, look at them, they look like dehydrated potato bugs.

    03:27 They all shrivels up. Because if I hang a hypertonic solution, it's going to cause fluid to shift out of the cells and that's why they look so dehydrated. Now, this would be no fun if we just ask you to memorize this. So we're going to explain to you why isotonic, hypotonic and hypertonic solutions have the impact on the cells that they do. But before we do, I want you to understand the risks. Hypotonic solution goes into the cell, causes that cell to swell. The place I'm most worried about that is in your head, the cells in your head, because when those cells swell inside my skull, in my brain, it can cause an elevated intracranial pressure. That's what ICP means. So if you make those cells swell enough, I'm really going to have some risks for damaging my brain.

    04:25 Now when fluid leaves the intravascular space and rushes in to the cells, my blood pressure is going to drop or lower. Depending on how severe I am or how much fluid you hang, I might be at risk for cardiovascular, boom, collapse. Pressure just bottoming out and going into shock. This also causes third-spacing because we're shoving things also into the interstitial space. So third-spacing means I've got fluid in inappropriate places. That's what third-spacing is. I should have the equal amount on my intravascular space and my tissues will be kind of moist but third-spacing is like, think of it as edema, it's inappropriate fluid placement. Now, hypertonic is going to lead us to dehydrated cells and we're also may be at risk with patients with DKA because people who are in diabetic ketoacidosis are already extremely dehydrated. So, you want to keep in mind this is a great summary slide. I know you don't quite understand it all yet or if you do "Wow, I'm impressed with you" but I want to explain the rationale to you on why these things happen. Isotonic - relatively minimal change. Hypotonic - I'm going to have fluid rush into the cell. Big problem for people of elevated intracranial pressure might drop their blood pressure and they're going to have edema or third-spacing. Hypertonic - woo I'm going to dehydrate that cell. So it's a problem with people who have extreme dehydration like DKA. So what are we talking about; in the cell, out of the cell, rush in, rush out. But I want to introduce you to a term you've probably heard back in junior high lab classes. But osmolality is the number of osmoles per kg of water.

    06:14 Yeah, okay. Did I lose you there? I mean have you fallen asleep yet, but hang with me this is good. We usually use it to describe fluids inside the body or the cellular concentration in fluid by weight. Yeah, I know, not extremely exciting. Is it? Osmolarity is the number of osmoles per solution of liter. Uhmmm, yeah, I know. This new is fast, but remember 1 liter of water equals 1 kg in weight in case you did know it. So, we're going to kind of use these terms as equivalence.

    06:45 So don't let it confuse you if it says osmolality or osmolarity, whatever you got there. They're kind of equal terms for our uses. Their normal levels are the same and so we're just going to use these interchangeably. So if you're real chemistry nerd, I get it why you might be offended by that but for our uses we're going to run with it. So, what is tonicity? Well, when you say hypertonic, isotonic. Or what was the other one? Hypotonic. Good. We're going to talk about what is tonicity. It's the concentration of dissolved molecules that are within a solution. Now here's where this is going to start to get much more interesting for you. Osmolality of plasma. What's in my intravascular space is usually about 270-300. Okay, so that's an important number. Kind of circle that one for yourself. So, I would imagine that if a solution is isotonic, would it be equal, higher or lower osmolality? Look at that how they've got the colors across the top to let you see the 270-300 that's normal. Isotonic solutions right there. It's a great slide summarized for you. You can see that isotonic solutions are pretty close to equal of what your serum is, what your plasma is. We've got them all listed for you there. Now if it's higher greater than 300, that makes it hypertonic. If it's lower, that makes it hypotonic. Okay? So again, another greater summary slide for you. That's when I would ____ and put in my pocket if you had it. So tonicity is the tonicity of the fluids, isotonic fluids, and we just saw on that beautiful slide close to 300, same as my plasma. Hypertonic, greater than 300 osmolality. And hypotonic is less than 300. Now just for fun, which way this fluid shift with an isotonic fluid? Trick question, right? It shouldn't really shift because it matches the same tonicity. Now we're going to remember what happens if you hang a hypotonic fluid. When I hang a hypotonic fluid into my serum, right, into my vein now all of a sudden I am more intense or saltier because salts are predominant electrolyte. Since I've hang a hypotonic solution, I'm saltier inside my cell that's why fluid rushes into the cell.

    09:24 With hypertonic fluids, now I'm saltier or more concentrated outside of the cell in my intravascular space and fluid is going to rush from the cell into my intravascular space. Okay, we'll keep going over that. Don't worry if it sounds a little confusing, sometimes it is when you first start looking at this but I promise you it's going to click.


    About the Lecture

    The lecture Intravenous (IV) Fluids, Intravenous (IV) Solutions and Tonicity (Nursing) by Rhonda Lawes is from the course Medications for Fluid and Electrolyte Imbalances (Nursing). It contains the following chapters:

    • Where is all the Fluid?
    • IV Solutions
    • OsmolaLity - OsmolaRity
    • Tonicity

    Included Quiz Questions

    1. 60% intracellular/40% extracellular
    2. 50% extracellular/50% intracellular
    3. 60% extracellular/40% intracellular
    4. 70% extracellular/30% intracellular
    1. Isotonic, hypertonic, hypotonic
    2. Protonic, hypertonic, isotonic
    3. Hypertonic, hypertonic, protonic
    4. Isotonic, protonic, hypotonic
    1. Edema from third-spacing
    2. Dehydration
    3. Hypotension
    4. Increased intracranial pressure (ICP)
    5. Hypertension
    1. 270–300 mOsm/L
    2. 310–560 mOsm/L
    3. 103–270 mOsm/L
    4. 300–406 mOsm/L
    1. Tonicity
    2. Edema
    3. Osmolality
    4. Osmolarity

    Author of lecture Intravenous (IV) Fluids, Intravenous (IV) Solutions and Tonicity (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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