"Several brain areas responded to 100 percent oxygen by kicking the hypothalamus into overdrive," explained Harper. "The hypothalamus overreacted by dumping a massive flood of hormones and neurotransmitters into the bloodstream. These chemicals interfere with the heart's ability to pump blood and deliver oxygen - the opposite effect you want when you're trying to resuscitate someone."
When the children inhaled the carbon dioxide-oxygen mix, the hypothalamus' hyperactivity vanished from the MRI scan.
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"Adding carbon dioxide to the oxygen relaxed the blood vessels, allowed oxygen to reach the heart and brain, calmed the hypothalamus and slowed the release of dangerous chemicals," Macey said.
"Pure oxygen kindles the match that fuels a forest fire of harm to the body," Harper said. "But a little whiff of carbon dioxide makes it all go away."
Based on their findings, the researchers strongly encourage health care providers to add carbon dioxide to oxygen dispensation, especially when resuscitating infants or administering oxygen for more than a few minutes. The new direction could hold particular implications for patients of stroke, heart attack, carbon monoxide poisoning and any long-term oxygen therapy.
"When in doubt about a case, the current medical approach is to increase oxygen levels and wait to see if the patient improves," explained Harper. "But no one has ever scanned patients' brains to examine how they respond to oxygen therapy."
Earlier data on high oxygen's harmful effects have already resulted in policy changes overseas. Instead of using straight oxygen, many European hospitals now resuscitate patients with room air, which contains a mixture of nitrogen, oxygen and carbon dioxide, or with a blend of oxygen and carbon dioxide.
Mary Woo, professor at the UCLA School of Nursing, was a co-author of the study, which was supported by the National Institute of Child Health and Development.
Findings were published in the May 22, 2007 edition of the journal Public Library of Science (PLoS) Medicine.
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