How bolus infusions of NaCl may affect low sodium levels...?

Nurses General Nursing

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So, the other day in clinical I had an elderly patient who had low sodium levels and low blood pressure. They gave the pt two bolus infusions of NaCl to help get his/her bp back up, and afterward my instructor asked me a few questions about the effects of giving boluses of NS NaCl to someone who already has low sodium levels. The instructor said that giving those boluses would dilute the sodium levels in the pt even further, causing his/her [Na+] ratios to drop. For some reason, I'm having a really hard time believing that. My reasoning:

1) NS NaCl concentrations are based on regular sodium levels. So, if you have a pt who has lower-than-normal sodium in his/her system, then the NS solutions are hypertonic to the pt's Na+ solutes, and that should cause there to be an increase in [Na+] ratio levels, right?

2) Also, even if the pt's Na+ levels were average, shouldn't the 0.9% NaCl solution not dilute the sodium in the pt's system?

I'm just having issues with this because to me it does not logically follow. What do you all say? Am I mistaken or is my instructor?

Not an appreciable difference. Again, remember that the underlying disease process is still occurring, which means continued fluid retention.

Yes if the patient is hypervolemic due to CHF, liver dz, etc. But there isn't a deficit in TBS in these cases, just increased water retention due to the RAS activation (dilutional hyponatremia). In this case, as I said, fluid therapy must be combined with loop diuretics.

Hyponatremia with hypovolemia (excessive losses via diarrhea, vomting, etc.) causes a decrease in TBW and sodium. You must correct the TBW deficit as well as the sodium deficit.

The OP stated that it was hypervolemic.

given that it was acute hypervolemic hyponatremia (which is what it was) you're agreeing with what i was saying then? NS shouldn't dilute the na+ levels even more?

Also, if this'll help to guide anyone's answer, the pt had a GFR calculation that was only in the low 50s.

It isn't as easy as hyponatremia = treatment X.

It depends on the patient's intravascular volume and underlying cause of the hyponatremia.

If the patient had acute hypovolemic hyponatremia (you mentioned a low BP, which I assume is not a baseline BP), then isotonic saline infusion would be appropriate to treat both issues.

The OP was referencing this comment when they said that. I guess I just read the OP comment as hyPOvolemic.

OP-

Just to clarify, was the patient hypervolemic or hypovolemic?

The OP was referencing this comment when they said that. I guess I just read the OP comment as hyPOvolemic.

OP-

Just to clarify, was the patient hypervolemic or hypovolemic?

Woops. That entire time I was thinking hypo. The member to whom I responded said hypo, I was thinking hypo, have been thinking hypo this entire time, but for some reason I wrote hyper. Sorry :o. If I could go back and edit it, I would.

Does my confusion to my instructor's reasoning make more sense now, stargazer?

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.
Woops. That entire time I was thinking hypo. The member to whom I responded said hypo, I was thinking hypo, have been thinking hypo this entire time, but for some reason I wrote hyper. Sorry :o. If I could go back and edit it, I would.

Does my confusion to my instructor's reasoning make more sense now, stargazer?

You have gotten very good information and without knowing all details about the patient you instructor still maybe correct....

Great thread!

Not to derail the thread, but here's a link to CPM and "Locked in Syndrome." It results most commonly from raising NA+ too rapidly in patients with chronic hyponatremia.

Locked in Syndrome will leave you with your cognition intact, but completely paralyzed except for the ability to blink your eyes, and may be permanent. Frightening.

http://en.wikipedia.org/wiki/Central_pontine_myelinolysis

Can also result from head injury....first job at a LTC had a 21 y/o w/LIS. SAD.

Woops. That entire time I was thinking hypo. The member to whom I responded said hypo, I was thinking hypo, have been thinking hypo this entire time, but for some reason I wrote hyper. Sorry :o. If I could go back and edit it, I would.

Does my confusion to my instructor's reasoning make more sense now, stargazer?

In that case, see post #24.

Not an appreciable difference. Again, remember that the underlying disease process is still occurring, which means continued fluid retention.

Yes if the patient is hypervolemic due to CHF, liver dz, etc. But there isn't a deficit in TBS in these cases, just increased water retention due to the RAS activation (dilutional hyponatremia). In this case, as I said, fluid therapy must be combined with loop diuretics.

Hyponatremia with hypovolemia (excessive losses via diarrhea, vomting, etc.) causes a decrease in TBW and sodium. You must correct the TBW deficit as well as the sodium deficit.

I don't disagree with you. I'm simply attempting to explain how 0.9% NSS bolus infusions could worsen hyponatremia, with the information that was given by the OP.

Specializes in Med/Surg, DSU, Ortho, Onc, Psych.

Was the patient fluid overloaded to start with? Or was he dehydrated due to lack of water?

I remember my instructor ages ago asking us to research this. Hope I get this right from memory!

Water and sodium will always balance in the body, so if the patient received boluses, I can see what your instructor is getting at. She is right saying that the sodium levels will initially drop, but the patient needs fluids to boost his BP and doctors always use NS (where I am anyway) as a first choice for this. Once the fluid has run thru and BP has risen, the sodium and fluid will balance out naturally, therefore making the patient haemodynamically stable (barring other medical conditions).

At least that's what I remember reading!

Specializes in pcu/stepdown/telemetry.

we don't know the history of the pt but a sodium of 131 is not that low and not going to change much after NS bolus. initially may go down but the real problem here is the hypotension which has to be corrected. then if the sodium is lowered less than acceptable they can address by fluid restriction (800-1000cc/day) and some lasix after pressure is stable

* 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, 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

@ GrnTea

I started reading that, but, what on Earth? Saline isn't water and salt? What is it then, just water? Ummmm...no. I'm sorry to be so blunt, but you are the only, and I mean ONLY person I have ever heard say that. I have taken more than just the baseline Chemistry course that's required for nursing, and I have taken them from people who have their PhDs in Chemistry. They have ALL said that saline is sodium chloride in water, and that NaCl is a salt. I have taken more than just the baseline Chemistry course that's required for nursing and have done well in those classes. I KNOW that saline is Na+, Cl-, and H2O, and that NaCl is a salt. I have taken nursing courses in which the professors have MSNs and MBAs and the likes, they have ALL said that normal saline is NaCl and water.

NaCl is a salt. It simply is. I am looking in my old Indiana University-Bloomington Chemistry book right now. It defines salt as "an ionic compound whose cation comes from a base and whose anion comes from an acid" (Jurs et al., 2005). A lot of times you get that NaCl combination from NaOH and HCl. "If the water were evaporated, the solid salt would remain. In the case of HCl plus NaOH, the salt is sodium chloride" (Jurs et al., p. 176, 2005). NaCl is a salt. On page 733 of this book, it has a picture of a "0.9% Sodium Chloride Injection USP" bag with this caption under it: "Sterile saline solution. Saline solutions like this one are routinely given to patients who have lost body fluids" (Jurs et al., 2005).

So, unless you're getting at something that you didn't explain very well in the following 2 paragraphs of your response, I'm not even looking at the rest of what you had to say. Sorry. But, the one, very basic piece of information you've seemingly misinterpreted does not give me confidence to trust in the rest of what you're saying at. all.

Jurs, P. C., Moore, J. W., & Stanitski, C. L. (2006). Chemistry: The molecular

science. (2nd ed.). Belmont, CA: Brooks/Cole--Thomson Learning.

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