PATHOGENESIS OF HYPONATREMIA FOLLOWING SUBARACHNOID HEMORRHAGE DUE TORUPTURED CEREBRAL ANEURYSM

BACKGROUND Hyponatremia following subarachnoid hemorrhage (SAH) occurs due to the inappropriate secretion of antidiuretic hormone (SIADH). H owever, this condition is also sometimes associated with certain dehyd ration states. METHODS To clarify the pathogenesis, daily values of ur ine volume, water balance, and sodium balance (Na Bal) were correlated with plasma levels of atrial natriuretic peptide (ANP), antidiuretic hormone (ADH), and plasma renin activity (PRA) in 31 cases of SAH. RES ULTS Na Bal was markedly negative on days 2 and 3. Cumulative Na Bal s howed continuous negative values until day 10 following SAH. ANP value s showed a consistent elevation, while ADH showed only an initial surg e. PRA, as the gross indicator of circulatory volume, showed a lack of suppression, indicating no increase in the circulatory volume. CONCLU SION Hyponatremia following SAH therefore appears to be the result of increased natriuresis, due to the inappropriate elevation of ANP rathe r than SIADH. In this situation, water restriction should not be recom mended, since the circulatory volume is decreased. (C) 1996 by Elsevie r Science Inc.