Whether low levels would work for ER patients with hypoxia remains unclear
WEDNESDAY, Jan. 7 (HealthDay News) -- Going to the world's most elevated natural laboratory, Mount Everest, British researchers have found that the established medical rules about the amount of oxygen needed by a body under stress might be wrong.
"Some people can tolerate extremely low levels of oxygen, much lower than we expected," said Dr. Michael P.W. Grocott, from University College London and lead author of a report in the Jan. 8 New England Journal of Medicine.
His team determined their findings on hypoxia, which is low levels of oxygen, from measurements made on 10 climbers as they went up and down Everest, whose peak of more than 29,000 feet above sea level is the highest point on earth.
The report is the first to come from a large-scale project "specifically designed to understand the differences between people and how they react to hypoxia," Grocott said. Those differences are difficult to measure in ordinary hospital laboratories, but the Everest project provided a way for "measurement of unusual people in a strange place," he added.
The researchers, from the Center for Altitude, Space and Extreme Environment Medicine at the University College London's Institute of Human Health and Performance, wanted to make blood measurements at the very peak of Everest, but the weather did not allow that. Instead, samples were taken at the highest level possible, at an altitude of about 27,559 feet. The blood oxygen readings at that level "are, to our knowledge, among the lowest ever documented in humans," the researchers wrote.
"I don't expect patients to survive in oxygen levels that we saw in these subjects," Grocott said. Yet all of them "were functioning perfectly ably," he added.
The Everest finding could lead to a change in the treatment of the hypoxia often seen in people in emergency rooms, like those suffering heart attacks.
The first rule now in such cases is to keep blood oxygen levels high by whatever means possible, Grocott noted. "But mechanical ventilation can be harmful," he said. "It can cause inflammation in the lungs. The gentler you are, the less damage you do to the lungs."
The data from the Everest study is not nearly enough to be put to use medically, Grocott said. "We are not proposing a change in clinical practice," he said. But he added that it was enough to spur a proposal for a randomized clinical trial of less aggressive oxygen-supplying treatments in some cases.
"We are currently seeking funding for such a trial in the United Kingdom," he said. "We would do the trial in people at lowest risk to hypoxia, not to those with heart attack and stroke. It would be in younger people with no vascular [blood vessel] disease, traumatically injured patients with injured lungs."
But what is seen in Everest climbers might not be true in the emergency room, said Dr. Norberto C. Gonzalez, professor of molecular and integrative physiology at the University of Kansas, who has done research on hypoxia.
The climbers in the study had spent substantial amounts of time at high altitudes, Gonzalez said. "These people are acclimatized," he said. "If you and I were exposed to this level of oxygen, we couldn't take it."
While he expressed marvel at the measurements, "as low in oxygen as you can get and still be alive," Gonzalez expressed doubt that the findings seen in experienced climbers could be extended to ordinary hospital treatment.
"I'm not so sure that you can extrapolate what happens to a healthy individual who is exposed to an extreme to someone who has many problems," he said.
What hypoxia can do to the brain is described by the U.S. National Institute of Neurological Disorders and Stroke.
SOURCES: Michael P. W. Grocott, M.D., Center for Altitude, Space and Extreme Environment Medicine, Institute of Human Health and Performance, University College London, and senior lecturer in intensive care, University College London, England; Norberto C. Gonzalez, M.D., professor of molecular and integrative physiology, University of Kansas Medical Center, Kansas City, Kan.; Jan. 8, 2009, New England Journal of Medicine
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