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>When teaching on a BSAC Oxygen Administration course we tell our students >to expect a transient worsening of symptons to a casualty shortly after >starting to administer 100% O2. This is due to two reasons. Firslty, if >there is a lodged bubble some of the oxygen in solution will diffuse into >the nitrogen bubble. Secondly, the body reacts to the higher partial pressure >of O2 and reduces the blood flow due to vasoconstriction. This can be read >in the BSAC Safety and Rescue manual. This may be a stupid question but I was brought up to believe that the only stupid question is one that goes unasked... Given that the patient will be breathing *some* gas at 1 ata, why would O2 diffuse into the nitrogen bubble any more than additional nitrogen (if they were only breathing air)??? The way that I see it, if you're breathing pure O2 then the PP N2 in the lungs and bloodstream should go down (faster than by breathing air, which would have a PP N2 of .79) causing an increased rate of N2 offgassing. Eventually, the N2 bubble will diffuse back into solution because of a low PP N2 in the surrounding tissues. The issue will be whether this happens soon enough to prevent tissue damage. If my logic is flawed I'm sure I will be corrected... -Carl-
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