Patient comes to the ER. She has a a sodium of 119.
Four days earlier the sodium was 134.
ER provides normal saline and the sodium falls to 114.
This is classic SIADH. If you see the serum sodium fall with normal saline, SIADH is your diagnosis.
The fellow ordered all the right tests:
- Urine Sodium: 81
- Urine Potassium: 87
- Urine osmolality: 583
- Uric acid: 2.6
- BUN: 13
- Cr: 0.95
She had negative free water clearance, and a lot of it. For every liter of urine she made it was like she had a 400 mL glass of water.
The patient was on doxepin for mastocytosis. Doxepin is a known cause of SIADH. She also took anti-histamines which cause dry mouth so she was always thirsty. Cruel disease.
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| From the drug insert |
That was stopped and the patient was put on a fluid restriction. She almost immediately turned around and his sodium started to rise. By the following morning the SIADH had completely resolved. Without the inappropriate ADH the pituitary looked at the serum osmolality of 250 and shut down all ADH secretion. This turns the urine to almost pure water. Here are her urine electrolytes from the following morning:
- Urine Sodium: less than 10
- Urine Potassium: 10
- Urine Osmolality: 111
Her electrolyte free water was 87% of urine output.
If you need refresher, here is a video, different numbers but the concept hold.
Sodium rose to 120 the next morning. The patient was making 250 mL per hour of 87% free water. We were concerned about over correction and decided to start D5W at 100 mL per hour to slow the rate of correction. Her sodium rose at a measured pace after that. We planned on adding DDAVP if the sodium went up to fast. Not needed.
Blogged with patient permission. Release on file at PBFluids world headquarters.