In medicine, saline is a general term referring to a sterile solution of sodium chloride (table salt) in water, frequently used for intravenous infusion, rinsing contact lenses, nasal irrigation, and the yogic practice called jala neti. Saline solutions are available in various formulations for different purposes. Salines are also used in cell biology, molecular biology and biochemistry experiments. Normal saline is a solution of 0.9% w/v of NaCl (this nomenclature is confusing - "normal sodium chloride" to a chemist means a concentration of 5.85% w/v, also expressed as 1N NaCl(aq) ). It contains 154 mEq/L of Na+ and Cl−. It has a slightly higher degree of osmolality (i.e. more solute per liter) compared to blood (hence, though it is referred to as being isotonic with blood in clinical contexts, this is a technical inaccuracy), about 300 mOsm/L. Normal saline (NS) is therefore used frequently in intravenous drips (IVs) for patients who cannot take fluids orally and have developed severe dehydration. Normal saline is typically the first fluid used when dehydration is severe enough to threaten the adequacy of blood circulation and is the safest fluid to give quickly in large volumes.
Other concentrations of saline are frequently used for other medical purposes, such as supplying extra water to a dehydrated patient or supplying the daily water and salt needs ("maintenance" needs) of a patient who is unable to take them by mouth. Because infusing a solution of low osmolality can cause problems, intravenous solutions with reduced saline concentrations typically have dextrose (glucose) added to maintain a safe osmolality while providing less sodium chloride. As the molecular weight (MW) of dextrose is greater, this has the same osmolality as normal saline but contributes less sodium to the circulation. Because dextrose monohydrate (MW 198 in contrast to MW 180 for glucose) is the commercial form of dextrose used in these preparations, 5% dextrose actually contains only 4.5 g/dL of glucose.
The amount of normal saline infused depends largely on the needs of the patient (e.g. ongoing diarrhea or heart failure) but is typically between 1.5 and 3 litres a day for an adult.