A tourniquet is a device that is used to apply pressure to a limb or extremity in order to limit – but not stop – the flow of blood. It may be used in emergencies, in surgery, or in post-operative rehabilitation. A tourniquet is also used by the phlebotomist to assess and determine the location of a suitable vein for venipuncture. Proper application of a tourniquet will partially impede venous blood flow back toward the heart and cause the blood to temporarily pool in the vein so the vein is more prominent and the blood is more easily obtained. The tourniquet is applied three to four inches above the needle insertion point and should remain in place no longer than one minute to prevent hemoconcentration.