Hypernatremia is a common electrolyte disorder that reflects an imbalance in the water balance of the body, often resulting from an increased loss of free water compared to sodium excretion. It is rarely based on excessive sodium intake. The clinical presentation is often characterized by a central nervous system dysfunction (confusion, coma) and pronounced thirst (in awake patients). In addition to medical history, the volume status of the patient and the osmolality of urine are leading in the differential diagnosis. Usually, the treatment of hypernatremia - in addition to addressing the underlying cause - is replacing the (absolute or relative) loss of free water by hypotonic infusions, or in case of diabetes insipidus, by application of Desmopressin (Minirin). As rapid changes in serum sodium concentration may have deleterious consequences (osmotic demyelinsiation syndrome), preexisting hypernatremia (>48h) should not be reduced by more than 8-10 mmol/l/day. Close laboratory controls are important. For acute hypernatremia (< 24 hours), hemodialysis is an effective option to rapidly normalize the serum sodium levels. To avoid a rapid drop in sodium concentration that must also be considered when starting a renal replacement therapy in patients with chronic hypernatremia.
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