Isotonic saline solution has the same osmolarity (particle density) as blood plasma. It is an electrolyte solution (crystalloid liquid solution) containing sodium and chloride (also called NaCl or common salt). An isotonic saline solution contains 9g of sodium chloride per liter of water (9g/l). Common salt is the most commonly used infusion solution because it is very inexpensive and easy to prepare.
Physical background
The human body contains sodium in an amount of about 135-145 mmol/l. 97% of it is outside the cell (extracellular), 3% inside the cell (intracellular). Sodium is an important component for the build-up of electrical tension on the cell membranes.
There it serves to transmit impulses and is an essential component of our body for muscle work. Sodium fulfils another important task in the distribution of water in the body. Like sodium, chloride is an electrolyte and also regulates the transmission of nerve impulses and intervenes in the water balance. The chloride content in serum is 98-109 mmol/l.
Composition and production
Isotonic saline solution consists of 154 mmol/l sodium and 154 mmol/l chloride. The concentration of sodium and chloride ions in isotonic saline solution is significantly higher than in the body. This higher dose is necessary because in the body not only sodium and chloride determine the osmolarity (particle density) of the blood.
The osmolarity of the resulting solution is about 309 mOsm/l and its pH value is between 4.5 and 7.0. Sodium chloride (common salt) is added to distilled water (purified water) during production. It can be said that 1 liter of 0.9% saline solution contains exactly 9 grams of sodium chloride (table salt).
Isotonic saline solution can be used as a carrier solution or diluent for medicines. Furthermore, it is used in everyday clinical practice to keep open or flush venous accesses, catheters or wounds. The eyes and nose are also rinsed with saline solution. Rehydration is another field of application for the isotonic saline solution. Here, severely dehydrated patients are administered saline solution to achieve volume substitution (restoration of the water content in the body).
