Hyponatremia – colloquially called sodium deficiency – (synonyms: absolute sodium deficiency; hyperhydration; hypervolemic hyponatremia; hyponatremia in euvolemia; hyponatremia in hypervolemia; hyponatremia in hypovolemia; hyponatremia syndrome; hypotonic hyperhydration; hypovolemic hyponatremia; isotonic hyponatremia; isovolemic hyponatremia; pseudohyponatremia; salt deficiency syndrome; salt wasting syndrome; dilutional hyponatremia; ICD-10-GM E87. 1: Hypoosmolality and hyponatremia) is when the concentration of serum sodium in an adult falls below a value of 135 mmol/l. Hyponatremia is classified on the basis of serum sodium concentration as follows:
- Mild hyponatremia: 130-135 mmol/l.
- Moderate hyponatremia: 125-129 mmol/l
- Severe hyponatremia: < 125 mmol/l
Physiological serum osmolarity depends almost exclusively on sodium concentration. Thus, hyponatremia is accompanied by hypoosmolality (hyperosmolarity).Osmolality is the sum of the molar concentration of all osmotically acting particles per kilogram of solvent. In hyperosmolality (hyperosmolal), there is a greater number of dissolved particles per kilogram of fluid than in the reference fluid. Absolute sodium deficiency:
- Renal (kidney-related) causes: e.g., due to salt-losing kidney, mineralocorticoid deficiency, diuretics (dehydrating therapy).
- Extrarenal (causes located outside the kidneys) sodium losses; e.g., due tovomiting, diarrhea (diarrhea), ileus (intestinal obstruction), peritonitis (peritonitis), pancreatitis (pancreatitis), burns, SIADH (syndrome of inadequate ADH secretion)
Forms of hyponatremia (for details, see below hyponatremia (sodium deficiency)/causes).
- Hypertonic hyponatremia: when there is an increased concentration of other osmotically effective substances, usually glucose. The osmotic gap is greater than 10 mosmol/L.
- Hyponatremia in polydipsia (excessive thirst).
- Hyponatremia in euvolemia (total body sodium in the normal range).
- Hyponatremia in hypovolemia (decrease in the circulating, i.e., in the bloodstream amount of blood).
- Hyponatremia in hypervolemia (increase in the volume of circulating, ie, located in the bloodstream).
The prevalence (frequency of disease) is about 7% outpatients and 15-30% inpatients. Course and prognosis: in hyponatremia, there are fluid shifts between the extracellular and intracellular space (extracellular space (EZR) = intravascular space (located inside the vessels) + extravascular space (located outside the vessels); intracellular space (IZR) = fluid located inside the body cells). There is an influx of fluid into the cells, with the result that cerebral edema (brain swelling) can occur.Symptoms can vary from mild and nonspecific to severe and life-threatening. Moderately severe symptoms include nausea without vomiting, headache, and confusion. Severe symptoms include vomiting, cardiorespiratory problems, seizures, confusion, and impaired consciousness (somnolence/drowsiness with abnormal drowsiness to coma/severe deep unconsciousness characterized by lack of response to address). The occurrence of cerebral symptoms depends on the extent of hyponatremia and its development over time. In slowly developing hyponatremia, cerebral symptoms do not occur until the serum sodium concentration is < 115 mmol/l. In contrast, cerebral edema in acute hyponatremia occurs at serum concentrations < 125 mmol/l.Patients with chronic hyponatremia are conspicuous for gait unsteadiness (gait disorder) and cognitive deficits.Treatment of hyponatremia is by correction of sodium balance (see “Drug therapy” below). Hyponatremia below 125 mmol/l is associated with mortality (number of deaths in a given period, relative to the number of the population concerned) of up to 30%.
