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Normal saline solution (0.9% NaCl) is considered isotonic with blood (although it actually has a slightly higher degree of osmolality). Ringers lactate is also considered isotonic.
5% Dextrose solution is also considered hypotonic compared with blood, because although it is isotonic while infusing, the dextrose is metabolized and free water is left, which is hypotonic.
Isotonic solutions are ones that contain a solvent, such as water, and a solute, such as table salt. The ions of salt have an ionic bond, sodium plus chloride. A saline solution is therefore...
A simplified definition of an isotonic solution is one that is the same "saltiness" a reference, usually the human body. So, for example, 0.9% salt in water is isotonic to human tears.