Medicine is warming to the technique of cooling patients in order to save them, writes Mary Fallon.

Eight years ago a Swedish medical registrar, Anna Bagenholm, found herself the subject of the medical textbooks she had been studying. Skiing with friends in a waterfall gully in northern Norway, she went off course and plunged head-first into the freezing river.

The 29-year-old was helpless against strong currents that wedged her under a thick ice floe. She did not drown because she was able to breathe in an air pocket, but her companions could not free her. After 40 minutes her struggling stopped. It was another 40 minutes before a hole was cut in the ice and she was pulled out. Her body temperature had dropped to 13.7 degrees.

But the cold was Bagenholm's salvation. While it had caused her heart to stop beating, the cold also preserved her vital organs, including the brain, in a state of deep hypothermia. After nine hours of resuscitation and rewarming, Bagenholm regained consciousness. Eight months later she was back at work with no lasting damage except for tingling in her fingers.

The lessons learned from Bagenholm and other survivors of extreme cold have informed modern medicine to such an extent that cooling patients is emerging as a way to save victims of heart attack, head trauma, stroke and spinal cord injuries.

The idea of protecting patients with cold is not new. Heart surgeons have used cooling since they began operating in the 1950s. Back then, patients were immersed in an ice bath to reduce core body temperature to 25 degrees or lower. This is deep hypothermia, where the circulation is stopped to do the operation. These days, blood is sucked out of the patient, passed through a heat exchanger and pumped back at a colder temperature to induce moderate hypothermia.

The cold simply slows the metabolism. This reduces blood flow for a clearer operating field and lowers the oxygen requirements of the heart and brain, protecting them from damage. The underlying principle of cooling in any medical treatment is that cells need less oxygen at cooler temperatures than at normal body temperature.

"In this unit we routinely cool patients to 32 degrees," the director of cardiothoracic surgery at St Vincent's Clinic, Dr Phillip Spratt, says. "In cases where open heart surgery is very complicated, we would still cool people down to below 20 degrees. You would have about a half an hour for safety as far as the brain is concerned."

When the heart stops beating there is an immediate loss of oxygen-rich blood flow to the brain. Some oxygen is stored in the brain. This provides about a five-minute window for resuscitation when a person at normal body temperature may survive without brain damage.

Cold buys the brain some extra time. Bagenholm's very cold brain needed practically no oxygen after her heart stopped beating.

What recent studies have shown, though, is that even if the brain is cooled after the heart has stopped, people may still have a better chance of surviving without brain damage.

"All of this work is based on the idea that after the primary injury, there is a subsequent 'secondary' injury," says Dr Stephen Bernard, an intensive care physician at the Alfred Hospital in Melbourne, and a pioneer of this research.

Much of the damage done to the brain after the heart has stopped appears to occur when oxygen-rich blood floods back into the cells with resuscitation, and a series of chemical reactions is set off. This causes swelling and inflammation in the brain and reduces oxygen delivery to brain cells.

"So we slow all of this down and reduce all this chemical activity by lowering the body temperature," says Dr Andrew Numa, head of the intensive care unit at Sydney Children's Hospital. Cooling appears to lead to better outcomes for the brain by both reducing inflammation and slowing oxygen demand.

Bernard compared heart-attack patients who were kept at 33 degrees for 12 hours after resuscitation with patients who were not cooled. Of those treated with mild hypothermia, 49 per cent were discharged home or to rehabilitation, compared with 24 per cent treated with standard care. A European study had similar results: 55 per cent for cooled patients, and 39 per cent with favourable outcomes for standard care patients.

"It's an impressive difference," Numa says.

As a result of the cooling studies' findings, the International Liaison Committee on Resuscitation, which includes the Australian Resuscitation Council, advised using therapeutic hypothermia for patients with brain injury after heart attack, but it is still not used in all hospitals.

Questions remain. Which patients should be cooled? What is the best way to cool them? How long should they be cooled and to what temperatures? What are the possible side effects and when is it too late to do any good?

Numa says: "Any situation where the circulation is compromised, I'd probably cool them. In kids it's mostly drowning, in adults, a heart attack on the golf course. The other time is blunt head trauma: car accidents or a kid has fallen off a horse."

For the past two years a trial in which paramedics have cooled more than 400 heart attack victims on their way to hospital has been undertaken. Bernard will present the results later this year. He also plans clinical trials of cooling after head and spinal cord injury, starting next year.

Dr Chris Levi, an associate professor of neurology at the Hunter Medical Research Institute, is working on cooling after severe stroke. "We are also looking at cooling techniques, because it is a challenge to keep humans cool."

Levi is referring to the body's normal response to cooling: shivering. This can cause problems for doctors trying to treat a patient. "All we're really interested in is cooling the brain. It's just hard to cool the brain without the rest of the body," Numa says. "So we usually give them anaesthetic and muscle relaxant so they are comfortable and unable to shiver. Once you do that you've got to take over breathing [artificially]."

At Sydney Children's Hospital patients are placed under cooling blankets that are simply rubberised matresses, with channels of iced water. Ice packs may be placed around the head, neck, torso and limbs. More sophisticated technology has been developed by the US company Medivance. Adhesive pads are stuck to the patient's skin with a gel that simulates immersion in cold water and provides precise temperature control.

Numa says that a new method for cooling without using muscle relaxant is being used in the US. "They put little electrically heated gloves and booties on patients so the fingers and toes are warm, and as far as the brain's concerned, everything's fine."

The upcoming Australian trials will test internal rather than surface cooling techniques, which can also avoid the use of heavy sedation to control shivering. While the mechanisms by which the brain is protected by cooling are still not fully understood by science, this relatively simple intervention could have profound effects for the quality of life of victims of brain trauma.