As far as I know, CO2 itself can cause you to blackout. As the PaCO2 goes over 90mmHg, you enter CO2 narcosis; once you enter CO2 narcosis, you have around 2 minutes before you suffer from 'narcolepsy', or spontaneous falling asleep/loss of consciousness.
The most striking example of this was during the Duke study when subjects would inhale pure oxygen, then hold their breath and bike on a stationary bike. Their oxygen levels were monitored during the test. Some subjects couldn't resist the urge to breathe, but those who could first entered CO2 narcosis, then blacked out, despite having totally safe levels of oxygen dure to the inhalation of pure oxygen.
The question this brings up is one that me and my friends have been struggling with for ages: is CO2 narcosis caused by low blood acidity in general, or is it the CO2 itself? i.e. could lactic acidosis cause narcosis?
This is very important for me since I nearly blacked out from CO2 narcosis during a deep dive last year.
Because blackout from CO2 happens at depth, a safety freediver on the surface cannot help you....
Eric Fattah
BC, Canada
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