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PANCE Practice Exam 2

Terms in this set (300)

The answer is C.
EXPLANATION: The patient presents with a combination of inadequate fluid intake and excessive losses due to perspiration, resulting in hypovolemia and hypernatremia. The most common causes of hypernatremia are inadequate fluid intake resulting in hemoconcentration and diabetes insipidus (DI), resulting in excessive renal fluid losses. Normal urine osmolality is 500 to 850 mOsm/kg but can range from 50 to 1,200 mOsm/kg depending on the patient's fluid intake. Urine osmolality >400 mOsm/kg indicates that the renal fluid-conserving mechanism is intact, as the kidneys are working to preserve volume. A lower urine osmolality would be consistent with DI, characterized by a lack of response to anti-diuretic hormone (ADH), resulting in excessive urinary losses of water with worsening hypernatremia. Treatment is directed at the cause. If the patient is dehydrated, restoring fluid volume is the goal. If the patient has DI, treating the underlying disease will lower the serum sodium level. For this dehydrated patient, the treatment would be to administer isotonic (normal) saline, which contains 0.9% sodium, because of the large free water deficit. Quarter-normal saline contains 0.25% sodium, half-normal saline contains 0.45% sodium, and lactated Ringer's solution is similar to half-normal saline in its sodium content. Dextrose 5% in water (D5W) contains no electrolytes. Isotonic saline is the appropriate choice because it treats not only the volume deficit but the serum osmolality as well. Its osmolality (308 mOsm/kg) is often lower than the plasma osmolality because of the hypovolemic state and, therefore, helps restore normal serum osmolality. Once serum osmolality becomes more normal, the isotonic saline can be replaced by D5W to replace the remaining free water deficit. If the free water deficit were less dramatic, initial IV fluid treatment could be half-normal saline, followed by D5W.