In a popular Star Trek TNG episode, three terminally ill people are frozen and when discovered by the Enterprise are revived and cured. Doctors in London are ready to go to human trials and a somewhat less extreme procedure to do the same thing. The process is for treating people who are minutes away from dying due to a catastrophic loss of blood. This means gunshots, knife wounds, deep cuts etc. The patient’s blood is replaced with a cold saline solution, bringing the body temperature from 98.6 to 50 in a few minutes. This induces hyporthermia, like when someone falls into an icy river. The person has no heartbeat or brain activity. Doctors then operate to repair the injuries and revive the patient. They say it works 90% of the time on pigs.
Why does this work? In normal operation, the brain and body would use up all the oxygen in the blood (what’s left of it). When low on oxygen the mechanism that generates energy releases destructive freeoxygen that damages the cells. A person would die within 4-5 minutes. In a hypothermic patient, this would take 90-120 minutes to happen.
Obviously, this would only be used as a last resort for someone who is about to die anyway.