[Azrael3000]

You cant avoid co2 build-up, you can only slow it down, main factor here is relaxation. Particularly your brain needs loads of o2, so if you can keep that calm it helps a lot. Obviously a slow metabolism helps as well, so before big static performances fasting is common.

And regarding co2 tolerance, it is a training effect. With training you can withstand much higher levels of co2 without resulting in panic

[cenamus]

And co2 build up isn't even that dangerous, just really uncomfortable. Lack of co2 (from hyperventilating) actually inhibits oxygen uptake and causes dizzyness (up to passing out) that way