What does "cyanosis" mean and what does it indicate?

Cyanosis means a bluish discoloration of the skin and mucous membranes caused by inadequate oxygen in the blood. The term comes from cyano meaning blue and osis meaning condition. Central cyanosis, visible on the lips, tongue, and mucous membranes, indicates severely low blood oxygen levels from respiratory or cardiac causes and requires immediate medical attention. Peripheral cyanosis, seen in the fingers and toes, may result from cold exposure or poor circulation. Cyanosis becomes visible when deoxygenated hemoglobin exceeds approximately five grams per deciliter.