Hyponatremia in critical illness

Hyponatremia is the commonest electrolyte disorder in hospitalized patients and is associated with increased morbidity and mortality. Although most patients are asymptomatic at presentation, many present neurological symptoms which can easily be overlooked and have the potential to progress and produce neurological sequelae, and even death, if not diagnosed and treated promptly. The classification of hyponatremia is based on serum osmolality and the volume status of the patient. When iatrogenic causes are excluded, inadequate secretion of antidiuretic hormone and cerebral salt wasting are the commonest mechanisms of hyponatremia in neurological and critically ill patients and their differentiation is crucial because they require drastically different management. The risks of overly rapid correction (which mostly comprise osmotic demyelination) must be borne in mind when treating hyponatremia. Management mainly depends on the speed of onset of hyponatremia and the presence of symptoms. Vasopressin antagonists have recently been introduced into clinical practice with promising results. More randomized studies are needed to determine the optimal role of these new agents in the treatment of hyponatremia.