Diabetes Insipidus

Diabetes Insipidus (DI) is caused by a lack of antidiuretic hormone (ADH) which results in the inability of the kidneys to retain water.

Etiology and Physiology
ADH is made in the hypothalmus and secreted by the posterior pituitary. It exerts its effect on the kidneys resulting in water retention and more concentrated urine.

DI can be either primary or secondary. If primary the cause is ideopathic or unknown. Secondary DI is usually the result of trauma or disease affecting the hypothalmus or pituitary gland such as tumors, physical trauma, neurosurger or CNS infection, It is also possible for ADH levels to be adequate and for the kidneys to be unable to respond appropriately.

Signs and Symptoms
A water restriction test is done to confirm a diagnosis of DI. The nurse obtains vital signs, weight, urine specific gravity, urine and serum osmolalities. The patient is then restricted from all fluids for 8-16 hours. Assess weight, vitals and urine osmolality hourly. Test is considered positive if urine osmolality does not increase. Stop the test if bodyweight declines by 3%, orthostatic hypotension or tachycardia develops.
 * Polyuria - Urine output of 5 - 20 Liters a day.
 * Polydipsia - Excessive thirst to compensate for water lost through urinating.
 * Specific gravity of urine will be between 1.001 and 1.005. Normal ranges are 1.005 and 1.020. This is because kidneys cannot concentrate urine without adequate ADH.
 * Hypernatremia. Water is lost but Na is not leading to an increase in Na+. Effectes of this include agitation, restlessness, seizures and decreased reflexes.
 * Weight loss
 * Constipation
 * Poor skin turgor

Treatment
Medication

Desmopressin acetate (DDAVP) is the drug of choice in replacing ADH. LIke ADH it causes the kidneys to retain water. It can be given PO, IV, Sub-Q or intranasally. Assess urine specific gravity, weight gain, hyponatremia, headache, restlessness, fluid I&O. Notify provider if urine specific gravity falls below 1.005.

Diabenese is a medication used to treat DM that also had antidiuretic effects and can be used to treat DI. Other medication used are hydrochlorothiazide and chlorothiazide (both diuretics), tegretol, and vasopressin both of which decrease the amout of water secreted in urine.

Surgery

If it is necessary to remove the pituitary gland a transphenoidectomy may be done. This involves removing the pituitary gland through an incision behind the upper lip through the gum line. If this is done the nurse should monitor for infection (meningitis), visual disturbances, and glucose in nasal drainage (nasal bib test) as this is indictive of cerebralspinal fluid leakage and should be reported to the physician. Head of the bed should be in high fowlers. Pain is generally minimal.