Well, all that I can offer is know that is a number seems just a little high, as far as an IV running XXX mL/ hr, patients, with heart or renal issues, can not handle the volume, b/c the heart is too weak and the kidneys can't perfuse respectively. You also want to watch for this in babies and the elderly, they just can't handle the volume.
Next, you know 0.9% NS is isotonic, so it will stay where it is put. This is what will be running if a pt is or has the potential of becoming hypovolemic, b/c they need the volume in the vascular space, to prevent going into shock.
Hypotonic solutions, are hydration, that go wherever, rehydrate and move on to be burned up by cellular metabolism.
And hypertonic are packed with particles of some kind. TPN (hyperalimentation) has a buch of nutrient particles of course b/c it is total nutrition (pts still need water). Also, things like D50 packed with sugar, for hypoglycemic patients whose blood sugar has bottomed out (they would probably unconscious at this point). And 3.5% or 5% NS, for pts who are severely hyponatremic.
I hoped I helped, and you are not even more confused.