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Classification according to ICD-10
E87.0 Hyperosmolality and Hypernatremia
Sodium Excess
ICD-10 online (WHO version 2019)

With hypernatremia one is electrolyte imbalance with increased sodium concentration in the blood serum, respectively. It is associated with increased osmolarity and is an expression of a relative lack of water. The cause is usually the loss of water, which is hypertonic hypohydration ( desiccosis ), i.e. a disruption of osmoregulation . In rare cases, it is the result of increased sodium levels (due to Conn's syndrome or Cushing's syndrome ).

The water loss results from

  • Reduced fluid intake (particularly affects older people who feel less thirsty or cannot drink independently) or
  • increased water excretion (sweat, urine with diabetes insipidus or aquaresis , exhalation with fever, evaporation from burns).

When water is lost, the sodium level is normal or reduced, but the sodium concentration in the blood increases due to the lack of water. Even a small increase will induce severe thirst, usually followed by hydration to clear the hypernatremia.


Hypernatremia is often difficult to diagnose because the symptoms are rather diffuse. Those affected complain of a general feeling of weakness, tiredness and difficulty concentrating. Edema can also occur. In severe cases, epileptic seizures and loss of consciousness occur . In infants and newborns, it is not uncommon for hypernatremia to be found only through routine laboratory control. Otherwise, symptoms such as muscular hypotension, apathy, hyperexcitability, tremors, seizures or apnea appear.

Severe cases are when the sodium concentration in the blood plasma is above 158 mmol / l (normal values ​​are in the range 135 to 145 mmol / l). Values ​​above 180 mmol / l are life-threatening.


Hypernatremia is relatively easy to correct with hydration, either orally or intravenously . This must be done slowly, however, as a rapid decrease in the sodium concentration can be life-threatening. This is due to the fact that with prolonged hypernatremia, the water content in the cells also decreases. A rapid decrease in the sodium content in the serum would lead to an osmotic influx of water into the cells and cause them to swell. In the brain , this can lead to cerebral edema and, because of the cranial bone's limited ability to expand, to brain damage. Therefore, severe hypernatremia should always be treated by a doctor.

Individual evidence

  1. Michael Obladen et al. (Ed.): Newborn intensive care medicine. Springer, Heidelberg 2006, ISBN 3-540-33737-7 .