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

sserrn, BSN · Dec 4, 2011

It def depends on HOW LOW the pt.'s Na+ is, but usu. NS is enough to raise [Na+] to a normal level.

Anna Flaxis, BSN, RN · Dec 4, 2011

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?

If the cause of the hyponatremia is hypervolemic hypotonic, think about what's going on. The person does not have a deficiency of sodium, but rather, has an excess of water. The hyponatremia is dilutional. What happens is that as water and solutes shift out of the intravascular compartment and into the intracellular and interstitial compartments, the decreased circulating volume triggers a release of ADH, resulting in water retention.

0.9% NS is isotonic to normal plasma, but I don't think the osmotic difference between 0.9% NS and hyponatremic plasma is appreciable enough to make all that much of a difference. If anything, there might be a mild osmotic pull, drawing extra water out of the cells (remember, where solutes are, water wants to go), but unless the underlying cause of the hyponatremia is addressed, this would be temporary.

I agree with your instructor that there is likely to be a further decrease in serum sodium levels in this instance, because remember, 0.9% NS is sodium in water. The person already has excess water, and now you are adding more. The concentration of sodium in relation to the water is not enough to raise serum sodium levels appreciably.

I could be way off base, but I'm just thinking out loud here. I think your instructor is probably 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?

In the absence of any pathologies, you are correct, infusing isotonic fluids would not cause a dilutional hyponatremia.

Xsited2baNurse · Dec 4, 2011

I. am. loving. all this information you all are throwing my way. Thank you all so much! From the sounds of all of it, though, it seems as though my instructor may have fed me some misinformation. What I'm gathering is that the [Na+] ratios shouldn't decrease with a bolus IV infusion of NS. They should increase, as I thought that they would. Glad that I didn't go around repeating that to a whole bunch of people.

Also, the sodium level was only mildly low (about 4-5 points below the normal range). So, it was still in the 130s.

Anna Flaxis, BSN, RN · Dec 4, 2011

I. am. loving. all this information you all are throwing my way. Thank you all so much! From the sounds of all of it, though, it seems as though my instructor may have fed me some misinformation. What I'm gathering is that the [Na+] ratios shouldn't decrease with a bolus IV infusion of NS. They should increase, as I thought that they would. Glad that I didn't go around repeating that to a whole bunch of people.

I think it is highly situational, and you can't make blanket statements. The etiology needs to be considered. I would ask your instructor to explain their thinking.

Xsited2baNurse · Dec 4, 2011

if the cause of the hyponatremia is hypervolemic hypotonic, think about what's going on. the person does not have a deficiency of sodium, but rather, has an excess of water. the hyponatremia is dilutional. what happens is that as water and solutes shift out of the intravascular compartment and into the intracellular and interstitial compartments, the decreased circulating volume triggers a release of adh, resulting in water retention.
0.9% ns is isotonic to normal plasma, but i don't think the osmotic difference between 0.9% ns and hyponatremic plasma is appreciable enough to make all that much of a difference. if anything, there might be a mild osmotic pull, drawing extra water out of the cells (remember, where solutes are, water wants to go), but unless the underlying cause of the hyponatremia is addressed, this would be temporary.
i agree with your instructor that there is likely to be a further decrease in serum sodium levels in this instance, because remember, 0.9% ns is sodium in water. the person already has excess water, and now you are adding more. the concentration of sodium in relation to the water is not enough to raise serum sodium levels appreciably.
i could be way off base, but i'm just thinking out loud here. i think your instructor is probably right.
in the absence of any pathologies, you are correct, infusing isotonic fluids would not cause a dilutional hyponatremia.

well, going off what you're saying, i feel as though after the introduction of the ns into the ecf, the volume of ic h2o that would be leaving the cells would only be enough to reestablish the na+ ratios that were present before the iv bolus. i say that because the level of the pt's extracellular na+ before the iv push was (i'm assuming) at a a level that would induce dynamic equilibrium between the icf and ecf. the extra sodium introduced via the ns solution would only pull out enough water from the cells to reach a dynamic equilibrium between it and the cells, right? (it's only going to be the amount of water needed to equalize the new na+). so, the ratios should actually still be the same, shouldn't they be? you'll have the water present that was there to begin with to equalize the osmotic pressure of the original na+, plus some extra water to help equalize the osmotic pressure of the newly introduced ns. right?

Xsited2baNurse · Dec 4, 2011

I think it is highly situational, and you can't make blanket statements. The etiology needs to be considered. I would ask your instructor to explain their thinking.

Hmmm...probably so. Although, her exact words were "even though there's 0.9% NaCl in the solution, it's enough fluid to dilute the original Na+ even more." I thought that she was specifically blaming the dilution of the serum Na+ on the NS and just the NS. Idk. I'll make sure to ask her the next time I see her...because I'm confused. I've gained a lot of knowledge from you guys in the course of my confusion, but still...confused. lol.

