Question about SIADH and Hyponatremia

[melissa0]

Studying for finals and just realized I don't understand this concept...maybe I'm just mixing it around in my head for some reason. But my question is why with SIADH (water intoxication and hyponatremia) you must flush with h20 and NOT saline. If they have hyponatremia why couldn't' you flush with saline... and why would you want to add more water when flushing?

[MunoRN, RN]

I've never heard of that rule. Typically you want to avoid all sources of free water in patients with SAIDH and/or hyponatremia. It is true that with chronic hyponatramia, it's best to raise sodium levels very slowly if at all, which is why hypertonic saline solutions such as 3% saline should be used very carefully and should really only be used to treat symptoms and not to normalize sodium lab levels. That being said, NS (0.9% saline) is isotonic and in an SAIDH patient would cause little if any rise in serum sodium levels, particularly if just used in small amounts as flushes.

[shaas, ASN, RN]

Hi, there.

I am not an expert, but this is what I would deduce from the information given (SIADH accompanies dilutional hyponatremia, so maybe you want to control the water volume now to prevent further dilution, and address Na+ level subsequently, be it via ingestion or what-not so that Na+ level does not increase too quickly):

Could it be because:

1. The Na+ component in saline would further contribute to the problem by retaining more H2O (causes an osmolarity shift if you add more solute).

2. The flushing with H2O does not contribute significantly to increasing the water volume. However, having Na+ bound to H2O molecules would certainly increase it, which leads to further dilution, and worse hyponatremia. Also, because molar ratio is 1:1, as every molecule of Na+ there is water, which means you will not be addressing the Na+ level at all, but increase H2O further.

Just my $0.02.