[Hypo- and hypernatremia in the intensive care unit : Pitfalls in volume management]

Hypo- and hypernatremias are very frequent in intensive care unit (ICU) patients and are closely related to volume disturbances and volume management in the ICU. They are associated with longer ICU stays and significant increases in mortality. Treating them is more complex than it may initially appear. Hyponatremias are differentiated based on tonicity and volume status. With hypertonic and isotonic hyponatremias, the primary focus of treatment is the underlying hyperglycemia. In case of hypotonic hypovolemic hyponatremia, the condition is treated with balanced crystalloid solutions. In eu-/hypervolemic hypotonic hyponatremias acute treatment with hypertonic saline is necessary. Hypervolemic hypernatremia occurs almost exclusively in ICU patients, often due to infusion of hypertonic solutions. There is little evidence to guide treatment, although hypotonic infusions in conjunction with diuretics may represent a legitimate approach. Great emphasis should be placed on prevention and the infusion of hypertonic solutions should be avoided. Disturbances in plasma sodium concentrations are common, requiring close attention. Exact diagnostic classification needs to be made and volume managed accordingly.