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Heat stroke? Forget the ice, says study

When it comes to cooling a heat stroke victim, forget the ice and immerse them in temperate water, new research suggests.

The research, by Associate Professor Nigel Taylor of the University of Wollongong and colleagues, appears in the journal Medicine and Science in Sports and Exercise.

"Cooling in temperate water took only marginally longer than that in cold water, and one cannot imagine that the 45 [second] cooling difference would have any meaningful physiological or clinical implications," Taylor and colleagues write.

From fun runners and cricketers, miners and soldiers, working out in the heat, especially in heavy protective clothing, can lead to dangerous overheating.

Sports scientist Dr Matt Brearley of the Northern Territory Institute of Sport says once a person's core temperature reaches 39.5°C to 40.5°C they get hyperthermia.

"Most of the bodily processes will start to break down," he says.

Brearley says people lose their ability to regulate blood flow properly and can even stop sweating. This means they store more heat at the time when they most need to dissipate it.

And a person's failure to control blood pressure generally leads to collapse, says Brearley.

"Then they're in grave danger because they're actually threatening their life," he says.

The medical response to hyperthermia is to cool the body as quickly as possible by immersing the patient in cold water, of about 14°C.

But, say Taylor and colleagues, this may not always be practical.

"Access to ice or cold water may be limited in hot climates," they write.

They also say that some experts suggest sudden cold-water immersion may actually shut down the blood supply to the skin and make it harder for heat to dissipate from the body.

Experiment

Taylor and colleagues wondered whether temperate water might be as effective in cooling people down.

They compared how long it took to cool an overheated person in temperate water as opposed to air, and cold water.

Their trial involved eight males who were heated to a temperature of 39.5°C (as measured by a sensor inserted into the oesophagus).

The men exercised in 36°C and 50% relative humidity while wearing a suit with 40°C hot water pumping through it.

"That's very uncomfortable," says Brearley.

The researchers then compared how long it took the men to cool down in 20-22°C air, 14°C water and 26°C water. They found little difference between the effects of cold and temperate water.

Taylor and colleagues assume that the temperate water has a less drastic affect on the skin's blood supply than cold water, and this compensates for the fact that it is not as cold.

Brearley agrees it would be more practical to use temperate water to cool people with hyperthermia, but he thinks it's too early to recommend changes for heat stroke treatment.

"I'd like to see some more data on this," he says. "It's a starting point for further investigation."

He says such findings may be particularly relevant to the survival of people suffering hyperthermia in remote areas, including miners and soldiers.

"Water has such a great cooling power compared to air," says Brearley.

The researchers received defence funding for the new study.