Hyponatremia in the patient with subarachnoid hemorrhage.

Hyponatremia commonly occurs in patients with aneurysmal subarachnoid hemorrhage. Two mechanisms have been proposed as causes: syndrome of inappropriate anti-diuretic hormone and cerebral salt wasting. Physical examination and laboratory results can assist a clinician in identifying which mechanism is responsible and thus determine proper treatment. When hyponatremia is treated promptly and appropriately, patients' sodium levels return to normal without detrimental effects.