SIADH

ü  ADHà 腎的V2à distal tubule and collecting ductàfree water retention and dilutional hyponatremiaà elevated urine osmolality in the setting of a low plasma osmolality

※ Essential diagnostic criteria:

ü  Plasma osmolality <275 mOsm/kg

ü  Urine osmolality >100 mOsm/kg and urine Na >20 to 40mEq/L

ü  Euvolemia

ü  Normal renal, adrenal, and thyroid function tests

ü  No recent use of diuretic agents

※ Euvolemic hypotonic hyponatremia:

ü  The most common cause of euvolemic hypotonic hyponatremia is SIADH.

ü  Characterized by low to normal total body sodium and normal to elevated total body water.

²  Hypothyroidismà dysregulation of ADH release or clearance, effects on vascular tone, cardiac output, and renal blood flow

²  Adrenal insufficiencyà caused by the loss of negative feedback on ADH secretion

²  Primary polydipsia

²  Potomania

²  Thiazide diuretics

²  Reset osmostat syndromeà shift in the set-point for ADH

²  Nephrogenic syndrome of inappropriate antidiuresisà mutations in the renal vasopressin V2 receptor causing increased water resorption，表現同SIADH但ADH測不到

ü  SIADH is usually self-limited, and the primary management strategy is to correct the underlying etiology.

ü  Loop diureticsà增加free water 排出、讓腎對ADH反應下降àenhance the effect of solute loading

ü  Demeclocycline acts on the renal collecting tubules to diminish responsiveness to ADH. The major side effect is nephrotoxicity.

ü  Vasopressin receptor antagonists exert their activity on renal V2 receptors resulting in a selective water diuresis without affecting sodium excretion