Water and sodium disorders following surgical excision of pituitary region tumours

A prospective observational study of the pathophysiology of sodium and water disorders in patients with pituitary region tumours after surgical excision was carried out in 20 patients. Serial pre-operative and post-operative fluid and sodium balance, plasma and urine elctrolyte biochemistry and their derived parameters, and circulating hormones associated with fluid balance, atrial natriureic peptide (ANP) and antidiuretic hormone (ADH) were documented to correlate with the patients' clinical conditions. Ten out of these twenty cases developed diabetes insipidus (DI) requiring ADH replacement therapy, although in the majority (6 cases), this way only a transient event. Of the nine patients who developed hyponatraemia, six had symptoms such as impaired consciousness and convulsions. Four patients developed alternating hypoatraemia and hypernatraemia, which constituted a difficult group, where appropriate sodium and fluid management, and ADH replacement therapy were based upon twice daily plasma and urine biochemistry and their derived parameters. Whilst DI in this group of patients was the result of a low circulating ADH level, hyponatraemia was not associated with an exaggerated ADH activity (6.0 ± 2.3 vs 7.4 ± 2.3 pmol/ml, mean ± SEM). Rather, hyponatraemia was strongly associated with an elevated circulating ANP concentration (82.4±10.5 vs 30.0 ±3.1 pmol/ml, mean ± SEM, p < 0.001), resulting in salt wasting and hypovolaemia.