Do you get really confused by all the different types of IV fluids? Hypertonic, hypotonic, isotonic, cells shrinking, cells swelling, who knows what's going on, right? Well, I've got a solution for you.
See what I did there? My name is Nicole Weaver. I'm an educator with NRSNG. I've been a nurse for 10 years.
And I've worked mostly in critical care and emergency medicine, which means I have given a ton of these IV fluids. Now, I remember learning about this in nursing school and being so confused. And even after I was working as a nurse, it was really a struggle to understand why we gave the different types of solutions. So my goal here for you today is to really demystify this, take all the guesswork out of it and help you really know what solution you need for your patient. So the first thing you've got to know to understand what's going on with IV solutions is that it's all about osmosis.
Osmosis is the process of water moving across a semi-permeable membrane along a concentration gradient. Now don't get confused here. Anytime you're talking about diffusion or osmosis, you're talking about that substance moving from where that substance is high to where that substance is low, specifically.
So with osmosis, if you have more water on one side and less water on the other, it's going to move from where there's more water to less water. So let's say we have a semi-permeable membrane, and on one side we have a very dilute solution, meaning there's only a few particles, lots of water. On the other side, we have a very concentrated solution, lots of particles.
Not much water. What's going to happen by osmosis is the fluid or the water is going to move from the area where it's dilute to concentrated because there's more water and less water. So you're going to have to understand that we're specifically talking about the movement of water or fluids.
So now remember, we have three categories of IV fluid solutions, hypertonic, isotonic and hypotonic. Hyper means more, iso means the same and hypo means less. less.
So more than what? Less than what? What are we even talking about?
What we're comparing it to is the blood plasma. And tonic or tonicity refers to stuff, the amount of stuff that's dissolved in it. So hypertonic is a solution that has more stuff dissolved in it or is more concentrated than the blood plasma. Hypotonic means it has less stuff or it's more dilute than the blood plasma. And then isotonic means it's about the same.
So think about this. As our blood plasma sits in our body, it's not moving anywhere, right? We don't have any fluid shifts happening. We're not swelling up our cells. We're not shrinking our cells.
Everything's just balanced. That's homeostasis. Our body always wants to be in that balance.
So if I add a solution into my bloodstream that's more diluted, more concentrated, it's going to throw off that balance, and it's going to cause fluid to have to shift in order to restore that homeostasis. So I've got to understand what's going to happen, what fluid's going to shift where, and what's that going to do to my patient. So when we talk about isotonic solutions, we're talking about a fluid that basically matches the concentration of our blood plasma. So if it matches, is anything going to have to move anywhere? Nope.
So the big goal of giving isotonic solutions is actually to put fluid into the bloodstream and have it stay there. Sometimes you'll hear it called a volume expander, but it just depends on what you're doing. So we want to put it into the bloodstream and have it stay there.
The two most common examples of an isotonic solution are NS or normal saline or 0.9% sodium chloride or LR or lactated ringers. Now, the big question I always get asked is what's the difference and how do I know which one I need to be giving? LR has something that NS does not. LR has electrolytes in it, things like potassium, magnesium, lactate. And so what we want to do is think about does this patient need those extra electrolytes?
So the most common time we have LR over NS is when we have a patient who has lost whole blood. That means maybe they had a trauma. Maybe they had a surgery.
Maybe they have a GI bleed and they're actually bleeding somewhere, but they have lost whole blood. We're usually going to give LR because we can kind of replace some of the electrolytes they lost as well. Now, if you have a patient who's just lost fluid, they're just super dehydrated.
Maybe they've been vomiting and they've lost fluid that way. We're actually just going to give them normal saline. We just need to replace their fluids. We don't necessarily need to worry about all of their electrolytes as well. So as a general rule, remember nothing's black and white.
No one reads the textbook. But as a general rule, we're going to see LR used in surgical trauma patients. And we're going to see NS used in medical patients.
Again, nothing's ever black and white, but that's a general idea. So let's talk about hypotonic solutions. Hypotonic means it has less stuff dissolved in it. which means it is more dilute than the blood plasma.
