A tourniquet is a constricting or compressing device used to control venous and arterial circulation to an extremity for a period of time. Pressure is applied circumferentially upon the skin and underlying tissues of a limb; this pressure is transferred to the walls of vessels, causing them to become temporarily occluded. Tourniquets.orgSurgical tourniquets enable surgeons to work in a bloodless operative field.Emergency tourniquets are used in emergency bleeding control to prevent severe blood loss from limb trauma.