Central and Peripheral Cyanosis

Cyan means ‘blue’ and the abnormal bluish discoloration of the skin and mucous membranes is referred to as “cyanosis”. It is a pathologic sign, and not a disease by itself. Underlying diseases that increase the deoxygenated hemoglobin to 5.0 g/dl or more leads to cyanosis. Cyanosis can be best appreciated in areas with rich superficial vasculature and thin overlying dermis. These include lips, nose, earlobes, oral cavity, extremities, and tips of fingers and toes. Cyanosis usually becomes evident in hypoxemia, that is, abnormally low concentration of oxygenation (<80-85%) in arterial blood. However, it is not sensitive or a specific indicator of hypoxemia. Since cyanosis is a clinical sign, a proper evaluation is important to determine the etiology of cyanosis. Cyanosis is further classified as central, peripheral, and differential. The bluish discoloration despite adequate oxygenation is sometimes seen due to the ingestion of drugs, toxins, or metals. This is called ‘Pseudocyanosis.’