Hypertonic IV Solutions

by Nicole on July 1, 2012

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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{ 37 comments… read them below or add one }

Myrranda Essex January 30, 2013 at 10:57 pm

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 :)

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Nicole February 11, 2013 at 10:25 pm

That’s awesome! Glad I could help. I loved my shrunken egg…it felt so weird, too! Hope your F&E exam went well!

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Nursing student (feels like eternity) February 18, 2013 at 3:42 am

Amazing explanation. Perfect! I also have a test but now I completely understand it. Thank you so much you should have been my professor!

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Nicole February 19, 2013 at 8:20 pm

Yay! So glad I could help. I love teaching, and wish I could be EVERYONE’s professor! :)

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jennifer February 20, 2013 at 7:40 pm

Thank you so much for your explanation. This is a confusing concept to grasp. Your experiment makes it much more understandable!

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Nicole February 20, 2013 at 9:34 pm

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!

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Heather February 23, 2013 at 9:18 pm

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.

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Nicole February 24, 2013 at 9:20 pm

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!

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Sarah February 25, 2013 at 10:05 pm

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!!

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Nicole February 25, 2013 at 10:22 pm

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!

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Ali April 21, 2013 at 12:37 am

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.

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Nicole April 22, 2013 at 9:31 am

Thanks for adding the additional info!

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Nicole Gravelle June 27, 2013 at 4:39 pm

Your article is very interesting .I have cystic fibrosis and I am on a treatment witch consists of inhalations of hypertonic 5% saline solutions by nebuliser, Can you tell me more on this?
Thank you.

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Nicole July 14, 2013 at 5:28 pm

Definitely talk to your dr as s/he should be making sure that you understand the rationales for all your treatments (and I am not in a position to be giving anybody medical advice!).

But I would guess that it has something to do with keeping your airway well hydrated and moist so that the mucus stays looser and is easier to cough out…kind of the same rationale as putting a humidifer in someone’s room when they have a cold.

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John Zes August 6, 2013 at 3:47 pm

I could still use a little clarification on how hypertonic solution can help with fluid overload. Thank you for the great column

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Nicole August 8, 2013 at 11:26 am

Basically, it patients with certain conditions, it can help by pulling fluid out of the tissues (edema), and back into the blood vessels. Once the fluid is back in the blood vessels then the extra fluid can be filtered by the kidneys and peed out of the body.

Hope that helps clarify!

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Elizabeth September 12, 2013 at 5:35 pm

How exactly does a hypertonic solution cause pulmonary edema?

Thank you! Great explanation! Studying F&E now :-)

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Nicole September 12, 2013 at 10:15 pm

Whenever you have severe fluid overload in the blood vessels, the pressure in the vessels can become so strong that it starts pushing fluid out into the interstitial space. This is especially true in the smaller capillaries, such as in the lungs. And when the fluid leaves the capillaries in the lungs, then you get pulmonary edema. So really, you can think of it as a result of increased BP, which is one of the first things you would be watching for anyway.

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Graxia November 21, 2013 at 5:21 pm

For burn cases, which solution should we give, hypertonic or hypotonic? Since the body would get extremely dehydrated I think hypotonic should be given? What particular type of I.V. it would be? I’m currently doing my self-review for NCLEX, I want to make sure I didn’t forget my college learnings. Thank you Nicole :)

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Graxia November 21, 2013 at 5:24 pm

Oops nope, burn will cause fluid shift so the cells will swell therefore we need to give hypertonic for the aid of those cells. I’m a bit confused.

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Nicole November 24, 2013 at 9:24 pm

Actually, an isotonic solution such as Lactated Ringers is usually given for burn patients. The goal is to get the patient rehydrated as fast as possible to prevent or at least reverse hypovolemic shock that often occurs as a result of burn injury. That’s also why they will often put in two large bore IVs upon arrival at the hospital, or even insert a central line in some cases.

Keep thinking things through, but don’t try to make it too complicated! :) The ultimate goal for fluids in a burn patient is simply to make sure they have enough fluid in their blood vessels.

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Liz December 6, 2013 at 2:20 pm

I like how simply you put the process.

I originally found this article while looking around online for help with a question regarding the physiologic reaction to fluid administration… I am having a hard time finding a site that explained the difference between the administration of hypertonic solutions for replacement vs dieresis… but more specific than a definition…

…does it first work by replacing any lost solutes then if administration is continued it begins to pull water/fluids from ISF/ICF.?. …or do the solutes in the administering bag dictate which operation is done.?.

any help would be appreciated

(…I have the same confusion with hypotonic solutions…)

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Nicole December 17, 2013 at 11:13 pm

Hi Liz,

Since the body is so complicated, it’s not going to be a completely cut and dry process, meaning that the IV fluid isn’t going to first do one thing, then stop doing that to do another thing. It will be more of a gradual progression depending on the current balance of fluid and electrolytes. It’s one of the ways the body tries to maintain homeostasis.

