NCLEX Review Guide: Antidiuretic Hormones

Mechanism of Action

• ADH (Vasopressin) is produced in the hypothalamus and stored in the posterior pituitary gland. It regulates water reabsorption in the kidneys by increasing permeability of collecting ducts, leading to concentrated urine and decreased urine output.
• ADH release is triggered by increased plasma osmolality, decreased blood volume, or stress situations. Normal ADH levels maintain fluid balance and prevent dehydration.

Diabetes Insipidus (DI)

• Central DI results from ADH deficiency due to hypothalamic or pituitary damage. Nephrogenic DI occurs when kidneys don't respond to ADH despite normal levels.
• Classic symptoms include polyuria (3-20L/day), polydipsia, and risk of severe dehydration with hypernatremia if fluid intake is restricted.

SIADH (Syndrome of Inappropriate ADH)

• Excessive ADH secretion causes water retention, dilutional hyponatremia, and concentrated urine despite low serum osmolality. Common causes include CNS disorders, lung cancer, and certain medications.
• Key lab findings: low serum sodium (<135 mEq/L), low serum osmolality, high urine osmolality, and high urine sodium despite hyponatremia.

Desmopressin (DDAVP)

• Desmopressin is synthetic ADH analog used for central diabetes insipidus, primary nocturnal enuresis, and hemophilia A. Available as nasal spray, tablets, or injection with longer duration than natural ADH.
• Monitor for water intoxication, hyponatremia, and headache as adverse effects. Dosing is individualized based on urine output and serum sodium levels.

DDAVP Administration Steps

1. Assess baseline vital signs and fluid status
2. Monitor urine output and specific gravity
3. Check serum sodium levels regularly
4. Educate patient on proper nasal spray technique
5. Monitor for signs of water intoxication

Assessment and Monitoring

• Monitor strict intake and output, daily weights, and vital signs to assess fluid balance. Document urine specific gravity and color to evaluate concentration ability.
• Watch for signs of dehydration (DI) or fluid overload (SIADH) including changes in mental status, skin turgor, and mucous membrane moisture.