HyponatremiaE87.1

Common electrolyte disturbance that occurs when the plasma sodium concentration is < 130 mmol/L. Hyponatremia simply means that the sodium concentration is too low in relation to the extracellular volume, but there is not necessarily a sodium deficiency.

Depending on the hydration status of the patient, the following forms can be distinguished:

• Hypervolemic hyponatremia: total body sodium excess in the presence of water excess.
• Hypovolaemic hyponatraemia: total body sodium deficiency with extracellular volume deficiency: Isovolaemic hyponatraemia: total body sodium in the normal range

The cause is usually an unbalanced water balance due to a disturbance of ADH-mediated water excretion, i.e. free water cannot be excreted renally. This can either be triggered by medication due to an increased ADH release and effect, occur in the course of the syndrome of inadequate ADH secretion or also be the consequence of liver cirrhosis, heart failure or volume deficiency.

Furthermore, the sodium balance is influenced by extrarenal sodium and fluid loss, e.g. in diarrhoea, as well as by renal loss, as in diuretic therapy.

Symptoms are more likely to occur with more severe or even rapid onset hyponatremia and range from nausea and muscle weakness to clouding of consciousness, grand mal seizures, and coma.

Causal; treatment of the underlying disease

Symptomatic: in acute hyponatremia: infusion of 100 ml of a 3% NaCl solution.