cyanosis

cyanosis, bluish coloration of the skin, mucous membranes, and nailbeds, resulting from a lack of oxygenated hemoglobin in the blood. It is a symptom of many disorders, including various pulmonary and heart diseases and many congenital heart defects (see blue baby). Cyanosis that is caused by slowed circulation through peripheral blood vessels results in a bluish tinge only on the cool portions of the body (fingertips, nose, ears). In such cases the capillary blood gives up more than normal amounts of oxygen. Although this type of cyanosis can be caused by reduced cardiac output (e.g., in congestive heart failure), the most common causes are nervous tension and exposure to cold. Another type of cyanosis results from poisoning, either by nitrates in contaminated food or water or by certain chemicals and drugs.

Cyanosis is a blue coloration of the skin and mucous membranes 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 85-90% (1.5g/dl deoxyhemoglobin).

Although human blood is always a shade of red (except in rare cases of hemoglobin-related disease), the optical properties of skin distort the dark red color of deoxygenated blood to make it appear bluish.

The elementary principle behind cyanosis is that deoxygenated hemoglobin is more prone to the optical bluish discoloration, and also produces vasoconstriction that makes it more evident. The scattering of color that produces the blue hue of veins and cyanosis is similar to the process that makes the sky appear blue: some colors are refracted and absorbed more than others. During cyanosis, tissues are uncharacteristically low on oxygen, and therefore tissues that would normally be filled with bright oxygenated blood are instead filled with darker, deoxygenated blood. Darker blood is much more prone to the blue-shifting optical effects, and 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
• Bronchospasm
• 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
• Right to left shunts in heart or great vessels

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)

References

See also

• Blue baby syndrome
• Raynaud's phenomenon

External links

• eMedicine