(Here’s where you can read an UPDATED VERSION of this article about Hypertonic Solution)
If you’re looking for a list of IV solutions to memorize, then you’re in the wrong place.
But if you want to understand WHY and HOW IV solutions work the way that they do so that you can become a better nurse…here you go!
If you haven’t already seen the results of my osmosis experiment from last week, make sure to check that out, because I’ll be referring to it in all of my posts this week.
When talking about IV solutions, most people would be tempted to jump right into Isotonic, because those are the most commonly used. But I just can’t wait to talk about Hypertonic IV fluids because after doing my osmosis experiment last week, I think they’re really stinkin’ cool.
And yes, I do realize that makes me a really big nerd 🙂
Let me back up a second. Do you understand what Hypertonic solutions are? It’s a fluid that contains a higher amount of solute than whatever we’re comparing it to. How’s that for a vague sounding definition? Seriously though, in nursing, we’re always comparing solutions to the human body! So when we say that an IV solution is Hypertonic, what we are really saying is that it has a higher solute to solvent ratio than blood does. Blood basically becomes our definition of what “Isotonic” means, but that article will come later this week.
Why do I think hypertonic fluids are so cool? Just take another look at the “after” pic from my osmosis experiment up above! The permeable membranes (aka eggs) that were in the Isotonic and Hypotonic solutions only had a very minor size difference…but the egg placed in the hypertonic solution shows a drastic change! The water has been sucked out into the hypertonic solution via osmosis, causing a very serious case of egg-dehydration.
Applying this concept to nursing can be a little bit confusing at first. After all, it’s hard to visualize how a patient could become “dehydrated” as a result of us putting IV fluid in them! Let me break it down a little bit for you.
With this egg experiment, we were only really working with one semi-permeable membrane: the egg membrane. The human body is much more complex, and has many different parts that interact and influence each other. The body also has more than one semi-permeable membrane to help regulate where fluid in the body is supposed to be.
One of many semi-permeable membranes happens to be located around Red Blood Cells (RBC). So if you’re not careful RBCs that begin to get “dehydrated” like that are going to die unless the water balance is reversed. Obviously, that’s not a good situation for our patient to be in! So even though our patient appears to be well-hydrated, and perhaps has been urinating appropriately, they’re RBCs are dehydrated simply because of the type of solution we injected into their body.
Another semi-permeable membrane you need to consider as a nurse is the blood vessel walls. When you inject hypertonic solution into the blood vessels, not only do you risk draining RBCs, but that hypertonic solution is also going to attract water from outside of the blood vessels! All of this additional water moving by osmosis into the blood vessels can quickly cause high blood pressure (and all the complications that come with it) if not done carefully.
So what type of IV solutions are hypertonic? These are the common ones:
Notice that three of the solutions contain Dextrose, which is a sugar. The dextrose is included as a way of providing extra calories to the patient. In fact, even though these dextrose solutions are hypertonic, once the dextrose is absorbed by the body then only pure water or saline is left in the blood vessels. These three solutions are primarily used for the purpose of providing the patient with extra calories.
3% saline is typically used to treat severe cases of hyponatremia (low sodium). This makes sense because if your blood stream has become hypotonic and it’s supposed to be isotonic, then adding a hypertonic solution will help increase the electrolyte imbalance back to normal levels. Even so, though, you need to infuse the IV solution very slowly and cautiously, and watch the patient closely for any evidence of intravascular overload (aka too much fluid in the blood vessels). This could be increased blood pressure, pulmonary edema (aka fluid in the lungs), or even hypernatremia.
Hypertonic solutions can also be useful for a patient who needs electrolytes but is already on fluid overload, such as in Heart Failure or severe edema. That way you are providing the patient with needed electrolytes, but minimizing the extra water that their condition doesn’t get worse.
I hope this gives you a better understanding of hypertonic IV solutions! Now please leave a comment below telling me how cool you think my shrunken egg is. 🙂 And of course, you can ask questions about this topic, too!