Isotonic vs hypotonic vs hypertonic

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Specializes in med/surg, OR, PACU.

Can someone clarify the difference between the three types of IV solutions and give examples of when you would use each?

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No, do your own homework or Google it.

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Specializes in Critical Care.
SonorityGenius said:
No, do your own homework or Google it.

It doesn't ornurse is a student (previous post -"I've been a nurse for 7 years"), even if she was there are more civil ways to answer that.

OP - you might find this helpful:

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Specializes in ED, OR, SAF, Corrections.

All have to do with manipulating osmosis, which is the movement of fluid (specifically solutes as in salts like Na+Cl- and KCl-) across a semi-permeable membrane from an area of lesser to greater concentration. It helps if you remember that salt always follows water - so think where it is you want that water to go and you'll arrive at your answer as to what you'd treat with what. Ideally, extracellular and intracellular balance is maintained in healthy individuals, but get sick or injured and the balance can get thrown out of whack.

Hypotonic - solution has less sodium than that of the patient's currently circulating plasma. Would be used to push fluid from the vascular spaces into the cells. Too much and the cells will explode. Will decrease circulating volume, so you'd use it when you don't want increased pressure like cerebral edema, or in a dehydrated patient with very high electrolytes, etc...

Isotonic - has same sodium concentration of plasma. Use to replace volume in cases of blood loss, or to maintain hydration. No fluid shift between vascular spaces and cells - they're equalized.

Hypertonic - has a greater concentration of sodium than circulating plasma. Pulls fluid from the cells into the vascular spaces. Too much and the cells will crenate or shrivel up like prunes. Will rapidly expand circulating volume and might be used to treat bad burns, septic shock, etc...

Hypo and Hyper tonic solutions should be used carefully and patient observed for signs that treatment has progressed beyond the theraputic response.

Hope that helps a little. Sometimes it helps if you don't try to memorize things as much as to stop and think what is actually going on and then use your logic (and certain basic concepts you DO need to memorize) to determine what's needed to fix whatever it is that's going on. You're never going to be able to memorize everything you'll go insane trying. Using your critical thinking skills is vastly superior over rote memorization because memory only takes you so far. But critical thinking will help you react to those weird things that come at you from left field.

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Specializes in ED, OR, SAF, Corrections.

Oh, sorry - I just saw the previous post that you're not a student, didn't mean to lecture. Don't feel bad, I've been doing this for 20+ years and there are still things I get hung up on and have to stop and think 'now how does that go again?'

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Specializes in med/surg, OR, PACU.

SonorityGenius:

That was a very nasty way to respond to my post, if you didn't want to answer than just don't! I thought this was a site to help each other out, not tear each other down. i'm not a student, I've been in a specialized field for 7 years. I was asking the question because sometimes its easier to comprehend something when people put it in laymans terms! I have googled and was just looking for some clarification.

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Once a student asked this question (2006) and VickyRN gave this response: I thought is so very helpful!

Tonicity refers to the solute concentration of a solution outside a cell and its effect on cellular fluid volume. The osmolarity of the solution determines the direction of water flow into or out of the cell. In normal body situations, solute concentration within and outside of the cell is usually nearly the same (isotonic).

Isotonic: Same osmolarity as the cells (270 - 300 mmol/L). Equal solute and water--exact same number of particles in both solutions--no net movement of water. Does not change cell volume.

Higher solute concentration surrounding cells pulls water out of the cells. Hypertonic: higher osmolarity than cells (> 300 mmol/L). Greater solute, less water--water moves out of cells. The cell will shrink.

Lower solute concentration surrounding cells causes water to move into the cells. Hypotonic: lower osmolarity than cells (

Isotonicity. If the concentrations of electrolytes are the same in the cell and surrounding fluid, the situation is balanced (homeostatic). The cell fluid volume remains the same.

Hypertonicity: The cell will shrink (crenation) by loss of its fluid to the surrounding hypertonic environment. High osmotic pressure of surrounding fluid pulls fluid out of the cell.

Hypotonicity. In a hypotonic environment, fluid will enter a cell and cause it to swell and burst. The inside of the cell has higher osmotic pressure than the surrounding fluid, so fluid is drawn into the cell.

Both hypertonicity and hypotonicity in the extracellular fluids will destroy cells.

Need isotonicity for cell homeostasis, for balance.

