Hyponatremia as a risk factor for microvascular spasm following subarachnoid hemorrhage.

Hyponatremia is a water-electrolyte balance disorder diagnosed in about 30% of patients after subarachnoid hemorrhage (SAH). The main factors responsible for hyponatremia in these patients are increased plasma concentrations of either vasopressin (leading to water retention and dilutional hyponatremia) or natriuretic peptides (leading to plasma sodium ions deficiency). Data demonstrates that the leading causes of post-SAH disability - delayed cerebrovascular spasm (CVS) and delayed cerebral ischemia (DCI) - are more often diagnosed in patients who develop hyponatremia than in normonatremic patients with SAH. Data also indicates that reducing sodium ion concentration in the blood/perfusate affects the tone and regulation of cerebral blood vessels in a manner that depends on the vessel's location in a vascular tree (intraparenchymal arterioles vs. large vessels on the brain surface) and environmental conditions. In the present article, we review possible mechanisms underlying the effects of hyponatremia on cerebral blood vessels and discuss the potential role of hyponatremia in the development of large vessels and microvascular spasm, taking into consideration the presence of vasopressin and natriuretic peptides.