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 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 SaO 2 :66% reduced Hb 50g/L

Mean capillary concentration of reduced hemoglobin exceeds 50 g/L. It is the absolute rather than the relative increase.

Normal Polycythemia Anemia g/dl 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.

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

polycythemia patients with marked polycythemia tend to be cyanotic at higher levels of SaO 2 than patients with normal hematocrit( 红 细胞压积 ) values.

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 )

Central cyanosis is caused by decreased SaO2(increased amount of reduced Hb)

Central cyanosis only occurs when the oxygen saturation of arterial blood is less than 85%.

Cause of decreased SaO 2 Parenchymal lung disease( 肺实质病变 ) Right to left cardiac shunt - congenital cyanotic heart disease Decreased P O2 of inspired air - high altitude Hypoventilation( 低通气 )

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 PO 2 and SaO 2

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. Shunting of systemic venous blood into the arterial circuit 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.

Impaired pulmonary function 1. Airway obstruction 2. Pulmonary diseases Right-to-left shunting of blood Tetralogy of Fallot Central Cyanosis

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 FIO 2 and alveolar PO 2 are about 85 and 50 mmHg, respectively, and the SaO 2 is only about 75%. Cyanosis is marked in a further ascent to 3500 m. The reason :the S shape of the Hb-O 2 dissociation curve. Decreased PO2 of inspired air

High O2 affinity Hgb normal 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. Vasoconstriction Low cardiac output Exposure to cold air or water Slowing of blood flow Right heart failure

Peripheral cyanosis Congestive peripheral cyanosis right-side heart failure, constrictive pericarditis, local venous diseases.  slowing of blood flow  abnormally great extraction of O 2 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 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 all causes of central cyanosis may lead to peripheral cyanosis low cardiac output e.g. heart failure

Cyanosis due to abnormal Hb derivatives Central cyanosis may be simulated by methaemoglobulinaemia and sulphaemoglobulinaemia.

Methemoglobinemia 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.

Sulfhemoglobinemia Sulfhemoglobin >5g/L Caused by some drugs or chemicals, Spectroscope is helpful to diagnose

Clinical Classification — Central Type — Peripheral Type — Mixed Type

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 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 Cyanosis Skin temp. Massage or warming Central Warm No change Peripheral Cool Cyanosis fades

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

Sulfhemoglobin Long duration(several months) Spectroscope-630nm

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 PaO 2 tension and SaO 2 Spectroscopic and other examinations of the blood for abnormal types of hemoglobin (critical in the differential diagnosis of cyanosis) Certain features are important in arriving at the cause of cyanosis

History 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 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 Clubbing

Cyanosis + Dyspnea( 呼吸困难 ) Disorders of respiratory or cardiovascular system Cyanosis with mild or no dyspnea Methemoglobinemia Sulfhemoglobinemia: Spectroscopy helpful Cyanosis + clubbing Severe, long duration