osmolarity and tonicity

Hyperosmotic is refer to the solution that contains more "stuff" than its environment. Let's take your cell as an example. Your cell does not allow a lot of material to leave. So, when you have a solution that is isomotic, you can have a solution that is isotonic to the cell (in every shape or form) or hypotonic to the cell in other aspect. So why does IV being look at as isotonic to the cell? This is weird. IV contain "stuff" that is similar to your blood (i.e. your extracellular). When you have put an IV in, you tend to just fill up that extra cellular part, and not the intracellular part. Hence, you see people look a tad big!
So, in explaining what you are thinking, the question you should be asking is, is that substance osmotically active? Does it contribute to the osmolarity of the liquid in question?
Hope that helps.