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Really need help with electrolytes and fluids


I need help! My test is next Monday and it is supposed to be the hardest of the semester! I am learning about F&E and our professor told us to just focus on potassium and sodium. I am having trouble understanding Hypo/hypernatremia and hypo/hyperkalemia. I heard from previous nursing students that the F&E tests have scenario questions and that I really need to be on top of my game for this. I need to know symptoms, causes, interventions and all the important things of these electrolytes. Does anyone know of any valuable resources that help in understanding those two electrolytes? I have looked in many places and still cant seem to grasp the concept. Also does anyone know of any good websites that have practice questions so I can prep myself into what they are looking for in the questions?

Esme12, ASN, BSN, RN

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma. Has 41 years experience.

There are 6 major electrolytes. Sodium, potassium, calcium, chloride, magnesium and phosphorus. It is primarily potassium, calcium and sodium that will cause problems when they are out of whack.

  • hypokalemia
  • hyperkalemia
  • hypocalcemia
  • hypercalcemia
  • hyponatremia
  • hypernatremia

When there is a sodium imbalance quite often there will be changes in mental status - confusion, delirium, etc. Often seen with traumatic brain injury where diabetes insipidus (pathological voiding of large amounts of dilute urine) and its opposite SIADH (syndrome of inappropriate antidiuretic hormone - minimal urine output but very concentrated) may occur. Sodium imbalances are also seen with dehydration in some patients (elderly, burn victims, many others) and the blood levels will go up. Very rarely, sodium levels in the blood will go down because of consuming large quantities of fluids.

The other main electrolyte imbalance seen is when potassium is out of whack, and its most serious consequence is cardiac problems that can be life-threatening (you will see T wave changes: depression with hypokalemia, elevation with hyperkalemia, among other changes in the EKG like QRS interval changes).

For these 2 main electrolyte imbalances remember: Sodium equals mentation, and Potassium equals cardiac.

Sodium does affect fluid. In fact, they say sodium always follows water. There are a lot of people with edema related hypernatremia; and a lot of dehydration related to sodium and chloride losses. Potassium tends to affect the heart and in the clinical area you will see dramatic instances of people with hypokalemia and hyperkalemia. Calcium affects the muscles and is not as commonly seen clinically because it is detected because of lab testing.

  • Sodium - body water balance
  • Potassium - contraction of skeletal and smooth muscle and nerve impulse conduction
  • Calcium - formation and structure of bones and teeth, cell structure and function, cell membrane permeability and impulse transmission, the contraction of all muscle types and is necessary in the blood clotting process
  • Chloride - important in the digestive acids; closely linked to sodium
  • Magnesium - affects nerve and muscle action by affecting calcium usage, activates enzymes involved in carbohydrate and protein metabolism, helps in the transport of sodium and potassium across cell membranes, and influences the levels of sodium, potassium, calcium and some body hormones (parathyroid hormone)
  • Phosphorus - formation and structure of bones and teeth, this electrolyte is needed in the following activities: utilization of B vitamins, acid base homeostasis, bone formation, nerve and muscle activity, cell division, the transmission of hereditary traits, metabolism of carbohydrates, proteins and fats
  • http://www.elmhurst.edu/~chm/vchembook/253fluidkidneys.html

Third-spacing: Where has all the fluid gone?


table of commonly used iv solutions.doc





Edited by Esme12

Na+ and Water Balance, or why you have to remember that serum sodium doesn't tell you anything at all about sodium :), and that saline is not water and salt.

OK, thought experiment time: Draw pictures with little molecules or such if you like, it will help. You have a beaker full of salt water, with a Na+ level of, say, 140 (hmmmm, what a coincidence). You pour half of it out. What is the Na+ level in the remainder? Right, 140, because that measurement is a measurement of CONCENTRATION, not a count of the absolute number of sodium molecules. Got that? If not, work on it, because you have to "get" it.

Now you refill the beaker to its previous level, full up, with plain water... or, say, D5W, which is the same thing, physiologically. Now what's your sodium level? Right, 70, because you have twice as much water per amt of sodium.

Go back to the half-full beaker again, the one with a serum (oooh, a Freudian slip! I think I'll leave it. Serum counts as saline.) sodium of 140. Fill it up with an equal volume of....normal saline, which for purposes of this discussion has a sodium level about the same as blood serum. What's the serum sodium now? Right, still 140. As a matter of fact, you can pour quite a bit of NS into a body and not really influence the serum sodium that much at all. The way you change the serum sodium is by changing the amt of WATER.