That being said, when a hypertonic solution is administered then the electrolytes in the blood vessels will increase. As they increase, they encourage water from outside of the blood vessels to enter the blood vessels through osmosis. Some of this water can be from RBCs or other cells that you don’t necessarily want losing fluid, but usually the electrolyte lab values (especially sodium) will be abnormally high before that happens. Then as more and more fluid enters the blood vessels, the blood pressure will increase. And increased blood pressure is a big factor in how much urine healthy kidneys can output: the higher the blood pressure, the more urine created.

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lorde January 10, 2014 at 7:49 am

You provided great information for me to use to back up my argument as to why diabetic patients excrete so much water in the form of urine and sweat, and also why they take in more water.
Thank you
lorde
student dietician
http://www.baronlordeblinks.webs.com

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Kara March 21, 2014 at 4:06 am

I’m a PICU nurse, trying to better understand one of my patient’s “cerebral salt wasting” condx and the need for 3% Saline. This was very helpful!! Thank you!!

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Barbara April 6, 2014 at 7:46 pm

Would this be used for a sickle cell crisis?

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Nicole April 7, 2014 at 10:01 pm

Good question, Barbara.

No, you would definitely NOT want to use this for sickle cell crisis. With sickle cell, the RBCs are already abnormal (in the sickle shape). Plus, when a patient gets dehydrated it can trigger a sickle cell crisis. So one of the nursing actions is going to be to do things that support hydration for a sickle cell patient. In most cases, those patients will get an isotonic IV solution. Just picture in your head that you’re filling their blood vessels up with more fluid so that the sickle shaped RBCs have more room to float around and are therefore less likely to get “stuck.”

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Sumayya Samreen May 5, 2014 at 1:20 pm

When a medical patient needs to have additional fluids injected into their veins in order to increase blood volume, should the nurse use pure distilled water or isotonic solution?

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Nicole May 5, 2014 at 4:50 pm

In most cases, isotonic solution is used to increase blood volume.

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Arlene May 8, 2014 at 11:26 am

I am having trouble understanding how TPN does not dehydrate the patient. Since TPN is hypertonic, wouldn’t it pull fluid from outside the blood vessels causing dehydration and FVO?

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Nicole May 19, 2014 at 1:12 pm

Since TPN contains all the nutrition the body needs (protein, fat, carbs, etc), then those things don’t stay in the blood vessels long enough to attract a lot of water. Instead, they leave the blood vessels and go into the body cells where they are needed. That’s why TPN typically won’t cause a fluid imbalance.

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MJ May 23, 2014 at 1:09 am

This might be an odd question but I was learning about hypernatremia and it said that it causes peripheral edema. While trying to figure out why that was so, I came across this post. Now when I think of hypernatremia, I think of a hypertonic solution. Which is why I don’t understand why it would cause peripheral edema. When I think about it simply, I understand that the increased solute in the vessels will cause the fluid to shift out of the cells… but I thought it would go into the vascular space thus increasing blood pressure instead of sitting in the interstitial space. Is that right? Can you explain more succinctly why hypernatremia causes peripheral edema? Thanks in advance!

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Nicole May 29, 2014 at 10:31 am

Good thought process! When you dig into hypernatremia a little bit more than I did in this article, you see that the fluid shift is not only about the blood vessels. Another major factor going on is that the fluid is leaving the CELLS to help dilute the hypernatremia in the blood vessels. So individual cells throughout the body are getting dehydrated (like my shriveled little egg in the picture). Hypervolemia is the body’s attempt to dilute the solute in the blood vessels enough to prevent problems from the hypernatremia. Once the sodium is diluted enough to slow down or stop pulling water into the blood vessels, then excess water can continue to accumulate in other areas of the body. Also, there’s so much water moving from inside the cells to outside the cells, that it’s not all going to get into the blood vessels immediately…it will gradually move there via osmosis, but in the meantime there will be edema.

Of course, this is still partly a simplification, because this is not a one-way process (the water leaves the cells and goes directly to the blood vessels to dilute sodium). There’s always a “back and forth” going on as water moves in and out of cells AND blood vessels in an attempt to reach homeostasis.

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zuhra August 4, 2014 at 4:08 pm

really cool :)
That blood vessel and the other spaces are the most important to take into consideration because it is confusing when one only thinks of rbi or cells…

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Kim Houston July 22, 2014 at 5:44 pm

What a relief to find someone on the Internet who actually has the facts straight. I’m beginning to get a grasp on things by reading your posts. I noticed that some of them are 2013. Are you still available?
Thank you so much.
Kim Houston

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Wendy August 2, 2014 at 7:28 pm

You are so awesome!! Thanks for explaining this !!!

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zuhra August 4, 2014 at 2:55 pm

For me personally; this was always a really easy topic in general chem class , but applying this concept into practicality and nursing makes it complicated and worth to ponder about…..
You are really nice to do this, I wish there were more nurses like you ! :)

Thank you.

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