Delayed Hyponatremia Following Surgery for Pituitary Adenomas: An Under-recognized Complication

Background: Delayed hyponatremia is a serious complication seen after pituitary surgery. We document the incidence, presentation, outcome and risk factors for this condition. Materials and Methods: This was a retrospective study involving 222 patents operated for nonfunctioning pituitary macroadenomas between 2007-2016. Delayed hyponatremia was defined as serum sodium c135 mmol/L, occurring after the third post-operative day. Hyponatremia was categorized as mild (134-130 mmol/L), moderate (129-125 mmol/L) and severe (<125 mmol/L). All patients received intravenous (0.9%) saline, intravenous hydrocortisone and 12g oral salt over 24 hours. Patients with severe hyponatremia were given 3% saline. Results: Fifty eight patients (26%) developed delayed hyponatremia; thirty (13.5%) had severe hyponatremia. Delayed hyponatremia usually (43.1%) occurred on the seventh post-operative day (range, 3-15 days). Most patients (81%) remained asymptomatic; 11 patients developed vomiting (5), seizures (3), lethargy (1), fever (1) and paralytic ileus (1). One patient developed status epilepticus. Patients who manifest symptoms had lower sodium levels as compared to those who did not have symptoms (mean 117.7 mmol/L vs. 123 mmol/L; P < 0.01). Male gender (P = 0.002) and intra-operative CSF leak (P = 0.003) were risk factors for developing delayed hyponatremia. Other factors like, age, pre-operative cortisol levels, extent of resection and post-operative diabetes insipidus did not correlate with the occurrence of delayed hyponatremia. Patients who maintained their mean serum sodium levels >138 mmol/L (day 1 day 3) were unlikely to develop delayed hyponatremia (sensitivity, 55.2% and specificity, 83.9%), positive predictive value, 63.2% [confidence interval (CI) 48, 76.7%] and negative predictive value, 78.8% (CI 70.6, 85.5%). In most patients (57%) hyponatremia was corrected within 48 hours (h). Conclusions: We recommend routine serum sodium testing on the seventh post-operative day for all patients undergoing pituitary surgery. Most patients remain asymptomatic and unless they are detected early they can go on to develop serious complications.