Cyanosis of the extremities in newborns gradually increases with age and activity. Cyanosis is generalized, and if combined with arteriovenous catheterization at the same time, differential cyanosis occurs, with heavier cyanosis in the upper branches than in the lower extremities. It is the most common manifestation of cyanotic congenital heart disease in the neonatal period, and complete transposition of the great arteries is the most common, with an incidence of 0.2‰~0.3‰. The incidence is 11.4 times higher in diabetic mothers than in normal mothers, and the incidence is higher in pregnant women who have used hormones and anticonvulsant drugs in early pregnancy. 1, temporary cyanosis (1) physiological cyanosis: normal newborns can sometimes show cyanosis within 5 min after birth, due to the arterial duct and foramen ovale have not yet closed, still maintain the right-to-left shunt, the lung has not yet fully expanded, pulmonary ventilation function is not perfect and poor perfusion of the surrounding skin. 5 min after the changes in the circulatory system has been completed arteriovenous blood flow completely separate, the lips and nail bed become pink, but sometimes the skin is still mildly cyanotic. However, sometimes the skin is still mildly cyanotic, especially after exposure to cold environment, the distal limb local blood flow slows down and reduces hemoglobin, so although PaO2 is not low limb is still obviously cyanotic, called peripheral cyanosis, the cyanosis can be reduced or disappeared after strengthening insulation. (2) Transient cyanosis: normal newborns may occasionally appear cyanosis when they cry hard because the pressure in the thoracic cavity increases when they cry, making the pressure in the right atrium rise above the pressure in the left atrium, forming a right-to-left shunt through the foramen ovale, and this transient cyanosis disappears immediately after the crying stops. 2, central cyanosis: caused by cardiopulmonary disease to reduce arterial SO2 and PaO2, according to the cause can be divided into pulmonary and cardiogenic. (1) pulmonary cyanosis: such as neonatal asphyxia respiratory congenital malformations, such as Pierre-Robin syndrome postnasal obstruction pulmonary hyaline membrane disease pulmonary expansion insufficiency, pneumonia pneumonia, swelling gas, chest congenital diaphragmatic hernia, congenital pulmonary arteriovenous, fistula sustained fetal circulation, etc. (2) cardiogenic cyanosis: congenital heart disease with right-to-left shunt is more common in the neonatal period: tetralogy of Fallot, large vessel displacement, left heart dysplasia, syndromic pulmonary vein ectasia, tricuspid atresia of the common reflux arterial stem and severe pulmonary stenosis. 3, peripheral cyanosis system: due to the slow blood flow through the peripheral circulation capillaries, tissue oxygen consumption increases and leads to an increase in the amount of local reduced hemoglobin, but the arterial SO2 and PaO2 are normal. (1) Systemic diseases: slow blood flow in the body circulation in heart failure, reduced cardiac output in shock, reduced blood supply in the peripheral circulation, stagnant blood flow in the capillaries, increased blood viscosity in erythrocytosis, and reduced cardiac output in hypothermia in sclerosis can slow blood flow and cause cyanosis. (2) Local blood flow disorders: bruising can occur when the first dewlap is pressured during delivery, such as the face and buttocks. In addition, cyanosis can also occur in the extremities of newborns under physiological conditions.