½ NS IV is hypotonic relative to cells. Fluid moves from the vascular space into the cells. When a liter of ½ NS is administered intravenously, it will go into the cells and very little will remain in the blood vessel (since it is hypotonic).

If you put two isotonic solutions side by side, no fluid shift occurs. A liter of normal saline or Ringer's lactate is limited to the extracellular space and will expand the blood volume.

5% Dextrose in NS is hypertonic compared to cells; pulls water into the vascular space from the cells or interstitium.

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Remember, them that has gets.

The area that has the most salt (solutes) is going to get more water... water will always follow the solutes around.

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Specializes in med/surg, OR, PACU.

MunoRN: Thank you for your comment in my defense and thank you for the link, it was very helpful:)

Anisettes: You have nothing to apologize for, i found it very helpful! Thank you again ?

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Specializes in med/surg, OR, PACU.

Thank you very much for your response, it was very helpful!

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Specializes in Trauma ICU.

No offense intended to anisettes, but isitpossible's explanation is more accurate.

Hypotonic - solution has less sodium (as was stated later by @Isitpossible, tonicity is about solute, though na is the greatest component in osmolarity of the human body, it is not necessarily the best way to think about it...think solute. Also, I deleted this part from above but water follows sodium in general, not the other way (in the human body that is) and that is what makes the choice of a solution so important. If i give a hypotonic solution (d5 for example) the water in the solution will "attempt" to equalize the osmolarity across membranes (water generally flows freely across membranes....a few exceptions such as parts of the kidneys...but sodium and other ions require help in some form or another [active transport and membrane proteins that act as channels] to cross cell membranes) and since water moves freely the area with the higher osmolarity (the inside of the cell now that i added water to the outside) will attract the water and thus cause the cell to swell.) than that of the patient's currently circulating plasma. Would be used to push (minor point here but the water is being pulled into the cell) fluid from the vascular spaces into the cells. Too much and the cells will explode. Will decrease circulating volume, so you'd use it when you don't want increased pressure like cerebral edema (this is the major reason i responded and did not just let this all go because it is mostly somewhat academic. The lesson that needs to be heard is that you do not ever give hypotonic solutions to patients with cerebral edema, the cellular swelling can be very detrimental to the pt's icp and any possible vascular decrease will be outweighed by the cellular edema. In fact, you give patients with high icp's hypertonic solutions to draw water from the cells to reduce that portion of the cerebral mass...no room for an icp discussion here), or in a dehydrated patient with very high electrolytes, etc...

Isotonic - Has same sodium concentration of plasma. Use to replace volume in cases of blood loss, or to maintain hydration. No fluid shift between vascular spaces and cells (again a minor point but it would probably be better to think of it as there is no/minimal fluid shifts between the extracellular space and the cells...again minor but the interstitial space needs to be accounted for in these equations)- they're equalized.

Hypertonic - Has a greater concentration of sodium than circulating plasma. Pulls fluid from the cells into the vascular spaces. Too much and the cells will crenate or shrivel up like prunes. Will rapidly expand circulating volume and might be used to treat bad burns, septic shock (again, somewhat minor, but use of hypertonic solutions in these circumstances are generally, at least in the us, saved for prehospital and battlefield wounds. In the hospital you would almost certainly be use ns/lr for these patients because the benefit of hypertonic solutions is quickly lost and become damaging once intracellular and interstitial volumes start to become depleted. You also would end up with ridiculously high na concentrations in the blood which is not good. As a note, most all of what i am saying is based on us practice and there may be differences in other countries.), etc...

Hypo and hyper tonic solutions should be used carefully and patient observed for signs that treatment has progressed beyond the theraputic response could not agree with this statement more. People tend to take more care with hypertonic solutions but too often it seems that we overuse d5 especially..

As an aside, this makes me think of a great set of podcasts I have listened to in the past that might help with this and a number of other tricky subjects. The podcast is icu rounds and is by dr. Geoffry (jeffery?) guy who is the director of the burn center at Vanderbilt University. Very informative and very good. Again, no offense is meant by my response but i felt the need for some minor disagreement. Of course if anyone feels that i have said something wrong please feel free to correct me, i'm always interested in learning.

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Turd Ferguson said:
Remember, them that has gets.

The area that has the most salt (solutes) is going to get more water... water will always follow the solutes around.

Frickin awesome. all these years, and THAT makes sense to me.

Muchas gracias.

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