Cyanosis
Cyanosis is the blue-purple discoloration of the skin and mucous membranes caused by elevated blood concentration of deoxygenated hemoglobin, of at least 4 g/dL.
Central cyanosis results from desaturated blood flowing from the aorta. The vermillion of the lips (the area lipstick goes) is a fairly good approximation, but the inside of the mouth or eyelids are the best. In children, cyanosis around the mouth can be a normal response.
Peripheral cyanosis results from peripheral vasoconstriction (occurring in the arterioles).
This corresonds to an arterial O2 saturation of 85% or less in someone with normal oxygen levels.
If someone is anemic, someone will need to have a much lower oxygen saturation.
(In children at least,) cyanosis does not necessarily lead to.
Hypercyanotic (Tet) spells
Differential cyanosis
lower cyanosis - occurs with coarctation of the aorta and a patent ductus arteriosus. Differential upper cyanosis can occur with coarctation and transposition of the great vessels.