Excess sodium (hypernatremia) - causes, symptoms and therapy

Causes and signs of hypernatremia

Sodium is the most common electrolyte in the human body. It is found primarily in the blood and extracellular fluid. Together with potassium, sodium is the most important element for regulating the fluid balance. It is also relevant to the heart rhythm and functionality of nerves and muscles and has an impact on blood pressure.

A balanced mixture ratio between sodium and liquid is necessary for the regulation of the fluid balance and the other functions. Certain mechanisms can change this relationship and cause the concentration of sodium in the blood to increase. This condition is called hypernatremia when the sodium level in the blood serum exceeds 145 mmol / L. It is usually between 135 and 145 mmol / L.

An excessive concentration can arise in two ways. Either too much sodium or too little water is supplied to the body or it loses too much fluid. The higher sodium concentration in the extracellular space ensures that water is extracted from the cells, following the osmotic pressure drop. They shrink and lose their function. Depending on the mechanism of the sodium excess, there may be different variants of the blood composition.

A lack of fluid causes the blood volume to decrease and the sodium content to increase relatively. In this case, one speaks of hypernatremia with hypovolaemia. With an increased sodium intake, however, the blood volume increases (hypervolemia) because the excess sodium binds a lot of water.

Causes of Hypernatremia

The most common cause of hypernatremia is a lack of fluid in the blood, which can basically arise in two ways. Either too little fluid is ingested or too much is excreted. The elderly, children and intubated patients are at risk for people who are unable to drink and dehydrate. This creates a discrepancy between fluid consumption and intake. The reasons for this can be very different.

Children often forget to drink and ignore their thirst. This also applies to older people. They may also experience a disturbed feeling of thirst and the fact that they are not able to provide sufficient water on their own. The latter often applies to intubated and seriously ill patients. In all cases, the result is insufficient fluid intake. A lack of fluid develops in the blood, which leads to a relative increase in the sodium level, although the absolute amount of sodium has not increased.

The second mechanism that can lead to hypernatremia is massive fluid loss. This can be caused by diarrhea as a result of an infection, severe vomiting, excessive sweating, as a result of burns, exhalation in the event of a fever or by taking water-laxing medications (diuretics).

Patients suffering from diabetes insipidus are also affected. In this condition, which is also called water urinary dysfunction, a deficiency in the antidiuretic hormone aldosterone or a functional disorder of the kidney is responsible for the increased fluid excretion. As a result, the organ is no longer able to concentrate the urine. The thin urine is excreted quickly and in large quantities. Even with these processes, which are associated with increased fluid loss, the absolute amount of sodium in the blood does not change, only its concentration. All forms of hypernatremia described so far are associated with hypovolaemia.

In rare cases, an excess of sodium in the blood can also be caused by an increased intake of sodium. On the one hand, this can be the result of a high-salt diet combined with drinking liquids that contain a lot of sodium. The second way to ingest too much sodium is to increase the electrolyte supply through sodium-rich infusions. This type of hypernatremia, in which sodium is increasingly taken up, is always associated with hypervolemia due to the high ability of sodium to bind water. With mild forms, the blood volume can remain approximately the same (normovolaemia).

Symptoms of excess sodium in the blood

The symptoms that occur with hypernatremia are caused by the change in the concentration gradient between the extra and intracellular space. Outside the cell, the sodium content increases, while it initially remains the same in the cell. This removes liquid from the cell. It dehydrates, shrinks and loses function. In this way, symptoms develop that are initially very general and non-specific. They can also be associated with other diseases. This is why hypernatremia is often difficult to diagnose at first.

Typical signs can include intense thirst, tiredness, weakness, restlessness and lack of concentration. Edema, mostly in the legs, can also occur. Another characteristic of prolonged sodium excess can be signs of desiccation such as standing skin folds and deep-set eyes. The symptoms are usually discovered by chance in the course of routine laboratory diagnostics. With prolonged sodium excess and severe course, dehydration of the cells, particularly in the brain and heart, has serious consequences. An increase in the sodium concentration above 180 mmol / L means life-threatening. The following list lists neurological and other symptoms that can occur with hypernatremia:

  • Increase in muscle reflexes,
  • muscular fasciculations,
  • Cramps,
  • Seizures,
  • Headache (cephalgia),
  • Apathy,
  • Hyperexcitability of the nervous system (hyperexcitability),
  • Tremor,
  • Confusion,
  • Coma,
  • Respiratory failure,
  • high blood pressure
  • and irregular heartbeat


A thorough medical history is the primary diagnostic tool for diagnosing hypernatremia. It can be used to answer questions about drinking behavior, eating habits and possible previous illnesses. Possible causes of fluid loss such as diarrhea and vomiting can also be asked. During this conversation, the doctor can get important information that justifies a suspicion of excess sodium.

