syndrome of inappropriate antidiuretic hormone secretion (SIADH), an abnormal condition characterized by the excessive release of antidiuretic hormone (ADH), which alters the body’s fluid and electrolytic balances. It results in various malfunctions, such as the inability to produce and secrete dilute urine, water retention, increased extracellular fluid volume, and hyponatremia. SIADH develops in association with diseases that affect the osmoreceptors of the hypothalamus. Oat cell carcinoma of the lung is the most common cause, affecting about 80% of involved patients. Other causes are disorders that affect the central nervous system, such as brain tumors and lupus erythematosus; pulmonary diseases, such as pneumonia; cancers of the pancreas and the prostate; and pathological reactions to various drugs, such as chlorpropamide, vincristine sulfate, carbamazepine, and clofibrate. Prognosis depends on the underlying disease, promptness of diagnosis and treatment, and the response to treatment. ▪ OBSERVATIONS: Common signs and symptoms of SIADH are weight gain despite anorexia, vomiting, nausea, muscle weakness, and irritability. In some patients, SIADH may produce coma and convulsions. Most of the free water associated with this syndrome is intracellular, and associated edema is rare unless excess water volume exceeds 4 mOsm. Confirming diagnosis is based on urine osmolality that exceeds 150 mOsm/kg of water and serum osmolality of less than 280 mOsm/kg of water. Normal urine osmolality is 1.5 times serum osmolality. Other significant results include less-than-normal concentrations of blood urea nitrogen, serum creatinine, and albumin and a concentration of sodium in the urine higher than normal. ▪ INTERVENTIONS: Treatment of SIADH commonly includes restriction of water intake and may require administration of normal saline solution to raise the serum sodium level if water intoxication is severe. Furosemide may be administered to block circulatory overload, and drugs, such as demeclocycline hydrochloride and lithium, may be administered to block renal response to ADH. Surgery and chemotherapy are other alternatives to remove or destroy neoplasms that may be the underlying causes of this syndrome. ▪ PATIENT CARE CONSIDERATIONS: The SIADH patient is monitored for any signs of hyponatremia, weight change, and fluid imbalance. The patient is carefully advised on the importance of restricted water intake to prevent water intoxication and is closely observed for any indications of restlessness, congestive heart failure, and convulsions.
