Alterations in plasma concentrations of natriuretic peptides and antidiuretic hormone after subarachnoid hemorrhage.

Objective: Hyponatremia is a common complication after subarachnoid hemorrhage. In this study we investigated the relations among hyponatremia, plasma natriuretic peptides, and antidiuretic hormone concentrations after subarachnoid hemorrhage.

Methods: Blood samples for radioimmunoassay measurement of plasma brain natriuretic peptide-like immunoreactivity, atrial natriuretic peptide-like immunoreactivity, and antidiuretic hormone were obtained every 2 to 4 days until day 14 after subarachnoid hemorrhage.

Results: Eleven of 20 patients with verified subarachnoid hemorrhage demonstrated mild hyponatremia (126 mEq/L < serum sodium < 135 mEq/L) during their clinical course. Atrial natriuretic peptide and antidiuretic hormone concentrations were significantly elevated on days 0 to 2 after onset of subarachnoid hemorrhage. Atrial natriuretic peptide concentrations remained high in patients who developed mild hyponatremia on days 6 to 14 after onset of subarachnoid hemorrhage. In contrast, antidiuretic hormone concentrations became significantly lower during the second week in these patients.

Conclusions: Mild hyponatremia after subarachnoid hemorrhage may be attributable not to the syndrome of inappropriate secretion of antidiuretic hormone but to cerebral salt-wasting syndrome. Atrial natriuretic peptide may be a causal natriuretic factor in cerebral salt-wasting syndrome.