In a subsequent examination, the doctor tests blood pressure, vigilance and whether there are signs of dehydration or neurological changes. He examines the skin turgor and the signs of desiccation by looking at the tongue moisture, the condition of the mucous membranes and the behavior of the skin folds. In the neurological area, tests of the muscles' own reflexes and the checking of alertness and mental functions are part of the examination spectrum. The primary diagnosis is finally made in the laboratory by determining the serum sodium value.

During the course of treatment to compensate for fluid deficiency by infusion, this test is repeated to verify the success of the substitution. If the compensation does not lead to a satisfactory result from the laboratory values, this indicates that the cause of the fluid deficit has not yet been discovered and corrected. In this case, further differential diagnostic tests must follow to find out the underlying disease.

Other diagnostic methods used for diabetes insipidus or unsuccessful fluid balancing are the determination of the urine volume and the concentration of dissolved particles in the blood and urine (osmolality).


In many cases, hypernatremia can be remedied by replacing the lack of fluids. This can be done orally or intravenously. If the balance is made by infusion, a sodium-free glucose solution is given, which also contains minerals to normalize the electrolyte balance.

The glucose binds sodium ions in the blood and removes them from the body so that they are excreted in the urine. The compensation should, however, take place slowly, so that the adaptation processes of the organism can proceed in a timely and risk-free manner. The persistent excess of sodium has manifested itself in the cells as a lack of fluid. If the sodium level is lowered too quickly due to the fluid intake, the osmotic conditions change so that there is a rapid influx of water into the cells. They swell and can put pressure on the surrounding tissue. This can be particularly dangerous in the brain. As a result of the swelling of the cells, brain edema forms, which can compress the brain mass due to the limited ability of the skull to expand. Depending on the location, the neurological symptoms described above can be triggered.

In the case of cerebral edema, the supervision of therapy by a doctor is strongly recommended. In many cases, the therapy for hypernatremia, in addition to fluid substitution, is the treatment of the causative disease. Infections that cause diarrhea or vomiting can usually be treated with medication. If there is an excess of sodium, the administration of a diuretic may also be useful in order to regulate the fluid balance and to avoid edema.

The reverse is the case with diabetes insipidus. With this disease, antidiuretic drugs (desmopressin) can be administered to reduce the increased water excretion and ideally to normalize it. There are often difficulties with the renal form of the disease because the kidneys do not respond to the active ingredients. Patients suffering from diabetes insipidus are definitely advised to change their diet. You should eat a low-salt and low-protein diet.

The importance of changing diet and living conditions

In some people, there is a risk that hypernatremia can occur again and again. This affects people who are unable to provide adequate hydration due to their age or illness. In older people, this is not only due to a lack of physical ability, but also to a reduced feeling of thirst. In such cases, it is important that strategies are developed together with the doctor on how the adequate intake of water can be regulated. Partners, relatives and caregivers should also be included in the concept.

How much sodium the human body actually needs is not precisely defined. However, there is an upper limit that is recommended for the daily intake of table salt. It is six grams per day in adolescents and adults. Because of the close relationship between high sodium levels and high blood pressure, medical professionals advise you not to consume more than three to four grams per day. Many people in Germany take a significantly higher dose with their food. The average intake is nine grams per day. On the one hand, this has to do with the fact that lifestyle and eating habits have changed.

On the other hand, the additional intake of table salt is offset by a lack of exercise. The excretion of sodium through sweating is eliminated. On the other hand, nutritional awareness and composition have changed. In times of fast food and finished products, many people no longer know which foods contain how much salt. They have no overview and no control over the amount of salt they consume every day. Many are also not aware of the dangers of this diet because the effects are not immediately noticeable. Education work in this area is therefore important.

It is known that such drinking and eating habits have negative effects on health and, in extreme cases, can contribute to the development of hypernatremia. If sodium-containing drinks and a high-salt diet are the cause of an increased sodium content in the blood, it is important to change your eating and drinking habits. In this case, nutritionists can be included in the treatment concept. They make it clear to those affected what they should pay attention to when preparing the food and which drinks and foods are suitable for a low-sodium diet. Foods rich in table salt include, for example, sausages, chips, vegetable juices, cheese, ready-made soups and sodium-rich mineral water. On the other hand, little table salt contains teas, milk, sweets, eggs and low-sodium mineral water.

When it comes to changing eating and drinking habits, people in need of support also need support. Older people, small children and the seriously ill are unable to ensure an adequate diet. That is why the inclusion of the surrounding people in the nutritional concept is important. (fp)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Dipl. Geogr. Fabian Peters, Dr. med. Andreas Schilling


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Video: High Sodium, Hypernatremia, symptoms, treatment, management, cause, correction of hypernatremia (January 2022).