Oxygen – too much of a good thing ?

We’ve known for sometime that high inspired oxygen fractions (>0.8) are associated with atelechasis (and decruitment / shunt) and lung injury and suspected that hyperoxia also leads to the generation of toxic oxygen free radicals, which may have deleterious effects in other pathologies. A recent paper adds to this story;

Association between arterial hypoxia following resuscitation from cardiac arrest and In Hopsital mortality. Hope, J et al. JAMA. 2010;303(21):2165-2171 (doi:10.1001/jama.2010.707).

This paper has been appraised by a colleague, Paul Townsley, and you can download his presentation from the blue box on the right. Although the methodology has some potential flaws (which is probably inevitable), the paper provides evidence of definite harm of hyperoxia in ischemic brain injury.

Of course, there is an alternative weight of evidence of the harm associated with even short periods of desaturation in traumatic brain injury (and presumably also brain injury from poor perfusion). How to square this circle? The devil as always is in the detail. Controlling hyperoxia is probably important, but whether the benefits of avoiding hyperoxia outweigh the additional risk of periods of desaturation, or how often those periods occur within patient populations, is unknown. There is sufficient evidence to warrant a carefully designed RCT in the post resuscitation phase, (and maybe also in ARDS while we’re at it).

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