Post-Operative Water Load Following Transsphenoidal Pituitary Surgery

Delayed post-operative hyponatremia occurs in 5-20% of patients following pituitary surgery and typically occurs on post-operative day 5-10.This decline in sodium can occur rapidly and have serious consequences such as altered mental status, seizures, coma, and even death. Despite significant research into patient demographics and risk factors, the investigators have not been able to predict which patients will suffer from delayed post-operative hyponatremia to date. At the Barrow Neurological Institute, physicians currently utilize an outpatient screening protocol to monitor patients' sodium levels after surgery, but this has yet to be effective for reducing readmissions following pituitary surgery. The etiology of delayed post-operative hyponatremia has been linked to water and sodium dysregulation in the post-operative period. It has been shown that post-operative day 1-2 sodium levels are statistically lower in patients who develop delayed hyponatremia, however, the numerical differences are not large enough to guide clinical management. The investigators propose that a water load on post-operative day 1 may expose underlying sodium/water dysregulation in the early post-operative period. This would improve physicians' understanding of the pathophysiology of post-operative hyponatremia, and it may help to serve as a screening tool for these patients in the future.

Current standards are for screening of all post-operative transsphenoidal pituitary patients for sodium abnormalities in the POD(post-operative day)7-14 window. At the Barrow Neurological Institute, physicians have instituted a universal screening protocol for all post-operative patients wherein all patients have a serum sodium level drawn on POD5-7 and attempts are made to manage mild to moderate hyponatremia on an outpatient basis.This screening protocol has effectively identified delayed post-operative hyponatremia, however, it has yet to reduce readmissions for hyponatremia in these patients. The researchers propose that implementing a water load test on POD1 may facilitate outpatient screening in three ways: 1) The water load may identify a subset of patients who have appropriate water and sodium regulation after surgery and do not require close monitoring of outpatient sodium levels. 2) The water load may identify a subset of patients who are at risk for delayed hyponatremia and would benefit from strict counseling and closer outpatient monitoring. 3) The water load may identify a subset of patients with a moderate to severe reduction in serum sodium in response to the water load, and these patients may benefit from further monitoring in the hospital prior to discharge. If any of these scenarios hold true, this may change the way physicians monitor and treat patients following transsphenoidal surgery in the future. Furthermore, this protocol could be readily expanded to other neurosurgery practices and could facilitate care for future patients undergoing transsphenoidal pituitary surgery.

All enrolled subjects passing conditions outlined in Intervention are eligible to be included. WL will be calculated (20 mL/kg body weight) and supplied at the bedside. Patient will have 30 minutes to consume WL, or will be excluded.

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.

Evaluate patients' responses to water load on the morning of post-operative day 1: serum sodium (normal range 135-145 mmol/L)

Evaluate patients' responses to water load on the morning of post-operative day 1: serum osmolality (normal range 275-300 mOsm/kg)

Evaluate patients' responses to water load on the morning of post-operative day 1: urine output (normal range > 0.5 ml/kg/hr)

Evaluate patients' responses to water load on the morning of post-operative day 1: vasopressin level (normal range 0.0 - 6.9 pg/ml)

Follow patients' serum sodium levels after discharge from the hospital and assess for any correlation in water load response and outpatient sodium levels. This is not done with a mathematical calculation but by observation of lab results. Hypothetically, normal water load response (serum sodium =135-145) will equate to normal outpatient sodium levels (135-145). Likewise, an abnormal water load response (sodium < 135 or >145) will equate to possible abnormal outpatient sodium levels (< 135, >145).

Inclusion Criteria: 18-80 years of age Functioning or non-functioning pituitary adenoma Sodium level 135-145 prior to surgery Exclusion Criteria: Enrolled in a separate pituitary research study Unable to provide his/her own consent Unable to take PO water Renal insufficiency Require maintenance corticosteroids pre-operatively TSH secreting tumor Patients who the treating surgeon deems a poor candidate for the water challenge Prisoners Pregnant women

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