4 | NewScientist | 18 December 2010

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ONE clinical examination should be enough to establish whether a person has no brain activity. A second test is not only unnecessary, but also makes organ donation less likely.

So says Eelco Wijdicks of the Mayo Clinic in Rochester, Minnesota, whose study is challenging guidelines for diagnosing brain death in certain US states. New York, for example, recommends using two clinical exams 6 hours apart.

Wijdicks and colleagues reviewed the cases of 1311 people diagnosed as brain-dead at 100 New York hospitals. Each person had two examinations with an average time interval of 19 hours.

No brain function returned, and viable organ donors fell from 57 to 45 per cent as the time between the exams increased. Organ donation was no longer

Dead is dead an option in about 12 per cent of the cases because of cardiac arrests between or after the exams. During this time, family opposition to donation increased from 23 to 36 per cent.

The researchers think that refusal to allow donation could be a result of the stress and sense of uncertainty that families experience when having to wait for multiple diagnoses.

The American Academy of Neurology has updated its guidelines on brain death, developed in 1995, to recommend only one examination.

Lice off the hookARE fish farms bad for wild Pacific salmon populations? The long-running debate just got a little murkier.

Wild populations have been in decline for decades, and the sea louse, a parasite common on farmed salmon, has taken much of the blame. The louse can spread from the mesh pens of salmon farms and infect juvenile wild salmon as they head seaward. Earlier studies showed that wild salmon that encounter fish farms are less likely to survive

than those in farmless areas.However, those studies did not

include counts of sea lice on the farmed fish. When Gary Marty of the University of California, Davis, and his colleagues looked at that aspect for the Broughton Archipelago of western Canada, they found that salmon survival was not lower in years when the juveniles passed by louse-infested farms. This, they say, suggests that something other than sea lice must be reducing survival rates (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1009573108).

Stagnant scienceHUMAN odours that repel mosquitoes and a herbal remedy to combat malaria are among the ideas being developed in Africa that need commercial support.

“The fundamental issue is not money, it’s culture, and the need for scientists to refocus away from simply publishing results,” says Peter Singer, director of the McLaughlin-Rotman Center for Global Health in Toronto, Canada, who carried out a

–Fighting for food–

–Nets save lives–

No Arctic tipping point?IT WILL be little consolation to hungry polar bears in northern Manitoba, Canada, who have had to wait weeks longer than usual for sea ice to form on Hudson Bay, but their habitat is not irreversibly doomed. It could be saved – if we cut greenhouse gas emissions.

Polar bears only hunt from ice platforms at sea. The worry has been that the Arctic will hit a tipping point beyond which there will be no ice in summer, causing the bears to starve. That’s because the dwindling ice reflects less heat into space, causing it to warm up faster and melt away.

Steven Amstrup of Polar Bears International in Bozeman, Montana, and colleagues ran a climate model for 2000 to 2100. In the “business as usual” run, greenhouse gas emissions continued to increase and the ice

shrank, with a rapid collapse in the 2020s. But in a second run, in which greenhouse gas levels stopped rising after 2020, the sea ice shrank until 2020 then recovered, suggesting no tipping point had been passed.

The team then plugged their sea ice figures into a model of polar bear populations. In the business-as-usual scenario, the bear population fell by two-thirds by 2050, but in the recovery scenario the population declined only slightly (Nature, DOI: 10.1038/nature09653). “By mitigating our emissions, we could substantially improve things for polar bears,” Amstrup says.

Tim Lenton of the University of East Anglia in Norwich, UK, cautions that there may be a more distant tipping point for year-round ice.

“Waiting for multiple tests of brain death made families less likely to agree to organ donation”

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