Most of the intravenous solutions are isotonic to the blood plasma.
The intravenous solutions are directly injected into the blood of the individual. So, it is very important that the solution must be isotonic to the blood plasma.
In case, the blood plasma and intravenous fluid are not isotonic, then the cells present in the blood plasma may shrink or swell due to the change in the osmolarity of the plasma. This can hamper the normal functioning of the blood cells.