Cyanosis is the bluish tinge of skin and mucous
membranes seen when there is too little oxygen bound to hemoglobin in the blood.
If generalized it may due to inadequate oxygen reaching the blood or failure
of the blood circulation; this may be chronic or acute, the latter often
needing early treatment or resuscitation. If it is only at the extremities,
it indicates slow blood flow due to vasoconstriction.