<unk>  is defined as bluish discoloration of skin and mucous membrane due to decreased oxygenation of tissue. Approximately 2% of oxygen dissolved in plasma and 98% is carried by hemoglobin. In central<unk> , there is decreased oxygen saturation (less than 85%) or abnormal or nonfunctional hemoglobin, depending on whether reduced hemoglobin or desaturated hemoglobin exceeds 5 g/dl. Common signs of  central<unk>  include the tongue and conjunctiva appearing blue in color and the extremities becoming warm with rapid capillary filling. In peripheral<unk> , the oxygen saturation is normal but there is inadequate delivery of oxygen to tissue or increased oxygen extraction by tissue due to peripheral vasoconstriction. In peripheral<unk>  extremities are cyanotic, pale, cool but tongue and conjunctiva are pinkish. All causes of central<unk>  may lead to peripheral<unk> . In the presence of anemia and severe hypoxemia,<unk>  may not be apparent due to fewer levels of reduced hemoglobin. Conversely, in polycythemia and mild hypoxemia,<unk>  may be easily apparent due to an increased level of reduced hemoglobin.
Cyanosis
Polycythemia
Acrocyanosis
Myxedema
Dry skin
Retinopathy
Dry eyes
Color blindness