Confusion on the NA/water relationship

[swnewrngrad]

Ok, I am confused about the sodium water relationship. I thought that I had a pretty good grasp on the concept and made it all of the way through school and then I attended the HURST review and their section on this topic has confused me.... Does nausea and vomiting lead to hypernatremia or hyponatremia? I was under the understanding that NA follows water, but the hurst review states that nausea and vomiting lead to hypernatremia? I'm confused and would appreciate any help.

[Intern67]

I was under the understanding that NA follows water, but the hurst review states that nausea and vomiting lead to hypernatremia? I'm confused and would appreciate any help.

Stop "undertsanding" that sodium follows water and start thinking about what is going on to cause excesses or deficits. My classmates are often similarly confused by the "sodium follows water" axiom. I think it does more harm than good.

Nausea and vomiting lead to hypernatremia because you lose more water than sodium and the patient is unable to drink water to maintain the balance. The sodium doesn't jump out of your body because water is leaving.

[swnewrngrad]

So let me clarify... is NA excreted thought the kidneys as Mg and K+ are?

[ggmugsy]

My A&P teacher drilled into our heads just the opposite, that where sodium goes, water follows.

ANH allows sodium to leave the kidneys, and water follows to lower BP.

Aldosterone is opposite, it retains sodium, at the expense of potassium, (also in the kidney) so water stays in the body.

Vomiting isn't affected by the hormones that normally control water balance so water is leaving the body, but the sodium is not.

[anonymous1919, LPN]

Nausea and vomiting lead to hypernatremia because you lose more water than sodium and the patient is unable to drink water to maintain the balance. The sodium doesn't jump out of your body because water is leaving.

This makes the most sense to me. At first I was thinking... well if they are throwing up, then sodium is leaving as well... But all the sodium in your body doesn't sit in your stomach so just because you are throwing up doesn't mean you're going to be hyponatremic. Throwing up leads to hypovolemia so now you have more sodium in your cells and less water which= hypernatremia.

Edit: Is my line of thinking correct here?

[ggmugsy]

I think . . . YES! :)

[swnewrngrad]

Sounds good... In DI when the water is leaving is the same situation as vomiting... where only the water is leaving but the NA is not?

[ggmugsy]

I would think so. My A&P teacher must have said it 10,000 times . . . "Where sodium goes, water follows." Seriously, I still hear it in my dreams. lol

[anonymous1919, LPN]

I would think so. My A&P teacher must have said it 10,000 times . . . "Where sodium goes, water follows." Seriously, I still hear it in my dreams. lol

This sounds more like your A&P teacher talking about fluid shifts with in the body. This is about vomiting which causes hypovolemia meaning the patient is now going to have more sodium in the cells than water which will mean your patient will be hypernatremic.

[ggmugsy]

That sounds like the same thing to me. WATER is leaving the body during vomiting. The salt in the cells remains. Water doesn't follow sodium. Sodium follows water.

[RNTutor, BSN, RN]

Technically, either could happen. When water follows sodium it is called Osmosis, but when sodium follows water it is called Diffusion...

But because the body has a bunch of semi-permeable membranes that only allow some particles to pass through, usually the statement that "water follows sodium" is more correct. But this is only true when you're talking about fluid and electrolyte shifts in the body, not things like vomiting. With vomiting, it is more that you are At Risk for Fluid Volume Deficit, and of course a fluid volume deficit leads to hypernatremia. But vomiting is not a normal fluid shift anyway.

When it comes to some of the hormones...I think it's interesting. Anti-diuretic hormone (ADH) usually tells the kidneys to retain water. It doesn't tell the kidneys anything about sodium. If you have a pt with SIADH, then they're at risk for hyponatremia, because they are retaining sooo much water, but only retaining the normal amount of sodium. And when the ADH stops coming, as in Diabetes Insipidis (DI), the kidneys lose a lot of water but only lose the normal amount of Na, leading to hypernatremia.

Aldosterone, on the other hand, tells the kidneys to retain sodium. But when they retain sodium, the water naturally follows. That's how Aldosterone regulates fluid volume in the body.

So when thinking about fluid shifts in the body, it is safe to think about it as water follows sodium. Because if the sodium is told to go somewhere, the water generally will go there, too. But if the water is told to go somewhere, the Na continues on its merry way without caring that the water is no longer behind it. But vomiting is a separate concept, and the electrolyte imbalances seen there are going to have to do more with fluid volume deficits.

[Intern67]

Exactly! But the one liner seems to be all that sticks. I noticed this strange trend even before I started Nursing school when I was working as a CNA. I asked an RN a question having something to do with electrolytes and he said, "Let's see....'water follows sodium' so.....um....I don't know."

That was his sum total of knowledge of the subject of water and sodium.

It did not appear to be helpful to him or his patients.