Lasix and Hyponatremia

mindlor · Jun 8, 2012

I had a patient who's morning labs came back with K 5.0 and Na 127. The patient had been getting D5 1/2 NS all night at 125 cc/hr and urine output was about 30-40 cc/hr. I was concerned for fluid overload and suspected the fluids might've been responsible for the low sodium as well. The resident rounding wrote for lasix 40 mg IVP as well as fluids to be changed to D5 NS at 75 cc/hr. I thought it was okay at first, but now that I'm home I can't stop wondering what that might do to his sodium. I can't find any concrete numbers on how strong of an effect lasix has on sodium. Any thoughts, resources, ideas?

Need more info. What were the pts vitals? How is Kidney function. The UO that you mentioned is minimally normal......

Why were the on D5 1/2 NS? This is hypertonic and will add volume to the intravascualr space. The pt is more than likely hyponatremic d/t too much fluid on board causing dilution of the electrolytes in the serum.

Changing the client to isotonic fluid and hitting them with a bolus of lasix seems spot on to me, IF the kidenys are functional.

Lasix pulls off water and potassium yes? Potassium and sodium have an inverse relationship. if potassium goes down sodium will typically go up. So, yes, these orders will address the hyponatremia......

MN-Nurse, ASN, RN · Jun 8, 2012

I had a patient who's morning labs came back with K 5.0 and Na 127. The patient had been getting D5 1/2 NS all night at 125 cc/hr and urine output was about 30-40 cc/hr. I was concerned for fluid overload and suspected the fluids might've been responsible for the low sodium as well. The resident rounding wrote for lasix 40 mg IVP as well as fluids to be changed to D5 NS at 75 cc/hr. I thought it was okay at first, but now that I'm home I can't stop wondering what that might do to his sodium. I can't find any concrete numbers on how strong of an effect lasix has on sodium. Any thoughts, resources, ideas?

You can't find any concrete numbers because it depends on a lot of factors. The patient in question has some sort of renal failure, which is probably the cause of the low sodium. In any case, the lasix and IV fluids regimen you describe is very common and will help keep the Na level up as the patient (hopefully) diureses.

You're watching a lot of things on this patient. I/O, BP, heart sounds, BMP labs, lung sounds, mental status....basically everything!

Looking up the types of renal failure and treatments in your med/surg book would be helpful.

CyclicalEvents · Jun 8, 2012

As far as I know he had no renal problems, Cr was normal, I don't remember what his BUN was. Vital signs were stable, pressures 130s-140s.

As for the fluids, I have no idea, I got a very confusing report. He was post op day 1 for a cancerous mass removal of his lung. His original orders were for D5 1/2 + 20K @ 75/hr. Then there was an order to increase to 125/hr. Then another order to continue with just D5 1/2 NS. The nurse told me it was switched because his K was above 5.

My concern I guess was the dose of Lasix with that level of sodium. I'm a new grad nurse in the ICU and this seemed like a very new resident. I overheard her speaking to the attending on the phone and she basically said this patient was doing great. She had not mentioned anything about fluid overload or other concerns I had about this patient overnight. I approached her with my concerns and suggested changing the IVF and giving lasix and she initially ordered 10 mg lasix and I off hand said that seemed like a low dose and that I've seen 40 mg IVP pretty often. She seemed unsure for a second and then wrote an order for 40. I know that it pulls potassium so I was fine with the dose at first, but I figured some amount of sodium would be pulled off as well which might lead to worse things than a bit of fluid overload. I was trying to advocate for my patient, but I overstepped my boundaries with the dosage suggestion. I've done a bit of research and UpToDate seems to be suggesting that he'll probably be okay, but as a new nurse I still have nightmares about all the mistakes I may or may not have made after a shift.

classicdame, MSN, EdD · Jun 8, 2012

i am curious too why the D5 is essential, versus an isotonic fluid.

mindlor · Jun 8, 2012

I too am a brand new nurse. One other bit of friendly advice I will give, is leave your patients at the hospital and enjoy your time off :) You do not have to carry the weight of the world on your shoulders. When you give report to the nurse relieving you, thats it, your responsibility has ended......

UO of only 30-40 mls per hour is borderline though.....

CyclicalEvents · Jun 8, 2012

I too am a brand new nurse. One other bit of friendly advice I will give, is leave your patients at the hospital and enjoy your time off :) You do not have to carry the weight of the world on your shoulders. When you give report to the nurse relieving you, thats it, your responsibility has ended......
UO of only 30-40 mls per hour is borderline though.....

Hah! The resource nurse already told me I need to get a life and quit worrying about work so much. I'm not quite at the point where I can accept that I've done the best I can and enjoy my time off...

Anna Flaxis, BSN, RN · Jun 8, 2012

Assuming that the hyponatremia is caused by excess fluid, then diuresing while simultaneously infusing D5 NS at 75mL/hr sounds appropriate to me. Some sodium will be lost due to the diuresis, but the concentration of serum sodium will increase as excess fluid is excreted, plus you have the NS infusing as well, so you should see the serum sodium balance out. Even though D5 NS is hypertonic, the patient will metabolize the dextrose, and probably needs the calories to help heal postop.

nurseprnRN, BSN, RN · Jun 8, 2012

"why were the on d5 1/2 ns? this is hypertonic and will add volume to the intravascualr space. the pt is more than likely hyponatremic d/t too much fluid on board causing dilution of the electrolytes in the serum."

exactly backwards. half-normal saline is hypotonic. (normal saline is isotonic, more nacl than 0.9% ns is hypertonic.)

the dextrose is gone, used by the cells, in no time, leaving behind the water that carried it. hypotonic solutions go partly into cells and do not increase the volume in the vascular space.

serum sodium tells you about water balance, not sodium. i know this is confusing, so let me try to help with this. i know this is long.

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.

(now, don't overthink this. of course if you want to make a bottle of saline, you will mix plain water with sodium chloride. but read this without thinking about that, because .... well, it works better if you think of saline as an entity for purposes of this discussion. read it and then ask me if you still have questions.)

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?

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 (hematocrit, 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

Anna Flaxis, BSN, RN · Jun 8, 2012

Just wanted to add that even though there is some sodium loss with the Lasix, the patient is losing more water in proportion, which will increase the serum sodium concentration.

nurseprnRN, BSN, RN · Jun 8, 2012

stargazer, that's right. thanks for that clarification.

Anna Flaxis, BSN, RN · Jun 8, 2012

GrnTea,

Am I correct in my understanding that dextrose containing fluids such as D5 NS are hypertonic in the bag, but once in the body, become isotonic, because the body metabolizes the dextrose, just leaving the NS, which is isotonic?