Repeat to yourself: "Serum sodium tells you about water balance." and "Saline is not sodium and water." (I used to have a poster of this and have my classes chant it three times before going on :) ....I wanted to be sure they would remember it for later)

OK, deep breath. Now we look at water balance from the other side.

Saline pretty much stays in its vascular place (unless you cut a blood vessel and spill some out). But water....ah, water travels. As a matter of fact, that's the other poster. Repeat three times: "Saline stays, water travels." (think: rivers flow from place to place, but the ocean pretty much stays where it is.) What the heck importance is that?

Back to your original beaker.... the one full of stuff with a serum Na+ of 140. Evaporate half of the water. What is the serum sodium now? Right, 280 (whooee, bigtime dehydration) As a matter of fact, if you lose enough water from your body to get your serum sodium up to 170 or so (("Serum sodium tells you about water balance")), you'll probably die, especially if you do it rapidly. Why? Because water travels in and out of all your cells. If you lose water from your intravascular space, sweat it out, or pee it out because your kidneys are unable to concentrate urine for some reason, thus making your bloodstream more concentrated, water molecules on the other side of the cell walls all over town say, "Whoops! Gotta go!"...because water travels across cell membranes from an area of more water per volume (lower salt concentration) to the area of less water per volume (higher salt concentration). So if you are de-hydrated, meaning water-poor, all your cells shrink. Most importantly, if your brain cells shrink enough from water loss, they pull away from your pia mater/meninges and you have an intracerebral bleed. Bummer.

(Interestingly, this is why you have a headache with your hangover after an alcohol binge. Alcohol temporarily disables your kidneys from retaining water well, so they let too much out. You pee a lot, and your brain shrinks just enough to put a little tension on your pia mater/meninges. Bingo, headache.) (Ahhh, digressed again....)

OK, now put this all together and tell me why your hematocrit is a lousy indicator of water balance (as a matter of fact, a nigh-on USELESS indicator of dehydration), but a good indication of saline balance.

OK. You are walking down the street with a perfectly good crit of 40 and a serum sodium of 140 (and normal other lytes). You are accosted by someone with a sharp thing and before you know it, a whole lot of your circulating volume is running into the storm drain. Fortunately, you are whisked into a nearby ER immediately, having had your bleeding stopped by a nearby Boy Scout with good First Aid Merit Badge training (ummmm, I teach that too). The ER nurse draws a baseline crit and lytes. What are they?

OK, crit is still 40...because hct is a *percentage of the blood that is red cells*, not a count of the absolute number of red cells you have. So even if you lose a lot of your blood, your crit is unchanged. Until they start fluid-resuscitating you with.... normal (not half-normal) saline (or RL, which acts like it for purposes of this discussion).

Na+ is still 140, because you have lost saline (serum counts as saline) but not water.

Thought experiment time again. Take two tubes of whole blood, that is, serum and red cells. They both have a Hct ( which is often spoken as “crit”) of 40, that is, 40% of the volume of each tube is taken up solely by RBC's. We already know what happens if you add saline to one of them: the crit drops, right? But what happens to the crit of a tube of blood if you add water-- like D5W? Answer: Nothing. Why? Because the crit is a % of volume....and when you add water, the water travels into the cells too. So they swell up, and their %age size change means no change in the crit of the tube. They still take up (in this example) 40% of the volume. What happens if, instead of adding water to your original tube of hct=40 blood, you evaporate half of the water out of it? (The answer is NOT, "Make gravy." Shame on you.) No, the hct stays the same, because the cells lose water too, and they shrink as much as the liquidy part did. Same percentage of red cells in the resulting volume = no change in hematocrit.

So. When you have someone dehyrated (as evidenced by their elevated serum Na+), you give him water (or D5W). This dilutes his serum Na+ back towards normal and allows his shrunken dehydrated cells to regain their girlish plumpness. Normal saline will not help, as it will not change the serum sodium level ("Saline is not sodium and water") and will not move into cells to restore their lost water content ("Saline stays, water travels.")

If you have someone who is hypovolemic, as evidenced by (hmmm? what? how do you assess hypovolemia? How about BP, CVP, JVD, PAd, LVEDP, etc? You pick 'em), you give him saline, which goes into his vascular space where you want it for circulating volume but doesn't go anywhere else. D5W will not do the job, as it will travel into cells (not just RBC's, but all cells, and most of it will thus not be available in the vascular space to make blood pressure).

So why do dehydrated old ladies have high crits AND high serum Na+'s? Well, as I was fond of telling my students, it's perfectly possible to have two things wrong at once.

