Hyponatremia/Hypernatremia

[trudub]

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Anyone know where there is a good tutorial on hyponatremia/hypernatremia? Particularly, I am interested in something that describes the pathophysiology that causes certain conditions to produce say euvolemic hyponatremia versus hypervolemic hyponatremia. Anything?

 

[Rendar5]

after ruling out thyroxine and cortisol deficiences (prevent the ability to dilute water), u've pretty much got SIADH (tumor, drugs, idiopathic, etc.). ANF helps take care of the hypervolemia, so just cause u can't piss out free water, doesn't mean u can't piss.

This is why SIADH only presenting as hyponatremia w/o hypertension always confused me until I understood that there are mechanisms against volume overload. Given enough time, you'll get the overload, but hyponatremic symptoms will appear before this.

As for hypernatremia, gotta check ur aldo and PRA levels, since excess aldosterone causes hypernatremia w/ hypokalemia, and ur ADH levels for DI. Since I'm only in my second year, I don't know if I've covered this stuff completely yet.

Oh, and u gotta see if the person's taking diuretics, remembering what they each do to ur electrollyte levels.

hmm...tutorials for hypernatremia might be useful, though. i'll see what i can find. don't know if there's anything out there.

 

[trudub]

Thanks for your reply Rendar. I am with you with what you said. I am a second year too. We are covering this stuff right now. What I was looking for was something that explains the physiologic problems as reasons why things manifest the way they do. I could definitely use this for both hypernatremia/hyponatremia. I feel like right now I am just memorizing algorithms and thought some physiology with it would be nice.

 

[LAZYGUY]

Anyone know where there is a good tutorial on hyponatremia/hypernatremia? Particularly, I am interested in something that describes the pathophysiology that causes certain conditions to produce say euvolemic hyponatremia versus hypervolemic hyponatremia. Anything?

Hypovolemic hyponatremia: the total body Na is low (accounts for hypovolemia); total body water is also low but the deficiency of total body Na is greater than the deficiency of total body water so that there is more water than sodium in the ECF --> hyponatremia

Hypervolemic hyponatremia: the hypervolemic pathophys is the opposite of the above, the hyponatremia pathophys is the same.

euvolemic hyponatremia: Total body Na is normal so that volume is normal; hyponatremia is caused by excess total body water. (there is no signs of fluid overload b/c the water distributes mostly into the intracellular space)

 

[trudub]

Thanks for that LazyGuy but again, I am looking for something a little more in depth. I could use a link or a reference of some kind that talks about this in detail with physiology to go with it. In addition, it anyone could explain to me how and why BUN:Creatinine ratios are altered in various volume aberrations I would appreciate it.

 

[LAZYGUY]

Thanks for that LazyGuy but again, I am looking for something a little more in depth. I could use a link or a reference of some kind that talks about this in detail with physiology to go with it. In addition, it anyone could explain to me how and why BUN:Creatinine ratios are altered in various volume aberrations I would appreciate it.

have you tried pathophys for the boards/wards, if you haven't its got some good stuff in there. If you are looking for more depth then you might want to pull out guyton's phys and look through the fluid/renal section.

 

[LAZYGUY]

This is why SIADH only presenting as hyponatremia w/o hypertension always confused me until I understood that there are mechanisms against volume overload. Given enough time, you'll get the overload, but hyponatremic symptoms will appear before this.

What I understood about this is that since you are just absorbing alot of water (not solutes) from the collecting tubule you are going to take that into to your interstitium. The majority is going to go into your ICF compartment (2/3) and you won't experience hypertension because of your high capacitance in the veins. If you had solutes in your ECF due to hormones like ALDO pulling in Na+ then you would be pulling fluid out of your ICF and --> hypertension but this is not the case with SIADH.

 

[trudub]

Rendar, do you know how cortisol and thyroxine deficiency prevent you from diluting your urine? Overall, in these conditions you are excreting sodium in excess of water right? So this causes a person to be hypervolemic, hypernatremic?

 

[Rendar5]

Rendar, do you know how cortisol and thyroxine deficiency prevent you from diluting your urine? Overall, in these conditions you are excreting sodium in excess of water right? So this causes a person to be hypervolemic, hypernatremic?

I asked our endocrine professor that actually when it was brought up. And he just didn't really have an answer. He mentioned some things that it could either affect the Thick ascending limb where u're pumping out salt and diluting the luminal fluid. Or it could affect the collecting duct, and would be necessary to maintain the impermeability (no impermeability, it acts as if there's ADH there and the water just drains back into the medulla. I'm looking through my renal pathophys notes now. and should have an actual answer (I hope) in 15 minutes.

 

[Rendar5]

It isn't a hypervolemic condition initially, though. Or at least it doesn't act like it. I'm pretty sure it's cause of Atrial Natriuretic Peptide/Factor (learned two different words in renal and endocrine, which is why i'm confusing myself here).

 

[Rendar5]

hmm...ok, cortisol suppresses secretion of ADH. not enough cortisol, ADH levels are abnormally increased. Also, there is additional salt loss in a more generalized adrenal insufficiency mostly due to aldo I would think (cortisol has an equivalent Na+ retention to aldo, but is degraded by the mineralocorticoid recepters, so doesn't affect it really). And there's also volume depletion in adrenal insufficiency (secondary to the salt loss i assume).

Now as for thyroxine, it seems the endocrine guy was right. We really don't know exactly why hypothyroidism can cause hyponatremia. Just know that it also can cause SIADH symptoms. Which is why standard procedure is to start checking those two hormones before checking for SIADH and its causes.

 

[Rendar5]

This sounds right too. I guess I'm just more in endo mood and want to explain everything with hormones now 🙂 I wouldn't be surprised if ANP has some effect (and it does help cause vasodilation), but yeah, I totally forgot about cellular swelling, which causes the neurological symptoms of hyponatremia.

What I understood about this is that since you are just absorbing alot of water (not solutes) from the collecting tubule you are going to take that into to your interstitium. The majority is going to go into your ICF compartment (2/3) and you won't experience hypertension because of your high capacitance in the veins. If you had solutes in your ECF due to hormones like ALDO pulling in Na+ then you would be pulling fluid out of your ICF and --> hypertension but this is not the case with SIADH.