Saline infusion is useful in most SIADH patients and the increase in plasma sodium is related to urinary osmolality and not to urinary sodium and potassium loss
ASN 30th Annual Meeting, San Antonio
J Am Soc Nephrol (Sep) 8:106A 1997
82 nonedematous hyponatremic patients were treated with 2L isotonic saline over 24h. The plasma sodium concentration increased in most patients. The sum of urinary sodium plus potassium concentration (UNa+K) and urine osmolality (Uosm) predicted plasma sodium increase. Only 3 patients became more hyponatremic with saline infusion. The authors predict that hyponatremia will worsen with saline infusion only in patients with Uosm > 539 mOsm/kg.
Comment: It has been postulated on theoretical grounds that hyponatremia will worsen with isotonic saline infusion in SIADH because the sodium will be excreted in the urine whereas some of the water will be retained due to ADH effect. However, this has never been demonstrated in a clinical study. Indeed, if the urine sodium plus potassium concentration or urine osmolality is relatively low, it might be expected that the serum sodium would increase because electrolyte gain would exceed water gain (i.e., the patient would effectively be receiving hypertonic fluid). The patients in this report were nonedematous. However, it is not clear how this diagnosis of SIADH was made. It can be difficult clinically to differentiate between mild hypovolemia and euvolemia (the former group would be expected to improve with saline). (David J. Leehey, M.D., Loyola University at Chicago)
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ASN 30th Annual Meeting, San Antonio
Sodium/water transport : Hyponatremia