cyanosis n.
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Cyanosis. Definition. Cyanosis refers to a bluish color of the skin and mucous membranes resulting from an increased quantity of reduced hemoglobin/deoxyhemoglobin ( 脱氧 血红蛋白;还原血红蛋白 ), or abnormal hemoglobin derivatives , in the small blood vessels of those areas. . Mechanism of Cyanosis.

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Cyanosis refers to a bluish color of the skin and mucous membranes resulting from an increased quantity of reduced hemoglobin/deoxyhemoglobin (脱氧血红蛋白;还原血红蛋白), or abnormal hemoglobin derivatives, in the small blood vessels of those areas.

mechanism of cyanosis
Mechanism of Cyanosis
  • Absolute increase of amount of reduced hemoglobin in blood, > 50g/L (capillary)
  • Nonfunctional hemoglobin such as methemoglobin(正铁血红蛋白,高铁血红蛋白)or sulfhemoglobin(硫化血红蛋白) is present in blood.
reduced hemoglobin in blood

desaturation of oxygen

  • Arterial desaturation of oxygen:5%
  • Venous desaturation of oxygen:30%
  • Capillary desaturation of oxygen:average of both
  • SaO2:66% reduced Hb 50g/L
Mean capillary concentration of reduced hemoglobin exceeds 50 g/L. It is the absolute rather than the relativeincrease.

Mechanisms of Cyanosis

Caused by absolute increase of amount of reduced

Hb in blood, usually > 5g/dl (capillary)

The higher the hemoglobin concentration,

The greater tendency toward cyanosis.


Normal Polycythemia Anemia

severe anemia
severe anemia
  • the relative amount of reduced hemoglobin in the venous blood may be very large
  • the absolute quantity of reduced hemoglobin may still be small
  • patients with marked polycythemia tend to be cyanotic at higher levels of SaO2 than patients with normal hematocrit(红细胞压积) values.
clinical classification etiology
Clinical Classification & Etiology
  • True Cyanosis (increased amount of reduced Hb)

— Central Type

— Peripheral Type

— Mixed Type

  • Cyanosis due to abnormal Hb derivatives

— Methemoglobinemia(高铁血红蛋白血症)

— Sulfhemoglobinemia(硫化血红蛋白血症)

cause of decreased sao 2
Cause of decreased SaO2
  • Parenchymal lung disease(肺实质病变)
  • Right to left cardiac shunt - congenital cyanotic heart disease
  • Decreased PO2 of inspired air - high altitude
  • Hypoventilation(低通气)
parenchymal lung disease
Parenchymal lung disease
  • Airway obstruction,pneumonia,massive pulmonary embolism(肺栓塞), pulmonary edema(肺水肿) ,chronic airflow obstruction emphysema (肺气肿)
  • Seriously impaired pulmonary function, through perfusion of unventilated or poorly ventilated areas of the lung or alveolar(肺泡) hypoventilation,resulting in decresed alveolar PO2 and SaO2

Shunting of systemic venous blood into the arterial circuit

  • Congenital cardiac lesion :tetralogy of Fallot (the combination of ventricular septal defect and pulmonary outflow tract obstruction ).
  • Pulmonary arteriovenous fistulae(肺动静脉瘘) :congenital or acquired, solitary or multiple, microscopic or massive.

the presence and severity of cyanosis

depend on the size of the shunt relative to the systemic flow as well as on the Hb-O2 saturation of the venous blood.


Central Cyanosis

Impaired pulmonary function

1. Airway obstruction

2. Pulmonary diseases

Right-to-left shunting

of blood

Tetralogy of Fallot


Decreased PO2 of inspired air

  • At 2500 m the FIO2 is about 120 mmHg, the alveolar PO2 is approximately 80 mmHg, and the SaO2 is nearly normal
  • At 3500 m the FIO2 and alveolar PO2 are about 85 and 50 mmHg, respectively, and the SaO2 is only about 75%.
  • Cyanosis is marked in a further ascent to 3500 m. The reason :the S shape of the Hb-O2 dissociation curve.

High O2 affinity Hgb


Low O2 affinity Hgb

Peripheral cyanosis is due to poor peripheral circulation and increased oxygen consumption in peripheral tissue.

Peripheral Cyanosis

Caused by increased oxygen consumption in peripheral tissue.


