Severe symptomatic hyponatremia (serum Na < 110–115 mmol/l) which develops within less than 48 hours is a life–threatening complication because of seizures and other symptoms of brain oedema. Its rapid correction to normal values is mandatory and is connected with minimal risk of neurologic sequalae. On the contrary, in case of symptomatic hyponatremia which developed chronically, rapid correction is indicated only to ameliorate symptoms. Too rapid correction may cause severe neurologic deragements – osmotic demyelinisation syndrome (ODS). Incidence of brain injury due to rapid changes in osmolarity is in intensive care patients very likely more frequent than currently anticipated. As CT scan of the brain is frequently negative, NMR seems to be a method of choice in imaging of areas of demyelinisation in typical brain stem and basal ganglia localisations.

        Key words: hyponatremia – demyelinisation – infusion therapy – critically ill – intensive care