Intentional hypothermia is used in medicine in both regional and total-body cooling for organ and tissue protection, preservation, or destruction. Interrupted blood flow starves organs of oxygen and may cause permanent organ damage or death. The body's metabolic rate (the rate at which cells provide energy for the body's vital functioning) decreases 8% with each 1.8°F (1°C) reduction in core body temperature, thus requiring reduced amounts of oxygen. Total-body hypothermia lowers the body temperature and slows the metabolic rate, protecting organs from reduced oxygen supply during the interruption of blood flow necessary in certain surgical procedures. In some procedures, like heart repair and organ transplantation, individual organs are preserved by intentional hypothermia of the organ involved. In open heart surgery, blood supply to the chilled heart can be totally interrupted while the surgeon repairs the damaged organ. Organ and tissue destruction using extreme hypothermia - 212 to -374°F (-100 to -190°C) is utilized in retinal and glaucoma surgery and to destroy pre-cancerous cells in some body tissue. This is called cryosurgery.