Isotonic IV Solutions

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 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.

In a healthcare setting, Isotonic solutions are ubiquitous (that means they’re everywhere).  The definition of “isotonic” for the purposes of nursing is any solution that has approximately the same ratio of solute to solvent that you see in blood.

The most obvious one is 0.9% Saline Solution, better known as Normal Saline.  Normal Saline is given to increase the amount of fluid in the blood vessels (intravascular space), without significantly changing the balance of electrolytes in the body.  This is useful for making sure a patient remains in a well-hydrated state of homeostasis.  Normal Saline also happens to be the only IV solution that can be infused at the same time as a blood product.

I recently observed the dramatic results that Normal Saline can produce.  After I finished recording my Osmosis Experiment, I was curious to find out if the shrunken state of my severely dehydrated egg could be reversed.  So I plunked it into my Normal Saline Solution and waited to find the answer.  It only took a few short hours to discover that the Isotonic Solution easily rehydrated my shriveled egg until it looked like this:

Formerly “dehydrated” egg makes an eggstraordinary comeback

Needless to say, I was as giddy as a school girl!  (As I’ve already mentioned in previous posts…yes, I realize that I am a big nerd :))  I was actually surprised by how quickly the osmosis reaction happened to refill the egg with water, although I suppose I shouldn’t have been.  Isotonic solutions can work pretty quickly in the body, too, to reverse similar problems. Once the egg was rehydrated, I couldn’t tell it apart from the other eggs in my osmosis experiment.

There’s some other Isotonic Solutions that you should be familiar with, too:

  • 0.9% Saline (aka Normal Saline)
  • Ringer’s Solution
  • Lactated Ringers
  • 5% Dextrose in 0.225% Saline
  • 5% Dextrose in Water (technically, Isotonic, but physiology hypotonic…I’ll explain in a minute)

Ringer’s and Lactated Ringer’s Solutions contain a wider variety of electrolytes than Normal Saline, which makes them even more similar to what’s found in blood plasma.  Normal Saline only includes Sodium and Choride (Na+ and Cl).

Quick side note I want to point out:  even though Normal Saline doesn’t contain ALL of the electrolytes found in the blood stream, Sodium and Chloride are by far the most common, which is what makes Normal Saline work so well as an isotonic solution.  To help you remember that, just think about the normal ranges for each electrolyte…sodium and chloride have the biggest normal values (135-145 mEq/L and 96-106 mEq/L, respectively)!

The Isotonic Dextrose solutions have the same goal as the hypertonic Dextrose solutions:  to provide extra calories to the patient.  Remember, Dextrose is just a sugar, which can be easily absorbed by the body and turned into energy.  5% Dextrose in Water is a special case, though.  Although it is technically isotonic, it acts upon the body as if it is hypotonic. The reason is because once the dextrose has been absorbed, there is only plain water left.  Obviously, plain water without anything in it is hypotonic!  So you’ll end up with the same effects that you would see if you had given the patient a Hypotonic IV solution to begin with.

I hope this gives you a better understanding of isotonic IV solutions.  Please leave a comment below to share one new thing that you learned about isotonic solutions!


  1. krisae says

    OMG! that is so cool!!! Thank you for this. I was really struggling with IV solutions in my physiology class. I am now preparing for my finals and now I think I can ace it because of this. 😀 <3

  2. krisae says

    Oh yeah, what’s the difference between intravascular space and intercellular space. Are they components of the ECF?

    • says

      Yes, and the key to remembering that is to recognize the prefixes of each word. “Inter-” means in between, and “Intra-” means inside. So “intravascular” means inside the blood vessels, and “intracellular” would mean inside the cells. But “INTERcellular” would mean between the cells. And fluid that is not inside of the cells would be considered part of the extra-cellular fluid (ECF).

  3. Bobbie Blas says

    You are Awesome with this! I have not ever seen how simple and simply easy you have explained the IV solutions! Thank you..

  4. Avery says

    Just a comment on the purpose of D5W (with your comment that it is just to give the patient extra cals, which it is definitely sometimes used for!) We learned about this in patho last week! As you stated, IV D5W is used for rehydration (instead of, for example, sterile water), and the dextrose has nothing to do with fluid imbalance.

    The dextrose is there, however, not just for calories but simply to protect the patient’s RBCs at the tip of the IV needle. The dextrose in the bag is isotonic; this means that the concentration of fluid at the tip of the needle where D5W is dripping in is isotonic, and the RBCs go happily by. If sterile water were infused, you’d have hemolysis, as at the tip of the needle, the water dripping in would greatly dilute the blood (fewer solutes). The circulating RBCs flowing past the needle tip will swell to the point of hemolysis, which is truly dangerous! So D5W is given to protect the body from destruction of RBCs, not just to give patient extra cals. Just thought it was an interesting note that highlighted the importance of understanding tonicity! Thank you so much for your osmosis experiment…it helps me a lot!

  5. Holly says

    Sorry don’t mean to complain, but before you took the egg out of the ” hypertonic”‘ solution, you referenced it as “hypotonic” . This is such a confusing theory!!

  6. Peter says

    I’m not a nurse but a retired science teacher,and I’ve found that a good way to understand osmosis is to remember that it is about which direction water molecules flow .
    Put simply they flow from a place where there is more to a place where there is less of them.
    That is from where the WATER concentration is greater to where the WATER concentration is less.
    Hope this helps
    Cheers from Australia

  7. says

    Hi! Can i ask?? Upon reinfusion (end of dialysis treatment), Is it compatible to use Dextrose 5% Water aside from Normal Saline in dialysis treatment?

  8. Jija says

    would you be able to help me understand the fluid resuscitation in DKA , NS followed by 1/2 Ns and then followed by d5 1/2 ?NS

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