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Fluids & Electrolytes
Administering 100% oxygen during resuscitation efforts is accepted medical practice. But a startling new study indicates that giving pure oxygen does more harm than good. Although the study was small, researchers say the findings justify review and revision of current guidelines for oxygen delivery, particularly to children.
Using functional magnetic resonance imaging (fMRI), researchers analyzed how the brain responds during oxygen delivery. In one scenario, 14 healthy children (ages 8 to 15) inhaled 100% oxygen through a mouthpiece. Researchers performed fMRI and monitored breathing and heart rates on each child. After waiting 8 minutes, researchers then added 5% carbon dioxide to the mix and repeated the test.
The results were dramatically different. When given pure oxygen, the children's ventilations became more rapid, leading to hypocapnia. This drop in carbon dioxide triggered vasoconstriction, limiting the flow of oxygenated blood to the brain and heart.
The brain responded by triggering the hypothalamus to release a flood of hormones and neurotransmitters into the bloodstream. These harmful chemicals interfered with the heart's ability to pump blood and deliver oxygen.
In contrast, when children inhaled the oxygen/carbon dioxide mix, no hyperactivity by the hypothalamus was observed on fMRI. The increased carbon dioxide concentration was also associated with vasodilation, so more oxygen reached the heart and brain.
The researchers urge health care providers to add carbon dioxide to oxygen, particularly when resuscitating infants or giving oxygen for more than a few minutes. Previous studies with similar findings have already led to policy changes overseas, where many European hospitals use oxygen/carbon dioxide mixtures or even room air during resuscitation efforts.
Macey PM, et al., Hyperoxic brain effects are normalized by addition of CO2, PLoS Medicine, May 22, 2007.
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