Hypernatremia

1. Serum Na > 150; most often seen in neurosurgical patients in the setting of diabetes insipidus (DI), and in patients who have received repeated doses of osmotic diuretics to treat intracranial hypertension
2. Normal total body water is 60% of the patient’s weight thus (20% is extracellular and 40% is intracellular)
   1. current TBW=140 x normal TBW (e.g. 70 kg x .6 = 42)/current Na
   2. water deficit = normal TBW – current TBW

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