So if I put a hypotonic solution into my bloodstream, I'm going to have more water outside of my cells in my bloodstream than I normally would, right? So if I have more water on the outside, where's the water going to go? Well, the water is going to have to shift into the cells and the cells are going to swell. That's the only way we can maintain that balance. Now, I know what you're thinking.
Why the heck would I give an IV solution that's going to cause my cells to swell? That makes no sense, right? Well, you're right.
We would never want to intentionally make our cells swell. They swell too much. They can burst.
But think about this. What if I had a patient with cellular dehydration? I have a patient whose cells are already shrunken, right?
So... wouldn't it be beneficial to give them a hypotonic solution, force some of that fluid back into the cells to restore the normal hydration of their cells? So classic examples of this would be things like DKA, diabetic ketoacidosis, or HHNS, hyperglycemic hyperosmolar non-ketotic syndrome, because they experience profound cellular dehydration. Now, a lot of times when we start treating these patients, we'll just give them isotonic just to build up their fluid volume.
But we're almost always going to end up giving them a half normal saline or a D5 half normal saline once their sugars are managed, because it really helps to restore the hydration of their cells and fix some of those symptoms that they're experiencing. For other patients, you may also see things like D5W or D5 in water. Either way, all of these things are going to have a lower percentage than normal saline. Normal saline is 0.9%, half normal is 0.45.
So pay attention to those percentages as well. So let's look at hypertonic solutions. You're going to see basically the opposite action, right?
So if I have a hypertonic solution, it has more stuff dissolved in it, which means it is more concentrated than our blood plasma. So when I put that solution into my bloodstream, I now have less water outside of my cells proportionally than I had before. So where's the water going to go? Well, it's going to come out of the cells.
The cells are going to shrink. Again, you're thinking, why would I intentionally shrink? my cells?
You wouldn't. However, what if we had a cell that is already swollen? For example, cerebral edema. So in cerebral edema, one of the biggest treatments we do is hypertonic saline or 3% saline.
We're going to put that hypertonic saline into the bloodstream. The fluid's going to come out of those swollen cells and into the bloodstream. The cells are going to go back to normal.
Patient's going to pee out the extra fluid and we will have really, really helped the problem. Now I worked in a neuro ICU for a while and I can tell you this works wonders on these patients. So again, our goal is not to intentionally shrink the cells.
Our goal is not to intentionally swell the cells. What we're trying to do is restore that balance, restore that homeostasis. Of course, we can always overshoot it.
So be paying close attention to how your patient's doing, how much you're giving, how fast you're giving it, because you could always overcompensate and overswell or over shrink. but it's really important that you at least know what's happening inside your patient, because then you can be an incredible patient advocate. Let's say you have a patient with cerebral edema, and your provider comes in and orders half normal saline.
And you're thinking, that's hypotonic. I know that hypotonic makes my cells swell. He's already swelling. I really feel like this is a bad idea.
And you can actually go to your provider and have a conversation about that. So there's a couple memory aids for you. You can remember hypo equals hippo, like a big hippopotamus.
And so you can remember they're big fat swollen cells. And hyper, you can think hyperactive and exercising a lot and getting really skinny. So those are just memory aids, but it's really important that you understand that it's all about osmosis, know what's happening to your patient and why you're giving that fluid. So I hope that really helps to demystify IV fluid solutions.
Really, if you understand osmosis and you know normal, it's easy to figure out what's going on to your patient. Make sure that you check out the IV fluid solutions cheat sheet. that talks about all the different common solutions that we give, what their osmolarity is, what their tonicity is, what we give it for.
All of that are so much great information on one page. It's incredible. You can also jump over to NRSNG.com because we've got lots of lessons on fluid solutions, fluid shifts, fluid types, all in a lot more detail than I can present here. Remember, you don't have to struggle through nursing school alone. Jump over to NRSNG.com, start your trial, and let us help you through it.
Happy nursing.