Hyponatremia, in it’s simplest definition is low salt levels in the blood. Therefore, it makes sense if something is low to take more of it to raise the levels. In fact, this is the case for many of the other electrolyte deficiencies. If potassium is low, providers recommend taking potassium and if magnesium is low, we recommend magnesium. So why in the case of Hyponatremia, do we typically not recommend giving more salt?
The easy answer is, “it’s not a salt problem, it’s a water problem.”
It’s a bit more complicated than that, of course. There are instances when giving salt or salty fluid is the correct approach. These cases are the minority however, and are typically seen more acutely or in the hospital setting when someone is truly volume depleted. Patients may notice dehydration is not mentioned as by definition, this typically associates with a lack of water and Hypernatremia. In cases such as volume depletion, there is a story of fluid loss usually through the gut, such as diarrhea, vomiting or urinary losses. Less often we may see volume depletion with sweating or even burns. Often in these circumstances folks are still drinking water but unable to hold down food, so they are exacerbating the low sodium state by further diluting the blood. Providers would check things like urinary sodium (usually low due to the body holding onto salt), urinary concentration (osmolarity, usually high due to the body holding onto water) and will provide both salt and water via a saline infusion. This should correct the problem quickly as once the body gets enough salt and water back it will be able to self correct the low sodium levels with diluted urine.
In contrast to the volume depleted scenario, are the times when sodium is low but patients are volume overloaded. We see this condition most often in those who have congestive heart failure, cirrhosis or heavy protein losses via the urine. In these scenarios the urine studies can appear similar to the volume depleted state (low urine sodium, high urine osmolarity) but the physical examination is quite different.
When your volume depleted your:
- skin turgor is slow to spring back
- your armpits are dry
- your not swollen and may have wrinkles
- your blood pressure is low, especially when standing
- your weight is down
When your volume overloaded, you will see edema, your weight is up, you may be short of breath and your abdomen may feel distended. In this instance, the usual treatments are diuretics like furosemide, coupled with sodium and water restriction. This will help reduce the excess salt and water, and improve the sodium levels. Tolvaptan, a pure aquaretic (pee water only, no salt loss) can also be utilized.
Another scenario we encounter, would be those that have Hyponatremia, but are deemed euvolemic. This is neither volume depleted or volume overloaded. This state manifests with normal or high blood pressures, minimal or no swelling and urine studies depicting a high urine salt level and a concentrated urine. This is most often due to the Syndrome of Inappropriate Anti-Diuretic hormone release (SIADH). Other possibilities of euvolemic Hyponatremia include thyroid, adrenal, primary polydipsia or tea and toast disorders. With SIADH “you are what you eat,” in terms of salt. The more salt consumed the more salt is excreted, this is termed desalination. We see this happening when we administer a bag of Normal Saline, which contains 9 grams of sodium chloride and 1 liter of water. If your urine is more concentrated than the IV drip you will pee out all that salt and hold onto some of the water, diluting your blood sodium further. Salt tablets are a little better, as they are just the salt without the water but you would need tremendous amounts to make a meaningful difference. Take the following example: if your urine was stuck in a concentrated solution of 500 mosm/L, as is often the case in SIADH, it would take nearly 30, 500 mg salt tabs to help the kidneys excrete just 1 liter of water. That’s a whole lot of salt, with risks of dry mouth/tongue, swelling, and elevated blood pressure. Not to mention all the water it would take to swallow all those dry tablets. This is why salt really doesn’t work.
UreaAide, on the other hand, provides enough solute to rid the body of 1 liter in just 2, 15 gram doses. UreaAide contains no salt, and therefore no fear of swelling, elevated blood pressure or dry mouth. UreaAide provides 250 mosm/L of solute, allowing just 1 dose to help the kidneys excrete half a liter of water. This will help raise the sodium effectively by taking the excess water out.
In summary, salt doesn’t work because it’s really not a lack of salt that is the problem in SIADH induced Hyponatremia, but an excess of water, and the inability of the body to excrete the water appropriately.