I  n 1999 a 29-year-old physician fell headlong into a river while skiing in northern Norway.
      Friends watched helplessly as Anna Bagenholm was carried by currents and finally wedged beneath thick ice floes. More than an hour passed before she was pulled to shore. By then, she had no heartbeat and her core temperature had plunged to 57°F. Emergency crews started cardiopulmonary resuscitation and kept at it during the hour-long flight to Tromsø University Hospital. It took nine hours of treatment and slow warming before Bagenholm came to, and she spent 60 days in intensive care. Yet she was back at work within five months, and a year later she was skiing again.

Bagenholm hadn’t really died in the biological sense. Her heart had stopped, but like her other vital organs, including her brain, it was likely preserved by her extraordinarily low body temperature. Metabolism is governed in part by temperature, and as the body cools, its cells need less oxygen. At 57°F, with her metabolism slowed to just 10% of its baseline rate, Bagenholm needed practically none. She was in a quasi-hibernating state of suspended animation, poised between life and death.

Bagenholm isn’t the only person to have survived such an experience. In fact, these occasional medical “miracles” demonstrate the principles of what some physicians hope may become a powerful clinical tool. Medical researchers have induced suspended animation in animals by cooling them to superlow temperatures or giving them low levels of gases that safely slow metabolism under controlled conditions. Human trials may begin soon. It’s already possible to cool humans to extremely low temperatures and drain blood from the body to fix otherwise inoperable aneurysms. If progress continues, suspended animation could emerge as a way to save victims of heart attacks, central nervous system injuries and trauma. The aim, explains Patrick Kochanek, director of the Safar Center for Resuscitation Research at the University of Pittsburgh School of Medicine, is to pause metabolism while medical teams fix normally lethal injuries or make repairs that wouldn’t be feasible at normal body temperatures. “We want to suspend the body’s need for oxygen while we tend to the emergency,” Kochanek says.

The notion of protecting patients by cooling them isn’t new. In the early 1950s, Canadian cardiologist Wilfred Bigelow, a co-developer of the cardiac pacemaker, wrapped patients in cooling blankets and ice packs to push core body temperature to as low as 82° during heart surgery, allowing time to perform difficult procedures. Inducing even milder hypothermia, cooling patients to no lower than 91.4°, has since become almost routine during surgery for heart, brain and spinal cord injuries, among other applications. The cooler temperature helps prevent cell death in the affected tissue while physicians try to repair the damage.

But suspended animation requires profound hypothermia, a state in which body temperature is forced down to 50° or cooler, and inducing such a state has had its problems. Doctors couldn’t achieve rapid body cooling consistently using blankets and ice packs, and even cooling the blood by circulating it through heat exchangers connected to heart-lung bypass machines ran the risk of leaving some body parts too warm. Also, shivering was hard to control. Because of these challenges and others—including evidence of irreversible brain damage to children who were cooled to low temperatures to allow controlled cardiac arrest—hypothermia fell out of favor during the 1970s.

But in 1986, Robert Spetzler, now director of the Barrow Neurological Institute at St. Joseph’s Hospital and Medical Center in Phoenix, attempted a procedure in which he cooled a patient’s body to a very low temperature, using a variation on a technique first tried in the 1960s. In those days, surgeons opened the heart to attach a catheter, then cooled the blood by running it through a bypass machine to prepare for surgery; about half the patients died.