Syndrome of inappropriate antidiuretic hormone release
Syndrome of inappropriate anti-diuretic hormone release (SIADH) is a common cause of hyponatraemia and is a final pathway of many pathologies that produce hyponatraemia. Many patients present with a mixed aetiology so may not meet the following prerequisities. A mistake often made in acute hospital medicine is to label and even manage a patient as SIADH when the most important issue is water intoxication, which would be clear from inspection of a fluid balance chart, recent prostate surgery or even an oral history of recent fluid intake.
- Urine sample
- [Na+] >20 mmol/l
- Urine osmolality > 500 mmol/kg
- Blood test
- [Na+] < 125 mmol/l
- Plasma osmolality < 260 mmol/kg
A common cause and the mechanism of production of hyponatraemia of most drugs, for example anti-depressants and anti-epileptic agents. It must be remembered that drugs such as amiloride, acetazolamide, thiazide diuretics, ACE and Angiotensin-II inhibitors act on the kidney directly to produce hyponatraemia.
- Treat cause
- Water restriction < 1200 mls/day
- Induce Diabetes insipidus using demeclocycline