Why is a tourniquet placed 3-4 inches above the intended puncture site?

When placing an intravenous (IV) line, a tourniquet should not be placed near the needle puncture site. Instead, place a tourniquet 3-4 inches _below_ the puncture site to make the vein prominent or engorged with blood.

Applying a tourniquet directly at the IV site can make cannulation of the vein almost impossible due to tissue compression (making puncture and visualization of vessels difficult) and potential venous collapse when the tourniquet is released.