Carbon dioxide - by what mechanism is it poisonous?

William G. Ewald wmgeoewald at
Mon Jul 28 12:56:10 EST 1997

> I am interested in finding out the mechanism by which CO2 is poisonous.
> My understanding is that Carbon MONOXIDE(CO) competes with oxygen for binding
> to haemoglobin, and whereas CO2 and O2 have relatively low affinities, the
> affinity that haemoglobin has for carbon monoxide is very high - the effect
> being that CO stays bound, whereas O2 and CO2 are able to exchange.
> So, given this information (if it is correct), it would seem that CO2 does not
>  have its toxic effect by acting through high-affinity binding to haemoglobin,
> preventing O2 binding.
> I used to think that CO2 is not poisonous, and that it only kills when it
> displaces the oxygen in a container.  I have since been told that this is NOT
> the case and that it IS toxic.
> I would appreciate enlightenment on this subject.
> If you can help, an email reply would be the preferred method.
> Many thanks.

    Carbon dioxide is an asphyxiant at sufficiently high levels; it will
cause an increase in breathing rate at a level you would get by putting
a paper bag over your head.

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