The Truth About... Hypothermia

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HOW DID he survive? That was the question many people asked following the news earlier this week that 13-month-old Liam Evans had spent three nights alone, without food and water, on a Welsh hillside. His grandfather had taken him for a car drive, but died after a crash on the Thursday night, which left the car invisible from the road. Liam was discovered when a boy heard his cries on Sunday morning. In between, nobody, including Liam himself, knew where he was.

One early suggestion for his remarkable survival was that his body, unable to generate enough warmth, had shut itself down in order to conserve energy. Such hypothermia - a fall in the temperature of the body's core, normally 37C (98.6F) - does lead to a remarkable reduction in energy needs. In fact, our core temperature falls a little when we go to sleep at night. But this is not usually the prelude to hypothermia.

Clinically, that condition begins when the core temperature falls to 35C. The associated changes are surprising: "The heart beats more slowly, at less than half of its normal rate," explains Ken Collins, a retired hospital doctor who is acknowledged as an expert on hypothermia. "The breathing rate slows, too; if you see a true hypothermic, you can hardly tell that they're breathing at all."

Thus, people who appear dead on arrival at hospital after being in freezing conditions can, with the right means of revival (to raise the core temperature before the skin temperature), turn out to be perfectly healthy. Emergency physicians have a saying to sum up this fact: "They're not dead until they're warm and dead."

In true hypothermia, everything slows down, including the activity of the tissues and brain. The lowest ever recorded core temperature in a survivor is 15.2C, in a 23-day-old infant.

But while hypothermia can in fact help survival, it is dangerous, and scores of people die from it every year. Dr Collins says: "Below 35C there are great risks because it's more likely that the heart will slow down so much that it stops, or goes into fibrillation [irregular contractions]. Then you can have ventricular fibrillation, which can kill."

Nobody knows exactly what combination of outside temperatures and internal body energy stores is required to trigger hypothermia. But the evidence suggests that Liam did not become hypothermic. It is summer, and the temperature drop at night, though substantial, was probably not enough to induce hypothermia.

One persuasive argument for this is that Liam's rescuer was alerted by the baby's cries. "If he had been in deep hypothermia, he wouldn't have been conscious, and couldn't cry," says Dr Collins. "I think he was a reasonably healthy child, which meant he had a margin of about four days. That's how long they can last without food or water." On that basis, Liam was rescued just 24 hours from death.