A healthy 36-year-old man underwent transsphenoidal resection of a pituitary macroadenoma, which had been discovered incidentally on brain magnetic resonance imaging. In the immediate postoperative period, he received a 0.9% saline infusion as part of routine postoperative treatment. Within 30 minutes of arrival in the recovery room, he developed persistent, large-volume urine output (400 mL/h). Blood testing performed 6 hours after the operation showed a sodium value of 148 mEq/L, increased from a baseline level of 138 mEq/L. Complete laboratory results are found in the Table.
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A. Administer desmopressin
Hypernatremia is defined as plasma sodium concentration greater than 145 mEq/L and represents an increase in the quantity of sodium relative to the volume of water in the extracellular fluid.1 An increase in plasma sodium level is sensed by osmoreceptors in the hypothalamus, causing release of arginine vasopressin (AVP) from the posterior pituitary and stimulating thirst. AVP binds to the vasopressin 2 receptors in the kidney collecting ducts, leading water to flow from the tubular lumen to the surrounding interstitium, producing a small volume of concentrated urine. Hypernatremia resolves with ingestion of water and can persist if an individual has a defect in sensing thirst, an inability to obtain water, or both.1
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CME Disclosure Statement: Unless noted, all individuals in control of content reported no relevant financial relationships. If applicable, all relevant financial relationships have been mitigated.
Corresponding Author: Ziv Harel, MD, MSc, 61 Queen St E, Seventh Floor, Toronto, ON M5C 2T2, Canada (email@example.com).
Conflict of Interest Disclosures: Dr Kamel reported receiving royalties from Elsevier for publication of a textbook outside the submitted work. No other disclosures were reported.
Additional Contributions: We thank Kimberly Mah-Poy, MD (Division of Endocrinology, St. Michael's Hospital, University of Toronto), for providing the case information (not compensated). We also thank the patient for granting permission to publish this information.
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