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5 out of 8

Not true about SIADH (AIIMS Nov 011)

A VAP tans are class of drugs approved for its treatment

B Water loading test is done to diagnose it

C Serum sodium of 125 mg/dl can be seen

D Euvolemia to hypovolemia may be seen and urine sodium is normal or low

Ans. D

Euvolemia to hypovolemia may be seen urine sodium is normal or low

Clinical features of SIADH

They are due to hyponatremia which are related to osmotic water shift. It lead to increase intra cellular fluid volume in the brain cell causing swelling of the brain cell which lead to cerebral edema. Patient may be asymptomatic, or may have convulsion COMA or death.

Laboratory features of SIADH

1. Hyponatremia (serum sodium < 135 mEq/L)

2. Inappropriately elevated urine osmolality (> 100 mosm/kg)

3. Decreased serum osmolality (< 280 mosm/kg)

4. B.U.N. and serum uric acid tends to fall because of plasma dilution and increased excretion of nitrogenous products.

5. Serum potassium and Bicarbonate levels are normal in SIADH.

6. Increase urinary sodium (More than 30 meq/lil

7. Water loading test is done

Extra Edge: Water loading test

In SIADH there is an abnormal water load test (i.e. inability to excrete at least 90% of a 20 ml/kg water load in 4 h and/or failure to dilute urine osmolality <100 mosm/kg), and there is plasma ADH levels inappropriately elevated relative to plasma osmolality.

Treatment of SIADH:


1. Standard first line therapy is water restriction.

2. If more rapid correction of hyponatremia is desired, the fluid restriction can be supplemented with i. v. infusion of hypertonic saline (3%).

Extra Edge:

A rapid correction will produce central pontine myelinolysis which is an acute potentially fatal neurological syndrome characterized by quadriparesis, ataxia and abnormal extraocular movements.

To prevent this complication the hypertonic saline should be infused slowly.

Chronic SIADH:

Hyponatremia can be corrected by with à a. Demeclocycline b. Conivaptan

Conivaptan & tolvaptan are new drugs. It is a treatment option for hyponatremia in place of Demeclocycline.

(Harrison’s 18th Edition, Pg 349).