WordNet

a bluish discoloration of the skin and mucous membranes; a sign that oxygen in the blood is dangerously diminished (as in carbon monoxide poisoning)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/12/24 17:29:10」(JST)

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Cyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface having low oxygen saturation. Based on Lundsgaard and Van Slyke's work,^[1] the onset of cyanosis is classically described as occurring if 5.0 g/dL of deoxyhemoglobin or greater is present.^[2] What is commonly forgotten, however, is that this was based on an "estimate" of capillary saturation based on a mean of arterial versus peripheral venous blood gas measurements.^[3] Since estimation of hypoxia is usually now based either on arterial blood gas measurement, or pulse oximetry, this is probably an overestimate, with evidence that levels of 2.0 g/dL of deoxyhemoglobin may reliably produce cyanosis.^[4] Since, however, the presence of cyanosis is dependent upon there being an absolute quantity of deoxyhemoglobin, the bluish color is more readily apparent in those with high hemoglobin counts than it is with those with anemia. Also the bluer color is more difficult to detect on deeply pigmented skin. When signs of cyanosis first appear, such as on the lips or fingers, intervention should be made within 3–5 minutes because a severe hypoxia or severe circulatory failure may have induced the cyanosis.

The name cyanosis, literally means "the blue disease" or "the blue condition." It is derived from the color cyan, which comes from kyanos, the Greek word for blue.^[5]

Definition

A baby with a heart condition. Note purple nailbeds.

Acute arterial thrombosis of the right leg

Cyanosis is defined as a bluish discoloration, especially of the skin and mucous membranes, due to excessive concentration of deoxyhemoglobin in the blood caused by deoxygenation.

Cyanosis is divided into two main types: Central (around the core, lips, and tongue) and Peripheral (only the extremities or fingers).

Causes

Central cyanosis

Central cyanosis is often due to a circulatory or ventilatory problem that leads to poor blood oxygenation in the lungs. It develops when arterial oxygen saturation drops to ≤85% or ≤75%.

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

Central cyanosis may be due to the following causes:

1. Central nervous system (impairing normal ventilation):

Intracranial hemorrhage
Drug overdose (e.g. Heroin)
Tonic–clonic seizure (e.g. grand mal seizure)

2. Respiratory system:

Pneumonia
Bronchiolitis
Bronchospasm (e.g. Asthma)
Pulmonary Hypertension
Pulmonary embolism
Hypoventilation
Chronic obstructive pulmonary disease, or COPD (emphysema)

3. Cardiovascular diseases:

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

4. Blood:

Methemoglobinemia * Note this causes "spurious" cyanosis, in that, since methemoglobin appears blue,^[6] the patient can appear cyanosed even in the presence of a normal arterial oxygen level.
Polycythaemia
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.

5. Others:

High altitude, cyanosis may develop in ascents to altitudes >2400 m.
Hypothermia
Obstructive sleep apnea

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 in the absence of heart or lung failures. Small blood vessels may be restricted and can be treated by increasing the normal oxygenation level of the blood.

Peripheral cyanosis may be due to the following causes:

All common causes of central cyanosis
Reduced cardiac output (e.g. heart failure, hypovolaemia)
Cold exposure
Arterial obstruction (e.g. peripheral vascular disease, Raynaud phenomenon)
Venous obstruction (e.g. deep vein thrombosis)

Differential cyanosis

Differential cyanosis is the bluish coloration of the lower but not the upper extremity and the head. This is seen in patients with a patent ductus arteriosus. Patients with a large ductus develop progressive pulmonary vascular disease, and pressure overload of the right ventricle occurs. As soon as pulmonary pressure exceeds aortic pressure, shunt reversal (right-to-left shunt) occurs. The upper extremity remains pink because the brachiocephalic trunk, left common carotid trunk and the left subclavian trunk is given off proximal to the PDA.

Approach to diagnosis

Inquire about duration (cyanosis since birth suggests congenital heart disease) and exposures (drugs or chemicals that result in abnormal hemoglobins).
Differentiate central from peripheral cyanosis.
Check for nail clubbing. Combination of clubbing and cyanosis suggests congenital heart disease and occasionally pulmonary disease.
If cyanosis is localized to an extremity evaluate for peripheral vascular obstruction.
Evaluate abnormal hemoglobins by hemoglobin electrophoresis, spectroscopy, and measurement of methemoglobin level.^[7]

References

^ Lundsgaard C, Van Slyke DD. Cyanosis. Medicine. 2(1):1-76, February 1923.
^ Mini Oxford Handbook of Clinical Medicine (7th ed.). p. 56.
^ Cyanosis. Lundsgaard C, Van SD, Abbott ME. Cyanosis. Can Med Assoc J 1923 Aug;13(8):601-4.
^ Goss GA, Hayes JA, Burdon JG. Deoxyhaemoglobin concentrations in the detection of central cyanosis. Thorax 1988 Mar;43(3):212-3.
^ Mosby's Medical, Nursing & Allied Health Dictionary. Mosby-Year Book (4th ed.). 1994. p. 425.
^ Methemoglobin
^ Anthony S. Fauci, et al (2009). Harrison's manual of medicine (17th ed.). New York: McGraw-Hill Medical. ISBN 9780071477437.

External links

Wikimedia Commons has media related to Cyanosis.

Cyanosis definition, types, causes, and general details

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1. 小児におけるチアノーゼの病因および評価 etiology and evaluation of cyanosis in children
2. 新生児におけるチアノーゼの概要 overview of cyanosis in the newborn
3. 新生児におけるチアノーゼの心臓の原因 cardiac causes of cyanosis in the newborn
4. メトヘモグロビン血症の臨床的特徴、診断、および治療 clinical features diagnosis and treatment of methemoglobinemia
5. 幼児および小児における心疾患の疑い：紹介の基準 suspected heart disease in infants and children criteria for referral

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