What is meant by isotonic?

You have 60 % of water in your body. 40% in the intro-cellular compartment and 20 % in the Extra cellular compartment. So it comes to be 40 liters in a 'Average' man weighing 70 kg.It means 28 liters in intro-cellular and 14 liters in extra cellular compartment. Human body has carried with it the part of sea, probably as a extra cellular compartment.Isotonic means that tonicity of fluid equal to body fluid.In extra cellular compartment, Sodium chloride is present mainly. It contains 'about' 150 mili mole of Sodium chloride.One mole of Sodium chloride contains 58.5 gram/liter of it.Mass number of Sodium being 23 and that of Chlorine is 35.5. So added together it makes 58.5 gram/liter. One mole of Glucose contains 180 grams/ liter. (C 6 H 12 O 6 means 12*6 plus 1*12 plus 16* 6, it means mass numbers of the respective elements.) (It means 1000 mili mole/liter.) So 9 gram/liter or 0.9 % of sodium chloride or 0.9 gram/100 ml, makes Isotonic saline solution. So Isotonic solution is compatible with 'Human' normal saline solution.It will neither make cells to shrink nor swell. So 0.45 % Sodium chloride solution is Hypo-tonic and 0.9% Sodium chloride with 5 % Glucose solution is Hyper-tonic.(In your body, Glucose will be rapidly utilized to give energy and you get Isotonic saline solution.) Normal saline solution means in which 1 mole of molecules dissolve/ liter and is a term used in chemistry. So when you say Normal saline, it means it contains 58.5 gram/liter of sodium chloride and will kill the patient in no time, after few infusions. So previously human normal saline and then 'Isotonic' saline solution is the correct term to be used. The normal saline solution available in market is not "Normal'. It is 'Isotonic' solution.