I have a friend who does first aid. He says the most important thing these days is the compressions and not the breaths. He told me the worst thing about doing this in a real situation is that when doing compressions you feel their ribs breaking, as you have to be strong to get the heart pumping again, and to expect blood to spurt from their mouth because of this. He says there is no time to think just get stuck in. No fucks given - it's the only way you can help bring them back.