0.45% NS is Hypernatremia?

[CBsMommy]

So, I am trying to wrap my head around why we would use 1/2 NS in hypernatremia patients.

Here's what I have worked out so far...

1/2 NS is a hypotonic solution which would cause cells in the blood to swell with water.

The only thing that I could think of would be that this would change osmolarity in the blood thus pulling in water from the interstitial fluid to replace blood volume, which would then dilute the serum sodium level. Am I on the right track?

I've googled and can't seem to find an answer on the cellular level, just that we do use 1/2 NS to correct hypernatremia.

Thanks in advance.

[dudette10, MSN, RN]

I think water loss (e.g. diarrhea, d. insipidus, etc.) most commonly causes hypernatremia which then causes water to be pulled from the interstitial spaces, so the 1/2 NS wouldn't correct that in the way you explained. The body wants to rebalance the osmolarity so it's pulling water from the cells and the interstitial spaces to do so, causing dehydration.

I would think 1/2 NS would be used to increase blood volume while diluting the plasma to rebalance the sodium levels. If we used isotonic NS, blood volume would increase, but sodium levels would still be high.

I think.

[CBsMommy]

If we used isotonic, the sodium levels would remain the same.

The second half of your paragraph is what I was eluding to in my statement but how would 1/2 NS increase blood volume if not pulling from the interstitial spaces? But I do see what you're saying about causing dehydration in the tissues. Although, if we have an excess of water in the tissues (edema) and hypernatremia in the blood, then we would have a win/win situation. So, maybe the only time you would use 1/2 NS is when we have edema with hypernatremia?

[CBsMommy]

Intravascular pulls from interstitial which then pulls from intracellular....right?

So if we hyperinflate a cell within the blood, which would change osmotic pressure, more water would then be pulled into the vascular space from the interstitial space (thus diluting the SERUM sodium content). Which would only make sense to do if we had edema within the surrounding tissues, otherwise, you are right, that would cause dehydration in the tissues.

Anybody else, please feel free to chime in. I still think I'm missing the piece of a puzzle somehow.

[Mike R, ADN, BSN, RN]

Here's how I see it. Hypernatremia would mean your vascular system is already hypertonic and probably pulling fluid from cells and 3rd space into the vascular system through oncotic pressure. Giving 0.45%NS as a hypotonic soln. into the hypertonic vascular system would dilute the sodium, decrease oncotic pressure and return fluid out of the vascular system and into cells through osmosis.

Haha but it's purely a guess. I just learned this stuff last week!

[Mike R, ADN, BSN, RN]

So, maybe the only time you would use 1/2 NS is when we have edema with hypernatremia?

The way we were told was this: A hypertonic soln. in the vascular system will pull water from outside the vascular system. So if you have fluid volume overload, (ie: edema) one would want to use a hypertonic soln. (like 3% NACL or D5NS). So by using D5NS in a isotonic vascular system, it will turn hypertonic and you will pull excess fluid from third space into the vascular system and out into the kidneys.

[dudette10, MSN, RN]

If we used isotonic, the sodium levels would remain the same.

What I meant was that if we used isotonic, it wouldn't correct the hypernatremia. The levels would remain high.

The second half of your paragraph is what I was eluding to in my statement but how would 1/2 NS increase blood volume if not pulling from the interstitial spaces?

I'm not sure I'm following you. Why would 1/2 NS pull water from the interstitial spaces? It would, however, increase blood volume because you're putting it directly into the vein.

But I do see what you're saying about causing dehydration in the tissues. Although, if we have an excess of water in the tissues (edema) and hypernatremia in the blood, then we would have a win/win situation. So, maybe the only time you would use 1/2 NS is when we have edema with hypernatremia?

I'm wondering if something else is going on with the patient that is causing edema. I don't think the hypernatremia is causing it; hypernatremia by itself would cause dehydration, not edema.

So, all that is to say, I'm not sure. :)

[dudette10, MSN, RN]

The way we were told was this: A hypertonic soln. in the vascular system will pull water from outside the vascular system. So if you have fluid volume overload, (ie: edema) one would want to use a hypertonic soln. (like 3% NACL or D5NS). So by using D5NS in a isotonic vascular system, it will turn hypertonic and you will pull excess fluid from third space into the vascular system and out into the kidneys.

But, you wouldn't want to use a hypertonic solution in a hypernatremic state, would you? It would make the hypernatremia worse.

[dudette10, MSN, RN]

found it!

"volume overload

volume overload generally refers to expansion of the ecf volume. ecf volume expansion typically occurs in heart failure, nephrotic syndrome, and cirrhosis. renal na retention leads to increased total body na content. this results in varying degrees of volume overload. in heart failure, the increased ecf volume results in decreased effective circulating volume, which in turn causes decreased organ perfusion leading to clinical sequelae. serum na concentration can be high, low, or normal in volume-overloaded patients (despite the increased total body na content).

an increase in total body na is the key pathophysiologic event. it increases osmolality, which triggers compensatory mechanisms that produce water retention. when sufficient fluid accumulates in the ecf (usually > 2.5 l), edema (see approach to the cardiac patient: edema) develops.

among the most common causes of ecf volume overload are the following:

• heart failure
  
• cirrhosis
  
• renal failure
  
• nephrotic syndrome
  
• premenstrual edema
  
• pregnancy
  

clinical features include weight gain and edema. diagnosis is clinical. treatment aims to correct the cause."

http://www.merck.com/mmpe/sec12/ch156/ch156c.html#sec12-ch156-ch156c-689

[Mike R, ADN, BSN, RN]

But, you wouldn't want to use a hypertonic solution in a hypernatremic state, would you? It would make the hypernatremia worse.

You got me. I totally read her statement wrong. You're right! My comment was geared toward edema in general w/o hypernatremia. Don't mind me.

[dudette10, MSN, RN]

You got me. I totally read her statement wrong. You're right! My comment was geared toward edema in general w/o hypernatremia. Don't mind me.

LOL! Hey, I'm as flummoxed as the next person over this edema/hypernatremia bit. When I found that link, it became clearer...something else is going on with the patient than just run-of-the-mill hypernatremia d/t GI losses.

[CBsMommy]

Thanks for your replies. I wasn't trying to deal with fluid volume deficits or excess.

I was just trying to figure out why someone with a high level of blood sodium would get 1/2 NS because in my mind, it wouldn't fix the problem.

I will ask the teacher tomorrow for further clarification and will let you know. Thanks again for going out of your way to help!