Let's look at a couple of people and see if that helps.

1) Serum Na+ 140, Hct 25, BP 110/60. OK, so this guy is relatively anemic, but his circulating volume is OK (as evidenced by an adequate BP) and his water balance is fine (as evidenced by his normal Na+). Who does this? Well, anemia can have many causes, but if he comes in with a hx of a recent bleed with fluid resuscitation, you could guess that he had a perfectly good crit until he lost some red cells out his GI bleed or stab wound or bloody ortho surgery or something, and we were stingy and just gave him NS back. His crit is called "dilutional," as in, "His red cells are floating in saline."

2) Serum Na+ 118, Hct 40, BP 110/60. This guy has 'way too much water on board, as evidenced by his Na+ that's 'way low ("dilutional" too). We call him hyponatremic, but it's not that he has lost sodium (in most cases), it's that he retained too much water. He hasn't lost saline, as evidenced by his decent BP ("Saline is not sodium and water"). Who does this? Well, remember the dread "SIADH"? "Syndrome of inappropriate antidiuretic hormone"? Lessee.... inappropriate, ummm, too much. Antidiuretic, ummmm, doesn't allow diuresis, holds onto water.... Bingo. He's retaining water, and his Na+ is called "dilutional" because all those little Na+s are floating around in too much water. Some degree of SIAHD is actually pretty common--- you can do it with anesthesia, mechanical ventilation (there's stretch receptors in the lungs, see, and....oh, later), and a host of common meds. Of course, you can also get a low serum sodium in a hurry if some fool tanks you rapidly with a liter or two of D5W, or , like that poor woman in a SoCal radio contest, you drink a ton of plain water over a short period of time. She died of acute cerebral edema when her brain swelled up faster than her skull would stretch to accommodate it.

Hope this makes some level of sense. More?

Wow. I am not a nursing student, (yet), but this lesson in fluids chemistry was great! A very enjoyable read, and you have a sense of humor. Where do you teach because I want to go there! If I get my prereqs done and get accepted into nursing school, I hope I get a teacher like you.

Gee, thanks. It's what we do for fun :) Esme and I are collecting "likes," LOL.

Esme12, ASN, BSN, RN


Thats right....now remember to hit our like buttons!!!! :)

i like you all posts!

hodgie RN - the Fluid and Electrolyte Imbalances is "DA BOMB". Thank you.:yes:

Thanks for this! I'm working on a care plan with a pt with hyponatremia, cirrhosis, etc. this helps a lot!


Specializes in Geriatric.

GrnTea's explanation was copy and pasted into a word document on my laptop for easy access during school. She's a lifesaver.


Specializes in OB.

How can I print this awesome information?

How can I print this awesome information?

You copy and paste it into a word processing document, same as anything else!

i copied tea's post!!!!!! immediately

Thank you all so much for breaking down the different types of solutions in easy to understand terms. I am a new graduate, getting ready to take the NCLEX and am really struggling with the fluid and electrolyte concepts. To boot, I got a job in the ER to start after I pass the test and am somewhat intimidated at the thought of having to know all of this, especially in an emergent situation. Just when I think I've got it, I fear not being able to act on it quickly. Any ideas?


Did you read those posts above, the ones with a bazillion "likes"? You will certainly see people with hyponatremia and hypernatremia in the ER. You'll see hyper- and hypokalemia too. Remember: most sodium is outside the cells, so serum Na+ is the big number. Most potassium is inside the cells, so serum K+ is the small number. (There are two letters in Na and one in K, if that helps you remember that).

Short and sweet, quick and dirty:

Serum sodium tells you about water balance, as above.

The biggest effect of potassium derangement is on muscles...and what's the most important muscle in your body? Bingo, cardiac. So what happens when serum K+ is low and so K+ wants to leave the cardiac muscle cells? What do they do? They get twitchy, that's what. Tachyarrythmias (like PVCs)...


I'm sorry "big number?" are you talking about the range? I'm not trying to be a dummy, but I have so much info in my head, I am struggling to make it all make sense. I am hoping so that it all starts to come together. Right now I feel like I only know a couple of ranges, and some consequences of potassium (heart), sodium (neuro), calcium (bones).


Specializes in None yet..



There will be other more critical problems long before the bones are involved! Calcium blocks sodium channels and inhibits depolarization of nerve and muscle fibers; low calcium levels lower the threshold for depolarization. Remember the symptoms with "CATS go numb"- Convulsions, Arrhythmias, Tetany and numbness/parasthesias in hands, feet, around mouth and lips.