Normal saline solution
Normal saline (NS) is the commonly-used term for a solution of 0.9% w/v of NaCl, about 300 mOsm/L. Less commonly this solution is referred to as physiological saline or isotonic saline, neither of which is technically accurate. NS is used frequently in intravenous drips (IVs) for patients who cannot take fluids orally and have developed or are in danger of developing dehydration or hypovolemia. NS is typically the first fluid used when hypovolemia is severe enough to threaten the adequacy of blood circulation and has long been believed to be the safest fluid to give quickly in large volumes. However, it is now known that rapid infusion of NS can cause metabolic acidosis [1] . NS is 9g NaCl dissolved in 1 liter water. The mass of 1 milliliter of NS is 1.009 grams. The molecular weight of sodium chloride is approximately 58 g/mole, so 58g NaCl is 1 mole. Since NS contains 9 grams NaCl, the concentration is 9g/L divided by 58g/mole = 0.154 mole/L. Since NaCl dissociates into two ions – sodium and chloride – 1 molar NaCl is 2 osmolar. Thus, NS contains 154 mEq/L of Na+ and Cl−. It has a slightly higher degree of osmolarity (i.e. more solute per litre) than blood (hence, though it is said to be isotonic with blood in clinical contexts, this is a technical inaccuracy).
Other concentrations commonly used include
1. Half-normal saline (0.45% NaCl), often with “D5” (5% dextrose), contains 77 mEq/L of Na and Cl and 50 g/L glucose. 2. Quarter-normal saline (0.22% NaCl) has 39 mEq/L of Na and Cl and always contains 5% dextrose for osmolality reasons. 3. Dextrose (glucose) 4% in 0.18% saline is used sometimes for maintenance replacement. (WikiDoc)
