how is mouth to mouth (CPR) beneficial if you’re blowing carbon dioxide into their lungs?

Question

See title

In: Biology

Answer 1

Your inhales are about 20% O2, and your exhales are about 15% O2. That 15% O2 is still worth it.

Edit for more exact numbers: atmosphere (the general air) is listed at 21% oxygen, and most studies of exhales is at 16% oxygen. And it seems that what *really* matters is how much pressure the oxygen has, so as long as there’s at least 5% of oxygen at sea level pressures it will still be useful to have in your lungs (this is why space suits can be filled with pure oxygen, which is normally unhealthy, but at about 20% of the pressure). I was reading the [Breathing wiki page](https://en.wikipedia.org/wiki/Breathing).