Low cardiac output

Exposure to cold air or water

Slowing of blood flow

Right heart failure

peripheral cyanosis
Peripheral cyanosis
  • Congestive peripheral cyanosis

right-side heart failure, constrictive pericarditis, local venous diseases.

  • slowing of blood flow
  • abnormally great extraction of O2 from normally saturated arterial blood.
  • Ischmic peripheral cyanosis.

Ischemic peripheral cyanosis is often seen in severe shock.

Arterial obstruction or constriction.

  • vasoconstriction and diminished peripheral blood flow
mixed cyanosis
Mixed Cyanosis

Clinical differentiation between central and peripheral cyanosis may not always be simple, and in conditions such as cardiogenic shock (心源性休克)with pulmonary edema(肺水肿)there may be a mixture of both types.

possible causes of mixed cyanosis
Possible causesofmixed cyanosis
  • all causes of central cyanosis may lead to peripheral cyanosis
  • low cardiac output e.g. heart failure
cyanosis due to abnormal hb derivatives
Cyanosis due to abnormal Hb derivatives

Central cyanosis may be simulated by methaemoglobulinaemia and sulphaemoglobulinaemia.

  • Hereditary: very rare
  • Acquired:>30g/L in blood

- intake or exposure to some drugs or

chemicals, such as sulfa drugs, nitrite

salt. “ enterogenic cyanosis ”

Spectroscope is helpful to diagnose methemoglobinemia.

  • Sulfhemoglobin >5g/L
  • Caused by some drugs or chemicals,
  • Spectroscope is helpful to diagnose
clinical classification
Clinical Classification

— Central Type

— Peripheral Type

— Mixed Type

possible clinical features include central cyanosis
Possible clinical features include----central cyanosis
  • the warm mucous membranes are blue, for example the tongue, the inside of the lips
  • central cyanosis increases immediately on exercise which is not the case for peripheral cyanosis
  • there is polycythaemia with an abnormally high haemoglobin and haematocrit
  • clubbing is often seen in patients with central cyanosis
possible clinical features include peripheral cyanosis
Possible clinical features include----peripheral cyanosis
  • Cool skin and mucous membrance
  • Site (lower extremities,fingers)
  • Diminish after massage
Note that the absolute discriminating feature between central and peripheral cyanosis is obtained from testing the oxygen saturation of arterial blood.
differentiation of central as opposed to peripheral
Differentiation of central as opposed to peripheral

Cyanosis Skin temp. Massage or warming

Central Warm No change

Peripheral Cool Cyanosis fades

possible clinical features include abnormal hemoglobin
Possible clinical features include----abnormal hemoglobin

Acquired Methemoglobinemia

  • Acutely develop after intaking drugs or chemicals (often severe)
  • Not relieved after oxygen therapy
  • Blood remains brown after being mixed and exposed to air
  • Fades after infusion of methylene blue(亚甲兰)or administration of large dosage of vitamin C
  • Long duration(several months)
  • Spectroscope-630nm
certain features are important in arriving at the cause of cyanosis
Certain features are important in arriving at the cause of cyanosis
  • History (age, gender, family disease history)
  • Clinical differentiation of central as opposed to peripheral cyanosis
  • The presence or absence of clubbing of the digits
  • Determination of PaO2 tension and SaO2
  • Spectroscopic and other examinations of the blood for abnormal types of hemoglobin (critical in the differential diagnosis of cyanosis)
  • particularly the onset (cyanosis present since birth is usually due to congenital heart disease)
  • possible exposure to drugs or chemicals that may produce abnormal types of hemoglobin
lab tests
Lab tests
  • Determination of arterial oxygen saturation
  • oximetric(血氧定量法的)studies
  • physical or radiographic examination ,

echocardiography(超声心动图), right heart catherixation and angiocardiography(心血管造影术)

  • Spectroscope(分光镜检查)


  • The combination of cyanosis and clubbing is frequent in patients with congenital heart disease and right-to-left shunting and is seen occasionally in persons with pulmonary disease such as lung abscess(脓肿) or pulmonary arteriovenous fistulae.
  • In contrast, peripheral cyanosis or acutely developing central cyanosis is not associated with clubbed digits
Cyanosis + Dyspnea(呼吸困难)

Disorders of respiratory or cardiovascular system

  • Cyanosis with mild or no dyspnea


Sulfhemoglobinemia: Spectroscopy helpful

  • Cyanosis + clubbing

Severe, long duration