what about surgical touniquets?

would you even know if they were used?

Surgical tourniquets prevent blood flow to a limb and enable surgeons to work in a bloodless operative field. This allows surgical procedures to be performed with improved precision, safety and speed. Tourniquets are widely used in orthopedic and plastic surgery, as well as in intravenous regional anesthesia (Bier block anesthesia) where they serve the additional function of preventing local anesthetic in the limb from entering general circulation.

http://en.wikipedia.org/wiki/Surgical_tourniquet

i only copied part of the post on wiki.