PetERNurse · Dec 4, 2011

There are a few different types of hyponatremia:

1- Hyponatremia w normal plasma osmolality (aka "pseudohyponatremia"). Usually due to hyperlipidemia/hyperproteinemia, which interferes with sodium measurement giving a falsely low sodium reading.

2- Hyponatremia with increased plasma osmolality. Usually due to hyperglycemia, though other impermeant solutes can cause this as well (mannitol, etc.). This causes a shift of fluid from the ICF space into the IV space. Correcting the underlying cause usually corrects the hyponatremia as the fluid is allowed to move back into the cells.

3- Hyponatremia with decreased plasma osmolality ("true" hyponatremia). This occurs when there is a true decrease in total body sodium. The sodium deficit must be calculated and administered over the appropriate time period. If there is 3rd spacing taking place, hypertonic saline may be required, otherwise IVF therapy is based on raising the sodium at the appropriate rate.

Administering NS to the patient will not drop the P TBS (unless there is renal dysfunction). Not sure what your instructor was thinking. Fluid will shift, which is what we want. Like you eluded to, we are looking for apporpriate homeostasis.

If the patient is hyponatremic, fluid therapy is indicated. Depending on the severity and how quickly the derangement formed will depend on how much sodium to administer how quickly (usually do not want to raise serum sodium faster than 0.5-1 meq/L/hr).

If the patient is hypotensive due to hypovolemia, then NS is indicated to replace IV volume.

In hypervolemic patients with hyponatremia loop diuretics should be considered along with NS.

You mentioned the patient is elderly and hypotensive? CHF (if applicable here) with hyponatremia provides a poor prognosis... :uhoh3:

Anna Flaxis, BSN, RN · Dec 4, 2011

Hmmm...probably so. Although, her exact words were "even though there's 0.9% NaCl in the solution, it's enough fluid to dilute the original Na+ even more." I thought that she was specifically blaming the dilution of the serum Na+ on the NS and just the NS. Idk. I'll make sure to ask her the next time I see her...because I'm confused. I've gained a lot of knowledge from you guys in the course of my confusion, but still...confused. lol.

It sounds like what she meant was that even though there is sodium in the solution, there is enough water in the solution to dilute serum sodium levels even further.

PetERNurse · Dec 4, 2011

It sounds like what she meant was that even though there is sodium in the solution, there is enough water in the solution to dilute serum sodium levels even further.

I'm not sure that is physically possible. If you are adding a solution that has 154 meq/L Na to a solution that is 130 meq/L Na, it will raise the sodium content of the final product (above 130 meq/L). There may be initial fluid shift due to homeostatic mechanisms, but the TBS will go up not down.

Xsited2baNurse · Dec 4, 2011

It sounds like what she meant was that even though there is sodium in the solution, there is enough water in the solution to dilute serum sodium levels even further.

Yeah, which is where I got confused...because given that the pt's sodium concentration levels [should've been] lower than the 0.9 percent NaCl, that doesn't make sense. The water pulled out from the cells to help compensate for the slightly hypertonic solution introduced to the system should've at most only taken the [Na+] back down to what they were before the infusion. It's just weird and doesn't make sense; and I do need to ask her. But, just judging from how often she changes what she tells people when it comes to things like that, I'm worried that she's just going to end up saying the exact opposite next time I ask her. "Umm, no, what're you talking about? Her sodium levels are going to increase, and her [Na+] will stay the same, if not increase slightly. duhhhhhh:uhoh3:" .... :lol2:

leslie :-D · Dec 4, 2011

great info here.

Hyponatremia Clinical Presentation

http://emedicine.medscape.com/article/242166-clinical#showall

leslie

Anna Flaxis, BSN, RN · Dec 4, 2011

It sounds like what she meant was that even though there is sodium in the solution, there is enough water in the solution to dilute serum sodium levels even further.

I'm not sure that is physically possible. If you are adding a solution that has 154 meq/L Na to a solution that is 130 meq/L Na, it will raise the sodium content of the final product (above 130 meq/L). There may be initial fluid shift due to homeostatic mechanisms, but the TBS will go up not down.

Not appreciably.

For instance, take a 200lb. man. He weighs about 91kg. If 60% of his weight is total body water, then that's 55 liters of total body water. Add an extra 10lb. of water weight (he's retaining water r/t CHF, for instance), and you have a total of 59 liters of total body water.

59 x 130 = 7,670

Say you add 154mEq in 1 liter of water.

Your total sodium is now 7,824mEq, and your total body water is now 60 liters.

7,824/60=130.4.

Not an appreciable difference, and again, remember that the underlying disease process is still occurring, which means continued fluid retention, which means continued serum sodium decreases.

My numbers are clearly not exact, since total body sodium is high in relation to serum sodium in cases of edema related to cardiac or renal disease, and my numbers were based upon the serum concentration. Total body sodium would actually be higher than in my calculations, making any increase in sodium even less appreciable than in my example.