Trick question, it's both a hypotonic and hypertonic fluid.
When initially infused it is hypertonic but the dextrose is quickly metabolized leaving just the .45NS w/ KCL which at that point becomes a hypotonic fluid pushing free water from the intravascular space into the cells.
Think about dehydration, the first step is to correct the intravascular deficit (usually with LR or NS) if it is an isotonic dehydration (which most often is) and a maintenance fluid is given such as D5 1/2NS to push fluid from the intravascular space into the cells.
This is why D5 1/2NS (with or without the KCL) is almost never a first line fluid for rehydration.
What sort of disease processes/diagnoses would D5 1/2NS+KCl be used with? Anyone have experience using it with their patients?
Very common maintenance fluid used in treating dehydration. You treat dehydration in phases. I have a feeling I am wandering into homework territory but figure that the D5 is metabolized quickly and it leaves the 1/2NS with 20KCL to hydrate.