"Peter Duniho" wrote in message
Blue fingernails are one of the *last* signs of hypoxia. Unless you had a
CO leak or something like that, you'd never have blue fingernails at modest
altitudes, even though using oxygen will significantly improve your state of
mind.

Actually, if you have CO in the cockpit, you won't get cyanosis either, dang
insidous thing about CO poisoning is that it leaves the tissues nice and red.