Lithium and Dehydration

[BraveHeartABC]

Can somebody explain this to me like I'm 5. I don't understand how dehydration can cause Lithium toxicity. Let's say a healthy individual is dehydrated for the sake of simply not drinking enough fluids-no diarrhea, no vomiting. Wouldn't this individual have hypernatremia? Which is confusing to me because hyponatremia causes lithium toxicity. So I would think that this person would have a less therapeutic lithium level with the elevated sodium, not toxicity level.

[TriciaJ, RN]

I'm not sure but I think it might have something to do with the narrow therapeutic window. I think fluid/sodium levels have to be fairly balanced, which is why regular blood work is required.

Another complication is that lithium is known to cause diabetes insipidus in some people.

[Tegridy]

Concentrated drug levels and reduced renal clearance from not drinking enough. In addition to the above.

[Sam. W, MSN, APRN]

if you are dehydrated, the lithium would build up in your blood, right?

[Tegridy]

It’ll just be more concentrated. The sodium part has something to do with like low sodium causing more of the lithium to stay inside cells. Through some weird ion channel that isn’t one of the common ones

[Grande_latte04]

This is interesting. I never really thought about this super critically. I looked it up and lithium inhibits the function of voltage gated sodium channels in adrenal chromaffin cells. If those channels can not become activated Na+ can not be released from the cells (I guess reiterating what someone said above) and then cathecholamines but also would prevent blood sodium levels from rising (I guess.. that's how it works)

[RatchedAfterMidnight, MSN, APRN]

Everyone is on track! You can have a dehydration with hyponatremia or hypernatremia. Lithium is an element in the same group of the periodic table as sodium. Sodium is involved in so many processes in the body that to this day we continue to not know exactly how Lithium helps with mood and behavior...we give it because "it just works." Lithium accumulates in the collecting tubules and interferes with ADH's ability to increase water permeability. With long term use of lithium this decreases the kidney's ability to concentrate urine. If this person was not drinking enough water as the cause for dehydration, it is "extra renal" -a non kidney- cause of the dehydration. We have to get in there, assess the patient, and do the lab work to find out the cause. If it's from decreased drinking, the patient could present with euvolemic hypernatremia. If the patient has N/V/D or chronic bleeding somewhere it could be hypovolemic hypo or hypernatremia. Check out this guideline, I think you would find it helpful:

https://www.aafp.org/afp/2015/0301/p299.html

If the patient isn't drinking enough water, the lithium toxicity is mild, I would hold the lithium, observe them, and the treatment would be oral rehydration/IV fluids if unable to tolerate oral.