SIADH or Syndrome of inappropriate ADH (AVP)

• There is excessive secretion of AVP resulting in pas­sage of decreased volume of highly concentrated urine.
• There is water retention and decrease in plasma so­dium and plasma osmolarity.
• It is called dilutional hyponatraemia.
• It may be asymptomatic or there may be headache, confusion, anorexia, nausea, vomiting, coma and con­vulsions, death.

Causes of SIADH are:

• · Head injury
• · Neoplasms
• · Infections of lungs
• · Abscess
• · Encephalitis
• · Tuberculosis
• · Cerebrovascular accidents
• · Multiple sclerosis
• · GB syndrome
• · Vasopressin
• · Oxytocin
• · Phenothiazines
• · Carbamazepines.

Treatment of SIADH

• Restriction of fluid intake to less than the loss through urine and insensible losses (sweat etc).
• The water intake from food is about 500 ml/day. Insens.ible loss is usually 500 ml/day.
• Liquid intake should be 500 mlless than the uri­nary output.
• IV infusion of hypertonic or 3% saline is given for rapid relief of symptoms.
• Very rapid correction of hyponatraemia should not be done as it can cause myelinolysis charac­terized by quadriparesis and ataxia.
• Demeclocycline (150–300 mg tidY.
• Fludrocortisone (0.05-0.2 mg orally bd).