The causes of increased sodium in the blood (hypernatremia)

Hypernatremia is always associated with hyperosmolarity. When the osmolality of the plasma becomes higher than 290 mosm / L, an increase in the secretion of the antidiuretic hormone by the posterior lobe of the pituitary gland is observed. A decrease in the volume of extracellular fluid enhances this reaction, whereas an increase can weaken it. The reaction of the kidneys to the antidiuretic hormone is aimed at preserving free water in the body and consists in reducing diuresis.

Causes of hypernatremia (serum sodium concentration above 150 mmol / l):

• dehydration during water depletion (increased water losses through respiratory tract during shortness of breath, fever, tracheostome, artificial ventilation of lungs in conditions of insufficient moistening of the respiratory mixture, use of non-moistened oxygen, open treatment of burns, prolonged sweating without adequate water compensation); it is generally believed that an excess of every 3 mmol / L of sodium in the serum above 145 mmol / l means a deficiency of 1 liter of extracellular water;
• salt overloading of the organism (feeding through the probe with concentrated mixtures without adequate water injection for a long unconscious state, after operations on the brain, in connection with obstruction of the esophagus, feeding through the gastrostomy);
• diabetes insipidus (decreased sensitivity of the kidney receptors to antidiuretic hormone);
• kidney diseases occurring with oliguria;
• hyperaldosteronism (excessive secretion of aldosterone by an adenoma or a tumor of the adrenal glands).

The preferential loss of water compared with sodium leads to an increase in the osmolality of the plasma and the concentration of sodium, due to the decrease in the volume of circulating blood, the blood flow in the kidneys decreases and the formation of aldosterone is stimulated, which leads to sodium retention in the body. At the same time, hyperosmolarity stimulates the secretion of antidiuretic hormone and reduces the excretion of water in the urine. Depletion of water reserves is quickly restored if sufficient water is supplied to the body.

Depending on the violations of the water balance, which always accompany hypernatremia, the following forms are distinguished:

• hypovolemic hypernatremia;
• euvolemic (normovolemic) hypernatremia;
• hypervolaemic hypernatremia.

Hypovolemic hypernatremia can occur as a result of the prevailing loss of water compared to sodium losses. Loss of sodium with any body fluid, with the exception of intestinal and pancreatic juice, leads to hypernatremia (the total sodium content in the body decreases). The consequences of hypotonic fluid loss include hypovolemia (due to loss of sodium) and increased osmotic pressure of body fluids (due to loss of free fluid). Hypovolemia is a serious complication that can lead to hypovolemic shock.

Euvolemic hypernatremia occurs with diabetes insipidus and water loss through the skin and respiratory tract. Loss of water without loss of sodium does not lead to a decrease in the volume of fluid in the intravascular bed. In addition, hypernatremia does not develop unless the patient's water intake decreases.

There are two main variants of excess water diuresis (euvolemic hypernatremia) - central diabetes insipidus and nephrogenic diabetes insipidus.

In most patients with progressive chronic kidney disease, the ability of the kidneys to gradually concentrate urine is gradually impaired. In chronic renal failure of any etiology, it is possible to develop a decreased sensitivity to the antidiuretic hormone, which is manifested by the release of hypotonic urine. In the treatment of such patients who can still "form" urine, it is very important to remember that consumption of a certain amount of liquid is necessary for them, since it allows to influence the daily osmotic clearance by a non-invasive method. Restriction of fluid intake in such patients can lead to the development of hypovolemia.

Hypervolaemic hypernatremia, as a rule, develops as a result of the introduction of hypertonic solutions (for example, 3% sodium chloride solution), as well as correction of metabolic acidosis with intravenous sodium bicarbonate infusions.

Clinical manifestations of hypernatremia as such - thirst, trembling, irritability, ataxia, muscle twitching, confusion, convulsive seizures and coma. Symptoms are pronounced with a sharp increase in the concentration of sodium in the blood serum.