[Differential diagnosis of hyponatremia following subarachnoid hemorrhage]

Hyponatremia is a common complication after subarachnoid hemorrhage (SAH). Although the mechanism of hyponatremia is still controversial, cerebral salt-wasting syndrome (CSNS) is currently regarded as being more responsible than the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). The aim of our study was to assess the plasma volume status of a patient with hyponatremia following subarachnoid hemorrhage. In doing this it may be possible to indirectly differentiate its pathogenesis. Fifty patients with SAH were studied. Twenty patients demonstrated hyponatremia (serum sodium < 135 mEq/L) during day 7 to 13 after subarachnoid hemorrhage. Patients with hyponatremia were categorized on the basis of their daily body weight, and central venous pressure. Group A consisted of patients with hypovolemia (16 patients), with the onset time of hyponatremia being day 7 to 9. Group B included those with hypervolemia (4 patients); hyponatremia was observed during day 10 to 11 and was corrected in all patients within 72 hours after induction of fluid restriction. Our findings suggest that hyponatremia following subarachnoid hemorrhage usually occurs due to CSWS, although SIADH remains as a minor pathogenesis. We conclude that the combination of daily body weight and CVP measurements is a simple and practical method to distinguish promptly SIADH from CSWS.