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!
Osmosis Results Part 1 (from left to right) Hypotonic solution, Isotonic solution, Hypertonic solution
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.
Water leaves the RBC in an attempt to dilute the hypertonic fluid around it
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:
- 10% Dextrose in Water
- 3% Saline
- 5% Dextrose in 0.45% Saline
- 5% Dextrose in 0.9% Saline
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!
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I’m a nursing student, studying for our fluid and electrolyte balance test, I was having a difficult time understanding pressures, osmosis, balance, etc. I’m really glad I found your site and your egg experiment, I’ll always think of that shrunken egg when I hear osmosis! Thank you
That’s awesome! Glad I could help. I loved my shrunken egg…it felt so weird, too! Hope your F&E exam went well!
Amazing explanation. Perfect! I also have a test but now I completely understand it. Thank you so much you should have been my professor!
Yay! So glad I could help. I love teaching, and wish I could be EVERYONE’s professor!
Thank you so much for your explanation. This is a confusing concept to grasp. Your experiment makes it much more understandable!
Hypo/Hyper-tonicity can be really tricky to understand, but it’s so important because it involves osmosis and diffusion. If you can understand this now, it makes it much easier to understand and remember symptoms of diseases you’ll study in the future, too!
I had a question regarding the statement for hypertonic solution being ok to give to patients with heart failure and severe edema. In our handout from the instructors it states that if a patient is on a fluid restriction and has impaired heart or kidney function the hypertonic solution will expand the intravascular compartment putting extra strain on the vascular system so do not administer… Im confused.
Good question, Heather!
What you saw on your handout is generally true…hypertonic solutions should not be given to most patients with heart/kidney dysfunction because it CAN cause water to want to enter the blood vessels in order to “dilute” the hypertonic solution. This would lead to even more fluid overload, which the malfunctioning heart/kidneys would have a tough time handling.
What I’m talking about in this article, though, is a slightly different scenario. If you have a patient with heart/kidney dysfunction who ALSO has low electrolytes, then you need to find a way to replace the electrolytes without causing fluid overload. That’s where the hypertonic solutions can be given to these patients because they are heavy on the electrolytes but relatively lighter on the fluid. That means they can provide a lot of electrolytes with relatively little added stress on the circulatory system.
I hope that clears it up for you!
Thank you so much! I am in my first semester of nursing school and we are studying Fluid and Electrolyte balance. This helped me! If you aren’t a teacher, you should be!!
Your welcome! So glad it helped. Even though I’m not a “traditional” teacher at a school, I love how the internet gives me the opportunity to be a teacher to way more students then I could reach in a single classroom. Good luck with the rest of your semester!
Excellent site. It is worth mentioning that rapid correction (more than .5meq/L/hr) of hyponatremia (via hypertonic saline or ADH antagonists) can lead to central pontine myelinolysis aka osmotic demyelination syndrome which is characterized by dysarthria, dysphagia, and paralysis.
Thanks for adding the additional info!