Blue baby syndrome can refer to conditions that cause cyanosis, or blueness of the skin, in babies as a result of low oxygen levels in the blood. This term has traditionally been applied to cyanosis as a result of:Cyanotic heart disease, which is a category of congenital heart defect that results in low levels of oxygen in the blood. This can be caused by either reduced blood flow to the lungs or mixing of oxygenated and deoxygenated blood. Methemoglobinemia, which is a disease defined by high levels of methemoglobin in the blood. Increased levels of methemoglobin prevent oxygen from being released into the tissues and result in hypoxemia.
Although these are the most common causes of cyanosis, there are other potential factors that can cause a blue tint to a baby's skin or mucous membranes. These factors include hypoventilation, perfusion or ventilation differences in the lungs, and poor cardiac output of oxygenated blood, among others. The blue baby syndrome or cyanosis occurs when absolute amount of deoxygenated hemoglobin >3g/dL which is typically reflected with an O2 saturation of <85%.
Both of these conditions cause cyanosis, or a bluish discoloration of skin or mucous membranes. Normally, oxygenated blood appears red and deoxygenated blood has more of a blue appearance. In babies with low levels of oxygen or mixing of oxygenated and deoxygenated blood, the blood can have a blue or purple color, causing cyanosis.