On reddit I saw a snake owner saying what they normally do is kill the prey beforehand with a CO2 chamber
That's a horrible way to die. When you feel like suffocating it's not lack of oxygen but excess carbon dioxide. Breathing in pure CO2 causes instant panic attack on even people with a brain damage making them unable to feel fear. Nitrogen is the gas you want to use - CO2 is among the worst possible choices. Even drowning them would probably be more humane.