A 25-year-old man, frozen within a snow drift, has been “brought back to life” by doctors after they initially thought he was dead. Justin Smith was ice-cold to the touch, and paramedics assumed he had succumbed to severe hypothermia. However, as reported by The Washington Post, after a last-ditch effort to restart his heart, he was saved against all odds in a first for medical science.

Last February, Smith was found almost entirely covered by snow on the side of an empty road. The coroner, arriving at the scene, thought that he had been lying there, in temperatures of -20°C (-4°F), for 12 hours. He checked for a pulse and found nothing. The man's body temperature was not even registering using a digital thermometer.

Smith was flown by helicopter to Lehigh Valley Hospital. The team of doctors and nurses there tried to warm him up and restart his heart using cardiopulmonary resuscitation (CPR), but to no avail. Gerald Coleman, the emergency department physician on duty at the hospital, decided to give Smith a potassium test.

Potassium is vital for the communication between nerves and muscles, including within the heart. A high concentration within the bloodstream indicates that the heart muscle activity is significantly reduced; in Smith’s case, this would mean his heart was very unlikely to restart. When the results came back normal, however, the hospital thought he had a chance.

Using a technique called extracorporeal membrane oxygenation (ECMO), warm, oxygenated blood was passed into Smith’s heart and through to the rest of his body; it was effectively an artificially beating heart. Improbably, his heart began to quiver, or “fibrillate.” Doctors then managed to shock his heart into restarting.

Ventilators were used to breathe for him, and the ECMO procedure was continued for some time. Medical staff thought he might have been brain-dead, but scans designed to pick up on the electrical signals given off by neurological activity came back entirely normal. He awoke from his coma, and a year on, apart from losing his toes and little fingers to frostbite, Smith, as reported by BBC News, is a completely healthy individual.

“No human being should be able to survive the cold and a body temperature of 18°C (64°F) and a lack of pulse for 12 hours – but Justin Smith did,” John E. Castaldo, chief of the division of neurology within the Lehigh Valley Health Network, said in a network-produced video.

The secret to his survival lies in the body’s ability to slow down its metabolism – the process that converts oxygen and nutrients into energy. For every degree celsius that the body temperature drops, metabolism drops as much as 7 percent. This means that, at colder temperatures, cells in the body require less oxygen, and the heart rate begins to slow, conserving the body’s energy.

Even though Smith’s internal body temperature meant that his heart had apparently stopped beating, his body had cooled at just the right rate to allow his metabolism to adapt, operating at minimal levels. The medical staff recognized this, and brought him back to life from his state of suspended animation.

He is the coldest person known to medical science to have survived such extreme hypothermia, and scientists are still not entirely sure how his brain was left completely undamaged.