Disturbed Osmoregulation: Pituitary-Associated Hyponatremia

NOVEMBER 25, 2013
Jeannette Y. Wick, RPh, MBA, FASCP
A retrospective review of hyponatremia associated with pituitary surgery found that intervention with pharmaceuticals is significantly more effective than measures designed to replace sodium or deplete water.

Syndrome of inappropriate antidiuretic hormone secretion often follows pituitary surgery. Headache, dizziness, nausea, and vomiting can complicate otherwise successful surgical recoveries. Patients frequently must be readmitted, inconveniencing them and increasing costs for payers.
Researchers at the University of California, San Francisco, performed a retrospective review of pituitary operations to determine the frequency of hyponatremia and examine the efficacy of several different interventions in those patients who developed hyponatremia.
The researchers examined 1045 consecutive pituitary surgeries performed at a dedicated pituitary center starting in 2008. As a standard practice, surgeons had ordered preoperative and daily inpatient sodium checks for all surgical candidates, with outpatient checks as needed. The researchers published their results online on August 23, 2013, in the Journal of Neurosurgery.
Thirty-two patients (3%) presented with preoperative hyponatremia, and 41% of them were symptomatic. Almost 60% of patients with preoperative hyponatremia required medical correction before surgery. Of the patients who had preoperative hyponatremia, 18 (56%) went on to have postoperative hyponatremia as well.
In all, 165 (16%) patients developed postoperative hyponatremia, with a median development time of 4 days after surgery (range 0-28 days). In the group that developed postoperative hyponatremia, slightly less than 1 in 5 reported symptoms, with dizziness, nausea, and vomiting most commonly reported. Of the patients who developed postoperative hyponatremia, 15% were readmitted due to hyponatremia.
The researchers performed a multivariate analysis to determine whether various factors increased one’s risk for developing hyponatremia. These factors included lesion size, age, sex, number of prior pituitary surgeries, surgical approach, pathology, lesion location, and preoperative hypopituitarism. Of these, only preoperative hypopituitarism was positively and significantly associated with postoperative hyponatremia.
Interventions for patients who developed hyponatremia included no treatment, free water restriction, salt tablets, 3% saline, an intravenous vasopressin receptor antagonist (conivaptan), or an oral vasopressin receptor antagonist (tolvaptan). Preoperative hypopituitarism was most efficiently managed with conivaptan or tolvaptan. Other interventions produced outcomes that were not significantly different from no intervention. Postoperative hyponatremia was most efficiently managed with oral tolvaptan.
The researchers note that the trends they observed indicate that postoperative hyponatremia is often a transient, self-correcting phenomenon. In pre- and post-operative hyponatremia, measures designed to replace sodium or deplete water are no more effective than no intervention. Intervention with pharmaceuticals is significantly more effective.
Ms. Wick is a visiting professor at the University of Connecticut School of Pharmacy and a freelance writer from Virginia.

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