WHATEVER

SIADH =>diagnosis of exclusion

l          Etiology

1. CNS: SAH, stroke, trauma
2. Pulmonary: SCLC, pneumonia, positive-pressure breathing
3. Drugs: antipsychotic drugs

=>Hypotonic hyponatremia: euvolemia(or mild-hypervolemia)

=>導因於水分過多稀釋血鈉

l          S/S: Low Posm

        High Uosm > 100

        Normal UNa

l          Tx: if asymptomatic=> strict water restriction (eg, 250 to 500 mL/24 h)

   Hypertonic saline (+/- loop diuretic)

       IV rate<12mmol/L/d = 0.5mmol/L/hr 避免 central pontine myelinosis

       (mmol=mEq X 帶電量)

l          Euvolemia之因:

    Total fluid volume組成

       a. ECF

            1) Plasma

            2) Interstitial Fluid

            3) Lymph

       b. ICF

       c. Movement of fluid in one compartment affects the others

Euvolemic hyponatremia: In euvolemic (dilutional) hyponatremia, total body Na and thus ECF volume are normal or near-normal; however, TBW is increased. (water shifted to ICF due to osmolarity balance)

l          Primary polydipsia can cause hyponatremia only when water intake overwhelms the kidneys' ability to excrete water. Because normal kidneys can excrete up to 25 L urine/day, hyponatremia due solely to polydipsia results only from the ingestion of large amounts of water or from defects in renal capacity to excrete free water. Patients affected include those with psychosis or more modest degrees of polydipsia plus renal insufficiency.

More about Hyponatremia(merck manual)