Osmolarity

The osmolarity is the measure to express the total concentration (measured in osmoles/liter) of substances in solutions used in medicine. The prefix "osmo-" indicates the possible variation of the osmotic pressure in the cells, which will occur when the solution is introduced into the organism. In osmolality (see that it is different from osmolarity), the concentration is expressed as osmoles per kilogram of water, also referring to some specific substances.

Osmotic concentration, commonly known as osmolarity, is a measure of the concentration of solutes, defined as the number of osmoles (Osm) of a solute per liter (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed in Osm/L (pronounced Osmolar), in the same way that the molarity of a solution is expressed as "M" (pronounced Molar"). While molarity measures the number of moles of a solute per unit volume of a solution; Osmolarity measures the number of participating osmoles of solute per unit volume of a solution.

Examples

The normal osmolarity of body fluids per liter of solution is similar to a 0.9% NaCl solution.

A solution or dissolution of 0.1 M NaCl would give 0.1 moles of Na⁺ and 0.1 moles of Cl^– per liter, its osmolarity being 0,2. If this solution is injected into a patient, his cells would absorb water until equilibrium was reached, causing a variation in blood pressure.

Blood osmolarity (mOsm/L) = 2 Na⁺ + k + Glucemia (mg/dL)/18 + BUN (mg/dl)/2.8