1/2 ns vs. 0.9% ns

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Specializes in Family Nurse Practitioner.

Why would 1/2 ns be chosen to correct hypotension in a diabetic on lasix over 0.9% ns?

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Specializes in ICU.
Why would 1/2 ns be chosen to correct hypotension in a diabetic on lasix over 0.9% ns?

As in a 500cc fluid bolus? or continuous infusion at say 125cc/hr?

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No idea. If there's a water deficit (also known as hypernatremia), adding more water would be encouraged, and half-normal saline can be considered half water for purposes of electrolyte balance independent of need to replenish intravascular volume (because half-normal saline will replenish intravascular volume a lot less efficiently than NS). Was there a rush to restore intravascular volume? Remember, slow develop, slow repair. See below. Did the patient have hypernatremia, perchance? NS does nothing to change serum sodium.

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. More?

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Specializes in Family Nurse Practitioner.

First 500cc bolus of 0.9%ns and then 1/2ns@50ml/hr. I think 1/2ns has to be slow to prevent cellular edema.

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Specializes in Family Nurse Practitioner.

It makes a lot of sense! Thank you. I'm not sure what his sodium was. The doc ordered labs for the next day. The day before his Na was fine and his SBP was in the 140s the day before and overnight. It dropped to the 80s in the morning. He did seem to be diuresing a great deal..i.e. wetting the chuck..toward the end of the shift the day before and overnight. I mentioned this to doc. Maybe she based her decision on this? As I mentioned before the patient is on lasix. Patient was lethargic which can be sign of hyponatremia. However he was lethargic the day before as well when his Na was normal. I'll be back monday and I'll see how his labs look.

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Specializes in Rehab, LTC, Peds, Hospice.

There's no one ideal fluid for every situation. For resuscitation, crystalloids allow rapid repletion of volume. 0.9% sodium chloride is slightly hypertonic compared to plasma (308 mOsm/L vs 290). Lactated Ringer's is slightly hypotonic (273 vs 290). Since they are both so close to plasma, they are considered the isotonic fluids. You can get a hyperchloremic metabolic acidosis from large volumes of 0.9% NaCl (typically 5+liters). You can get hyponatremic from large volumes of LR. Either are acceptable for volume resuscitation.

For maintenance, sodium content and tonicity matters. I personally think that maintenance fluids for most patients is overutilized. If you use 0.9% NaCl for an extended amount of time, the plasma sodium content will increase and you may get hypernatremic. To avoid this, solutions like 0.45% or lower are used. If the patient is not eating, and you are concerned about providing calories to prevent protein breakdown, dextrose is added to the fluid. 3 liters of a 5% dextrose solution provides 500 kcal a day enough to be protein sparing. Adding D5 to NS results in a hypertonic solution (560 mOsm/L). If the patient's glucose metabolism is impaired, you could cause cellular dehydration from the hypertonic solution. D5 0.45% NaCl avoid this.

Really consider the consequences of fluids. If they don't need salt or water, chances are they don't need any fluid. NPO isn't an indication (we all sleep at night without IVs going).

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Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

Is the only reason for this patients diuresis lasix? Or is there another metabolic process going on? What else can cause diuresis in a diabetic? That may help you decide why which fluid would be more appropriate.

Table of Commonly Used IV Solutions.doc

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Specializes in Family Nurse Practitioner.

Hyperglycemia can cause the diuresis. Wouldn't give patient D5W for this reason. The blood sugars were ok the day before and in the high 200s for the dinner and bedtime fingersticks the night before. It was fine in the morning (no coverage).

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Specializes in Family Nurse Practitioner.

Hx of patient: COPD on home 02, HTN, Pulmonary HTN (maybe from COPD), R heart failure, DM with peripheral neuropathy, osteopenia, and prostate CA

Assessment: Nasty cough unable to clear secretions, desatting episode day before and started on avelox, No fever (but patient is 91), on 2L o2 via NC, frequent tripoding and pursed lip breathing, lethargic (in and out), when awake oriented x3-4. Poor appetite and oral intake. Fluids encouraged. Incontinent. Toward end of previous shift seemed to be voiding a lot which continued overnight so the night shift nurse put on a texas cath. BP the day and night before 140s/70s. In the morning dropped to high 80s/low 40s. Lasix and lisinopril held. After the bolus of 500cc NSS BP increased to mid 90s/mid 50s and stayed that way throughout shift. Electrolytes the day before were normal. no labs the day of. Blood sugar was normal the morning of.

Still not sure what caused the diuresis. Blood sugars were not that high. If hypotonic fluids were given, it means that there was a hypertonic contraction of fluids, meaning the water loss was greater than salt loss, so fluid was pulled out of cells to ECF to compensate. This dehydrated cells which is why needed hypotonic fluids after isotonic fluid bolus. Still don't know what caused the fluid loss.

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Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

It is impossible to really know without knowing everything about the patient. What you are calling diuresis may not really be diuresis. You talk about encouraging fluids.....a reason for increased urine output. They are on a diuretic which can cause episodic increased urine output. The lethargy could be from a build up of CO2 as you mentioned he had frequent "tripoding and pursed lip breathing" and difficulty breathing....Avelox can potentiate Lasix

Acidosis and alkalosis compensation/non compensation...all are inner connected to the acid/base buffering systems, the kidneys, the secretion of bicarb....etc which can also cause increased urine production in an attempt to stabilize the ph.

But we would need a ton of information to be completely accurate.

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I'd been thinking about this lately and nurseprnRN's post has me thinking...why do we give NS to correct low Na+ instead of a hypertonic solution? Sorry, but like many nursing students F&E was not a strong point for me in school. I know that hypertonic is rarely used (never seen it in my practice) but if you want to increase Na+ why not use hypertonic in a small amount/volume/rate?

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