WATER AND SODIUM DISORDERS FOLLOWING SURGICAL EXCISION OF PITUITARY REGION TUMORS

A prospective observational study of the pathophysiology of sodium and water disorders in patients with pituitary region rumours after surgi cal excision was carried out in 20 patients. Serial pre-operative and post-operative fluid and sodium balance, plasma and urine elctrolyte b iochemistry and their derived parameters, and circulating hormones ass ociated with fluid balance, atrial natriureic peptide (ANP) and antidi uretic hormone (ADH) were documented to correlate with the patients' c linical conditions. Ten out of these twenty cases developed diabetes i nsipidus (DI) requiring ADH replacement therapy, although in the major ity (6 cases), this way only a transient event. Of the nine patients w ho developed hyponatraemia, six had symptoms such as impaired consciou sness and convulsions. Four patients developed alternating hypoatraemi a and hypernatraemia, which constituted a difficult group, where appro priate sodium and fluid management, and ADH replacement therapy were b ased upon twice daily plasma and urine biochemistry and their derived parameters. Whilst DI in this group of patients was the result of a lo w circulating ADH level, hyponatraemia was not associated with an exag gerated ADH activity (6.0 +/- 2.3 vs 7.4 +/- 2.3 pmol/ml, mean+/-SEM). Rather, hyponatraemia was strongly associated with an elevated circul ating ANP concentration (82.3 +/- 10.5 vs 30.0 +/- 3.1 pmol/ml, mean /- SEM, p < 0.001), resulting in salt wasting and hypovolaemia.