Postoperative delayed hyponatremia after endoscopic transsphenoidal surgery for pituitary adenomas: role of fluid restriction and associated risk factors

Background – Delayed postoperative hyponatremia remains a frequent complication after endoscopic endonasal transsphenoidal surgery (EETS) for pituitary adenomas and is a major cause of hospital readmission. Although fluid restriction has emerged as a potential preventive strategy, evidence regarding its efficacy and associated predictive factors remains limited. This study aimed to evaluate the impact of a standardized postoperative fluid-restriction protocol on the incidence of postoperative delayed hyponatremia and to identify factors associated with postoperative delayed hyponatremia development. Methods – A retrospective cohort study was conducted including 222 patients who underwent EETS for pituitary adenomas between January 2025 and January 2026. Patients with preoperative diabetes insipidus or requiring postoperative desmopressin treatment were excluded. Patients treated before implementation of routine postoperative fluid restriction constituted the non–fluid-restricted group (n=120), whereas patients treated after protocol implementation received fluid restriction of 1000 mL/day for 7 postoperative days (n=102). Delayed postoperative hyponatremia was defined as serum sodium <135 mmol/L occurring after postoperative day 3. Clinical, radiological, endocrine, and biochemical variables were analyzed. Results – Delayed postoperative hyponatremia developed in 30 patients (13.5%). The incidence was significantly lower in the fluid-restricted group than in the non–fluid-restricted group (6.9% vs 19.2%, p=0.013). Mean onset of delayed postoperative hyponatremia was postoperative day 7.9, and 93.3% of affected patients required readmission. Delayed postoperative hyponatremia development showed no significant association with age (p=0.963), sex (p=0.810), body mass index (p=0.446), tumor diameter (p=0.505), Knosp grade (p=0.350), extent of resection (p=0.289), adenoma subtype (p=0.267), or remission status (p=0.735). In contrast, suprasellar extension (p=0.010), postoperative pituitary hormone deficiency (p=0.001), preoperative hypothyroidism (p=0.033), diaphragma sellae descent (p<0.001), lumbar drainage (p<0.001), and sodium decline ≥3 mEq/L (p=0.002) were significantly associated with delayed postoperative hyponatremia. Multivariate logistic regression identified preoperative comorbidities (p=0.002), postoperative diaphragma sellae descent (p=0.029), postoperative hypothyroidism (p=0.011), postoperative hypokalemia (p=0.002), and longer hospital stay (p<0.001) as independent predictors of delayed postoperative hyponatremia. Conclusions – Routine postoperative fluid restriction significantly reduced the incidence of delayed postoperative hyponatremia following EETS for pituitary adenomas. Early postoperative sodium changes and selected perioperative factors may help identify high-risk patients and improve postoperative monitoring strategies.