Introduction: Hyponatremia, usually attributed to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), typically occurs in a delayed fashion following transsphenoidal surgery.

Methods: 207 patients, 129 females and 78 males, with the mean age of 44.6 underwent transsphenoidal surgery in our institution between January 2012 and July 2013. We determined the incidence and risk factors of postoperative SIADH. Clinical features, tumor size, endocrinological activity, hyponatremic symptoms, daily postoperative urine volume, Body Mass Index (BMI), postoperative serum sodium levels were investigated. We compared BMI, gender between the patients with SIADH and without SIADH. We also compared postoperative daily serum sodium levels and daily urine volume between with and without SIADH. We tried to determine the threshold level of BMI which predicts the postoperative SIADH. Early prophylactic water restriction was performed for high risk patents.

Results: Incidence of postoperative SIADH was correlated with BMI and it was statistically significant and the threshold value of BMI which predicts SIADH was 26. Serum sodium level of the patients at postoperative day of 5 to 9(Nadir day 8), urine volume of day 7 to 10, degree of body weight reduction of the patients with SIADH were significantly lower compared with those of patients without SIADH. The overall incidence rate of SIADH was 64 cases, 33%. Before starting the early prophylactic water intake restriction, the rate of SIADH occurrence was 38%, and it was significantly lower compared with the occurrence of SIADH after prophylactic water intake restriction of 14% (p<0.05).

Conclusions: SIADH is common event following transsphenoidal surgery, and serum sodium concentration and daily urine volume should be carefully monitored. Attention must be paid to a low preoperative BMI, as this factor was significant preoperative risk factor of SIADH. Early prophylactic water intake restriction is effective to prevent postoperative SIADH.

Patient Care: This study contributes to the patients to avoid complication of SIADH and shorten the duration of hospitalization

Learning Objectives: The goal of this study is to assess the incidence, risk factors of SIADH in patients that underwent transsphenoidal surgery, and effectiveness of early prophylactic water intake restriction.

References: 1. Hussain NS, Piper M, Ludlam WG, Ludlam WH, Fuller CJ, Mayberg MR. Delayed postoperative hyponatremia after transsphenoidal surgery: prevalence and associated factors. J Neurosurg 119: 1453-1460, 2013 2. Kelly DF, laws ER Jr, Fossett D: Delayed hyponatremia after transsphenoidal surgery for pituitaryadenoma. Report of nine cases. J Neurosurg 83: 363-367, 1995