Fluid/Electrolyte question

Nurse Kyles, BSN, RN · Feb 2, 2011

I am a third semester student and am just learning about fluid & electrolyte imbalances as well.

To understand it all better, I have been using Medical-Surgical Nursing Made Incredibly Easy. It has been SUPER helpful. This is from page 47 of that book:

"Isotonic

Isotonic fluids, such as normal saline solution, have a concentration of dissolved particles, or tonicity, equal to that of intracellular fluid (ICF). Osmotic pressure is therefore the same inside and outside the cells, so they neither shrink nor swell with fluid movement.

Hypertonic

Hypertonic fluid has a tonicity greater than that of ICF, so osmotic pressure is unequal inside and outside the cells. Dehydration or a rapidly infused hypertonic fluid, such as 3% saline or 50% dextrose, draws water out of the cells into the more highly concentrated extracellular fluid (ECF).

Hypotonic

Hypotonic fluids, such as half-normal saline solution, have a tonicity less than that of ICF, so osmotic pressure draws water into the cells from the ECF. Severe electrolyte losses or inappropriate use of I.V. fluids can make body fluids hypotonic."

I hope this helps you! Good luck!

(Springhouse. Medical-Surgical Nursing Made Incredibly Easy!, 2nd Edition. Lippincott Williams & Wilkins p. 47).

BacktotheBeach, ADN, BSN, RN · Feb 2, 2011

I second the above info. I would definitely get Fluids and Electrolytes Made Incredibly Easy. It is a lifesaver! I think you will use it in the future, too. It breaks down lots of other tough concepts.

ImThatGuy, BSN, RN · Feb 3, 2011

It's got everything to do with osmotic pressure. To grasp any of it you'll need a solid understanding of osmosis, diffusion, osmotic pressure, osmolarity, osmolality, hydrostatic pressure, filtration, facilitated diffusion, colloids, etc.

Go to my posts and dig around in my history for a post titled something like pathophysiology help. I wrote about a page trying to teach all of it to a lady. See if any of that helps, and I'll be happy to answer other questions.

By the way, they'll teach that 5% dextrose and water is isotonic as well, and it is. However, it quickly becomes hypotonic as the dextrose becomes metabolized. In some books you'll see it listed as hypotonic. A decade ago in paramedic school we were taught that D5W was a hypotonic solution. That's just another nugget to help you.

Once you get down what I mentioned in my first paragraph you'll love it. I do.

Turd Ferguson · Feb 3, 2011

Memorizing it is not that hard- remember that ISOTONIC refers to fluids that have a serum osmolarity of 270-300 mOsm/L

Isotonics are technically NS, LR, and D5W (although D5W is not usually used to rehydrate patients as an isotonic fluid... see ImThatGuy's above post)

Hypertonics are fluids above isotonic, so D10W, 2 or 3% NS, OR any isotonic fluid PLUS anything else (D5 in NS, D10 in NS, etc...)

Hypotonics are any fluids below isotonic- D2.5W, 1/2NS, etc

IVRUS, BSN, RN · Feb 7, 2011

koko2002...

First of all, it's important to remember that all solutions and infusion medications are compared to what NORMAL SERUM OSMOLARITY is... which is approx. 290.

For a solution to be considered isotonic, it has to have a similar osmolarity to blood plasma. An isotonic solution can have + or - 50, on either side of 290... So, a solution that is isotonic will have an osmolarity of 240-340. (Look on a bag of IV fluids and usually within the first five lines of the paragraph below what the solution is, it will state its osmolarity), Therefore, anything below 240 will be a HYPOTONIC solution and anything above 340 will be HYPERTONIC.

IF a patient's cells are dehydrated, what kind of solution would be best for him, or her? .... A Hypotonic solution ( Think of this solution as one that has more water than salt) as the fluid will leave the Intravascular (ECF) and travel into the interstitial (also ECF) and the cells (ICF) as the body always wants to get to the state of homeostasis. (ECF TO ICF)

If a person has just lost volume, through N/V for instance, an Isotonic solution may be best. (Think of isotonic as a solution that has an equal amount of salt and water)

But if a person has just come back from OR, and they have third space shifting, or edema outside the blood vessels, a hypertonic solution (think of it as a solution that has more salt than water) will cause fluids to shift from the cells, into the blood vessel whereby the kidneys can remove the excess. (ICF to ECF)

Hope this helps.

Jonathank · Feb 7, 2011

OP: you might benefit from reviewing your A&P. Many of these concepts are introduced when you study the circulatory and urinary systems.

Justmenfl · Feb 8, 2011

I am learning about IV solutions also

I remember IV solutions this way

if it is 0.9 NS(Normal Saline) LR(Lactated Ringer) or D5W=isotonic (D5W becomes hypotonic)

less than 0.9 ie 0.45% NaCl =hypotonic

greater than 0.9 ie 3% NaCl=hypertonic

I know this is pretty simplified but it gives a statrting point

ImThatGuy, BSN, RN · Feb 8, 2011

I am learning about IV solutions also
I remember IV solutions this way
if it is 0.9 NS(Normal Saline) LR(Lactated Ringer) or D5W=isotonic (D5W becomes hypotonic)
less than 0.9 ie 0.45% NaCl =hypotonic
greater than 0.9 ie 3% NaCl=hypertonic
I know this is pretty simplified but it gives a statrting point

D5, 1/2 NS anyone?