Cyanosis

Cyanosis

190px A baby with a heart condition. Note purple nailbeds.
ICD-10	R23.0
ICD-9	782.5

Cyanosis is a blue coloration of the skin and mucous membranes due to the presence of greater than, or equal to, 2.5 g/dL of deoxygenated hemoglobin in blood vessels near the skin surface.

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, which comes from kyanous, the Greek word for blue.

Cyanosis is an abnormal blue discoloration of the skin and mucous membranes and requires an absolute concentration of deoxygenated haemoglobin of > 5 g/dL. It is actually easier to appreciate in those with high hemoglobin than those with anemia. It can be difficult to detect in patients with deeply pigmented skin. When signs of cyanosis first appear, intervention must be made within 3–5 minutes.

Definition

Cyanosis is divided in to two main types: central (around the core and lips) and peripheral (only the extremities are affected).

Differential diagnosis

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 poor 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.

Causes

1. Central Nervous System:

• Intracranial hemorrhage
• Cerebral anoxia
• Drug overdose (e.g. Heroin)

2. Respiratory System:

• Bronchiolitis
• Bronchospasm (e.g. Asthma)
• Lung disease
• Pulmonary embolism
• Hypoventilation
• COPD (emphysema and chronic bronchitis)

3.Cardiac Disorders:

• Congenital heart disease (e.g. Tetralogy of Fallot, Right to left shunts in heart or great vessels)
• Heart failure
• Heart valve disease
• Myocardial infarction

4.Blood:

• Methemoglobinemia
• Polycythaemia

5.Others:

• High altitude
• Hypothermia
• Congenital cyanosis (HbM Boston) arises from a mutation in the α-codon which results in a change of primary sequence, H --> Y. Tyrosine stabilises the Fe(III) form (oxyhaemoglobin) creating a permanent T-state of Hb.

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.

Causes

• All common causes of central cyanosis
• 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
• Blue Fugates

External links

• Cyanosis definition, types, causes, and general details
• eMedicine

ar:زرقة (طب) zh:發紺