Question: why are you euvolemic in siadh?
Answer: Syndrome of Inappropriate Antidiuretic Hormone (SIADH): a major cause of euvolemic hyponatremia. Euvolemic hyponatremia is characterized by normal or excess extracellular fluid volume. Hyponatremia in SIADH is marked by water retention secondary to an increase in serum vasopressin and urinary sodium excretion.