A patient has developed syndrome of inappropriate antidiuretic hormone (SIADH) after suffering a traumatic brain injury. After treatment has been initiated, the nurse assesses the patient for signs of improvement, including

decreased urine osmolality
increased serum sodium
increased urine output

Explanation

• The syndrome of inappropriate (secretion of) antidiuretic hormone, or SIADH, is a disorder of impaired water excretion (which causes water retention) caused by excessive secretion of antidiuretic hormone (ADH).

• ADH secretion results in a reduced volume of concentrated urine. Urine osmolality is above 100 mosmol/kg.  SIADH is characterized by dilutional hyponatremia, and sodium is also lost as the body attempts to compensate for fluid volume excess with further sodium excretion. 

• For most patients, ingestion of water alone does not suppress ADH. The extra water intake leads to fluid volume excess, causing lower plasma sodium concentration by dilution.

• Outcomes of treatment include increased serum sodium (to 130 meq/L or higher), to reduce urine concentration, and to increase the volume of urine output.

• The treatment of hyponatremia in SIADH focuses on the underlying disease and therapies to raise and maintain the serum sodium. Causes of SIADH that can be treated include adrenal insufficiency, hypothyroidism, and infections including meningitis, pneumonia, and tuberculosis.

• Fluid restriction to under 800 ml/day is the goal for most patients. The goal is to bring serum sodium to 130 meq/L or higher.

• Hypertonic saline or sodium chloride oral salt tablets PO may be administered to replace sodium.

• Loop diuretics may be used to reduce urinary concentration, thereby increasing water excretion. 

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