The patient had SIADH due to viral encephalitis. We started tolvaptan 30 mg and his SIDAH rapidly reversed with the sodium rising from 124 to 128 overnight and up to 136 in the following week. Along with his improved sodium the patients mental status improved. I attribute that more to improvement in the encephalitis than the normalized osmolality but the association is there.
I stopped the Tolvaptan after 8 days and the next morning here are his urine chemistries:
Urine sodium 20, urine osmolality was 614. Somehow, I got a urine chloride rather than the urine potassium I ordered. The sodium nudged up to 137 off the tolvaptan. It looks like the SIADH has resolved with the urine sodium falling from 148 prior to the drug to 70 after the first dose to 20 off the drug completely.
Also note that even though the urine osmolality (614) is greater than serum osmolality, the serum sodium can still rise. This is because the electrolyte free water is still positive, despite a negative solute free water.
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