Approach Considerations
Fluid replacement
Most patients with diabetes insipidus (DI) can drink enough fluid to replace their urine losses. When oral intake is inadequate and hypernatremia is present, replace losses with dextrose and water or an intravenous (IV) fluid that is hypo-osmolar with respect to the patient’s serum. Do not administer sterile water without dextrose intravenously, as it can cause hemolysis.
To avoid hyperglycemia, volume overload, and overly rapid correction of hypernatremia, fluid replacement should be provided at a rate no greater than 500-750 mL/h. A good rule of thumb is to reduce serum sodium by 0.5 mmol/L (0.5 mEq/L) every hour. The water deficit may be calculated on the basis of the assumption that body water is approximately 60% of body weight.
Desmopressin and other drugs
In patients with central DI, desmopressin is the drug of choice. [37, 38] A synthetic analogue of antidiuretic hormone (ADH), desmopressin is available in subcutaneous, IV, intranasal, and oral preparations. [39] Generally, it can be administered 2-3 times per day. Patients may require hospitalization to establish fluid needs. Frequent electrolyte monitoring is recommended during the initial phase of treatment.
Alternatives to desmopressin as pharmacologic therapy for DI include synthetic vasopressin and the nonhormonal agents chlorpropamide, carbamazepine, clofibrate (no longer on the US market), thiazides, and nonsteroidal anti-inflammatory drugs (NSAIDs). Because of side effects, carbamazepine is rarely used, being employed only when all other measures prove unsatisfactory. NSAIDs (eg, indomethacin) may be used in nephrogenic DI, but only when no better options exist.
In central DI, the primary problem is a hormone deficiency; therefore, physiologic replacement with desmopressin is usually effective. Use a nonhormonal drug for central DI if response is incomplete or desmopressin is too expensive.
Monitoring
Monitor for fluid retention and hyponatremia during initial therapy. Follow the volume of water intake and the frequency and volume of urination, and inquire about thirst. Monitor serum sodium, 24-hour urinary volumes, and specific gravity. Request posthospitalization follow-up visits with the patient every 6-12 months. Patients with normal thirst mechanisms can usually self-regulate.
Dietary measures
No specific dietary considerations exist in chronic DI, but the patient should understand the importance of an adequate and balanced intake of salt and water. A low-protein, low-sodium diet can help to decrease urine output.
Precautions
Patients with DI must take special precautions, such as when traveling, to be prepared to treat vomiting or diarrhea and to avoid dehydration with exertion or hot weather. Patients should ensure access to water at their destination when traveling. Travels through deserts are best undertaken at night to avoid the excessive dehydration that can occur during day travel.
Postoperative Setting
After pituitary surgery, patients should undergo continuous monitoring of fluid intake, urinary output, and specific gravities, along with daily measurements of serum electrolytes. [40] In patients who develop DI, administer parenteral desmopressin every 12-24 hours, along with adequate fluid to match losses.
Follow the specific gravity of the urine, and administer the next dose of desmopressin when the specific gravity has fallen to less than 1.008-1.005 with an increase in urine output. When the patient can tolerate oral intake, thirst can become an adequate guide.
In patients with DI who have undergone surgery of any kind, administer the usual dose of desmopressin and give (hypotonic) IV fluids to match urinary output.
Consultations
In the setting of neurosurgery or head trauma, the diagnosis of DI may be obvious, and even expected. The intensivists and nurses who manage the patient acutely are in the best position to provide acute care.
In the more subtle forms of DI, and certainly in all chronic forms of DI for which therapy is expected to be indefinite, the clinical endocrinologist is an invaluable aid in establishing the diagnosis and designing therapy.
Medical genetics consultation is appropriate if there is a family history of DI and an inherited form is suspected.
