TOPIC DISCUSSION: Hypokalemia causing Hyponatremia

A recent ACID BASE TEACHING CASE in AJKD April 2010 Issue reveals a very important but forgotten concept of severe hypokalemia and how that might lead to hyponatremia and correction becoming a problem.
I urge all to read this case. Its an important lesson for all of us. I was shocked when I read this case and learned a lot from it.

Things to take home:
1. Hypokalemia is an independent predictor for the development of hyponatremia.  The role of K might be less obvious to us. But here is the possible role.  The serum Na concentration is a function of exchangeable Na, K and total  body water.  The mechanism is that when there is K depletion, there is movement of Na into the intracellular compartment with an exchange for K out of the cell. So, when you start repleting the K aggressively, the Na will come out to the cell and start increasing your Na concentration as well.
2. Because of the above concept, the serum Na levels can rise without NaCL administration in an hyponatremic patient when oral or IV potassium repletion is being done.
3. Thiazide induced hyponatremia is often associated with hypokalemia and sometimes severe.
4. Correction of this hypokaleima can be predicted and should be taken into account when you want to correct the Na.
5. You can use the equation exchangable Na + K = serum Na concentration * TBW. Once you have that, you can figure out based on where you want to correct till to see how much K and Na to give to make sure we don't over correct.
6. Even with all these calculations and so forth, sometimes, the urine output is not predictable and there is where trouble can happen as Free water loss is not always exact and depends on the patient's solute intake prior as well.
7. For those reasons, frequent checks of Na and K would help and if you notice quicker rises, Put on the BRAKES to this rise in Na. This can be done using desmopression 1-2ug SQ or IV or using D5W infusion much early on. These both measures will ensure your correction to not happen to rapid.

http://www.ncbi.nlm.nih.gov/pubmed/13163172