Sodium and Water Regulation after Pituitary Surgery: Results of a Prospective Pilot Study of Early Postoperative Water Load

Objective Disorders of water balance, such as diabetes insipidus (DI) and delayed hyponatremia, account for most readmissions after transsphenoidal pituitary surgery. Despite numerous studies, no consistent risk factors have been identified. We instituted a prospective protocol including an early postoperative water load to better understand sodium and water balance and to identify patients at risk for unplanned readmission for these conditions.

Methods Fifteen patients were prospectively enrolled in the study. All patients underwent transsphenoidal pituitary tumor resection, and sodium levels were monitored postoperatively in the intensive care unit. On the morning of postoperative day (POD) 1, patients with normal serum sodium and no clinical suspicion for DI were administered an oral water load based on body weight. Serum sodium, vasopressin levels, and urine output were recorded. Patients were followed up for 14 days after surgery.

Results Of the 15 patients enrolled, 13 patients successfully completed the water load on the morning of POD 1. The other two patients were excluded due to hypernatremia. No significant adverse events were encountered. Three patients developed transient DI; two of these patients later developed delayed postoperative hyponatremia after discharge (nadir serum sodium levels, 121 and 132 mmol/L). One of these patients was readmitted for hyponatremia (nadir serum sodium level, 121 mmol/L). The remainder of patients remained normonatremic throughout the study period. Mean serum sodium levels 6 hours after water loading were significantly higher for patients who developed subsequent DI (144 vs. 139.8 mmol/L, p < 0.001). Six-hour urine output greater than 120% of the water load reliably predicted which patients would develop subsequent DI (100% sensitivity, 100% specificity).

Conclusion An early postoperative water load was safe and well tolerated on POD 1 after transsphenoidal pituitary surgery. This protocol may help identify patients at risk for sodium imbalance in the postoperative period and may help guide outpatient management strategies in the future.