DEFINITION- Cyanosis is derived from the Greek word “ cyanós (κυανός) ” meaning dark blue 1 . It refers to the bluish discoloration of the skin, nail beds or mucous membranes. While oxygenated hemoglobin is bright red, reduced hemoglobin is dark blue or purple in color and if in sufficient quantity it produces the dusky or blue color of the skin and mucous membranes. According to classical textbook teaching, concentrations of deoxyhemoglobin of about 5 g/dl are necessary before central cyanosis is clinically detectable. This figure has recently been questioned and thought to be a considerable overestimation. (6) Usually, it is associated with oxygen saturation below 85%. Goss et al (6) have reported that central cyanosis can be detected when deoxyhemoglobin levels are 1 -1 g/dl or greater; at concentrations of 1 5 g/dl or more central cyanosis was recognised in all patients. The other factors on which the detection of cyanosis is dependant are amount of Hb pres...