Post-Operative Water Load Following Transsphenoidal Pituitary Surgery

Patient will have normonatremic 0600 hr sodium level (Serum Sodium = 135 - 145 mmol/L), ability to safely take water by mouth, and cleared to continue by treating surgeon. WL will be calculated (20 mL/kg body weight) and supplied at the bedside. Vasopressin level will be determined. Patient will have 30 minutes to consume WL, or will be excluded. Included patients will have data collected as follows: 1 hour - serum sodium, urine output; 2 hour - serum sodium, urine output, vasopressin level; 6 hours - serum sodium, urine output.