Osmolarity: Definition

Osmolarity is the sum of the molar concentration of all osmotic particles per unit volume of a solution. These osmotically active substances include primarily calcium, chloride, glucose, urea, potassium, magnesium, and sodium. Thus, physiological serum osmolarity depends almost exclusively on sodium concentration. Osmotic changes in the other electrolytes are not compatible with life.

The unit is osmol/l.

The determination of osmolarity is used to control the water and electrolyte (blood salt) balance of the body. A distinction is made between:

Hyperosmolarity (hyperosmolar) – in this case, there is a greater number of dissolved particles per liter of fluid than in the reference fluid.
Isoosmolarity (isoosmolar) – here is the same number of dissolved particles.
Hypoosmolarity (hypoosmolar) – here the number of dissolved particles is less than in the reference liquid per liter of liquid.

The method

Material needed

Preparation of the patient

Disruptive factors

Because of standard values – see osmolality [In medicine, osmolality is usually used!].

Interpretation of elevated values (osmolality/sodium elevated).

Dehydration (lack of fluid) – decrease in the amount of blood circulating in the circulation; caused by decreased fluid intake or increased fluid losses:
- Diarrhea (diarrhea; especially in children and the elderly).
- Severe vomiting
- Heavy sweating (hyperhidrosis)
- Polyuria (increased urine output; > 1.5-3 l / day)
Hyperhydration (hypervolemia with hypernatremia (excess sodium), hematocrit (share of all cellular components in the volume of blood/erythrocytes make up about 95% of it) ↓):
- Excessive saline intake:
  - Iatrogenic (caused by a physician).
  - Primary hyperaldosteronism (Conn syndrome)
- Increased sodium reabsorption:
  - Impaired renal function
Renal diabetes insipidus (synonym: ADH– or vasopressin-resistant diabetes insipidus).
Central diabetes insipidus (synonym: diabetes insipidus neurohormonalis) – the cause is an absence or insufficient production of antidiuretic hormone (ADH) – the cause is a defect in the kidney, which despite the presence of the hormone ADH can not form a normally concentrated urine

Interpretation of decreased values (osmolality / sodium normal / decreased).

Ethanol intoxication (alcohol intoxication).
Hyperglycemia (high blood sugar)
Lactic acidosis – form of metabolic acidosis/metabolic acidosis in which a drop in blood pH is due to the accumulation of acidic lactate.
Uremia (occurrence of urinary substances in the blood above normal values).

Notes