Life Science Encyclopedia

Cyanosis is a bluish coloration of the skin due to the presence of deoxygenated hemoglobin in blood vessels near the skin surface. It occurs when the oxygen saturation of arterial blood falls below 85%.

The elementary principle behind cyanosis is that deoxygenated hemoglobin produces the bluish discoloration, and also produces vasoconstriction that makes it more evident. Thus oxygen deficiency - hypoxia - leads to blue discoloration of the lips and other mucous membranes.

The name is derived from the color cyan, the Greek word for blue.

Types

Cyanosis can occur in the fingers, including underneath the fingernails, as well as other extremities (called peripheral cyanosis), or in the lips and tongue (central cyanosis).

Central cyanosis

Central cyanosis is often due to a circulatory or ventilatory problem that leads to poorer blood oxygenation in the lungs or greater oxygen extraction due to slowing down of blood circulation in the skin's blood vessels.

Acute cyanosis can be a result of asphyxiation or choking, and is one of the surest signs that respiration is being blocked.

Common causes of central cyanosis

• Abnormal hemoglobin levels
• Congenital heart disease
• Heart failure
• Heart valve disease
• High altitude
• Hypothermia
• Hypoventilation
• Lung disease
• Myocardial infarction
• Polycythaemia
• Pulmonary embolism
• COPD (Emphysema and Chronic Bronchitis)
• Asthma
• Methemoglobinemia
• Tetralogy of Fallot

Peripheral cyanosis

Peripheral cyanosis is the blue tint in fingers or extremities, due to inadequate circulation. The blood reaching the extremities is not oxygen rich and when viewed through the skin a combination of factors can lead to the appearance of a blue color. All factors contributing to central cyanosis can also cause peripheral symptoms to appear, however peripheral cyanosis can be observed without there being heart or lung failures. Small blood vessels may be restricted and can be treated by increasing the normal oxygenation level of the blood.

Common causes of peripheral cyanosis

• All common causes of central cyanosis (see above)
• Arterial obstruction
• Cold exposure (due to vasoconstriction)
• Raynaud's phenomenon (vasoconstriction)
• Reduced cardiac output (e.g. heart failure, hypovolaemia)
• Vasoconstriction
• Venous obstruction (e.g. deep vein thrombosis)

See also

• Blue baby syndrome
• Raynaud's phenomenon