Severe hyponatraemia: current concepts on pathogenesis and treatment.

Severe hyponatraemia (serum sodium <120 mEq/L) is a serious electrolyte disorder associated with life-threatening neurological complications. It develops most often when the ability of the kidney to excrete free water is impaired. The initial adaptation of the brain to hyponatraemia includes loss of water, sodium, potassium and chloride into the cerebrospinal fluid and the late adaptation consists of the loss of organic osmolytes. Adaptation of the brain to hyponatraemia causes potential problems during therapy, as re-adaptation requires a considerably longer time. Rapid correction of hyponatraemia may lead to the development of the osmotic demyelination syndrome. Though the ideal treatment for severe hyponatraemia remains controversial, a consensus regarding therapeutic guidelines has emerged. The rate of correction and the type of infusate depend on the duration and cause of the hyponatraemia, clinical presentation, volume status, renal function and the serum potassium level. The prognosis of the osmotic demyelination syndrome is rather dismal although several therapeutic modalities have been tried.