Cyanosis is a bluish discoloration of the nails, skin and/or mucosa due to increased amount of reduced hemoglobin (more than 5 mg%) in capillary blood.
Types of Cyanosis
3. Cyanosis due to abnormal pigments
In an adult, on an average, there is 15 gm% of hemoglobin, 95% of which is saturated with oxygen and only 5% i.e. 0.75 gm% is reduced. Hence, in capillaries, a mean of the two i.e. only 2-3 gm% is reduced hemoglobin and the color of the skin and mucous membranes is pink.
When the amount of reduced hemoglobin exceeds 5 gm% in the capillaries, the blood appears dark, giving the tissues a bluish hue.
Central cyanosis is seen in areas of high circulation e.g. palate, tongue, inner sides of the lips and conjunctiva.
Peripheral cyanosis occurs due to slowing of blood which allows more time for removal of oxygen by the tissues, so that cyanosis is visible on the tip of nose, ear lobule, tip of finger, nail-bed and cheek.
In mixed cyanosis there is both arterial hypoxemia and sluggish circulation.
- Congenital, cyanotic heart disease: Fallot’s tetrad, Eisenmenger’s complex etc.
- Congestive cardiac failure.
- Chronic obstructive lung disease.
- Collapse and fibrosis of lung.
- Marked pulmonary destruction due to any cause.
- High altitude due to low partial pressure of oxygen.
- Cold (local vasoconstriction)
- Increased viscosity of blood
A. Acute left ventricular failure
B. Mitral stenosis (left atrial failure and peripheral vasoconstriction).
Cyanosis Due to Abnormal Pigments
Normal hemoglobin has iron in ferrous form. In methemoglobinemia, iron is in the ferric form designated as MHb. Several substances like nitrate ingestion (well water), sulfonamide or aniline dyes oxidize Hb to MHb, but this is immediately reduced back to Hb by methemoglobin reductase I or diaphorase I. If there is deficiency of diaphorase I MHb circulates in blood causing cyanosis.
Sulfhemoglobin (SHb) is an abnormal sulphur containing substance which is not normally present but is formed by toxic action of drugs and chemicals like sulphonamides, phenacetin, and acetanilide. SHb forms an irreversible change in the Hb pigment that has no capacity to carry oxygen and causes cyanosis.
- Only of lower limbs- Patent ductus arteriosus (PDA) with reversal of shunt.
- Only of upper limbs- PDA with reversal of shunt in a transposition of great vessels.
- Cyanosis of left upper and both lower limbs- PDA with reversal of shunt and pre-ductal coarctation of aorta.
Condtions Where Cyanosis Does Not Occur
- In severe anemia where hemoglobin is less than 5 gm%, even if all the hemoglobin is reduced in the capillaries, it will be less than the critical level of 5 gm% and cyanosis does not occur.
- In carbon monoxide poisoning, carboxy-hemoglobin prevents reduction of oxyhemoglobin and the former has a cherry red color. Hence there is no cyanosis.
Investigations in Cyanosis
- Arterial Blood Gases
- Complete Blood Count – Hemoglobin level is increased with chronic cyanosis. White cell count is increased in pneumonia and pulmonary embolism.
- ECG to rule out cardiac abnormalitie
- Chest xray to rule out pneumonia, pulmonary infarction, cardiac failure.
- Ventilation-perfusion scan or pulmonary angiography to rule out pulmonary embolism.
- Echocardiography to look for cardiac defects.
- Hemoglobin spectroscopy to look for methaemoglobinaemia, sulfhaemoglobinaemia.
- Digital subtraction angiography to rule out acute arterial occlusion.
- Duplex Doppler or venography to find acute venous occlusion.
Management of Cyanosis
Cyanosis is a sign, manifestation of an underlying cause. So the underlying cause should be treated. Oxygen for patients in hypoxia is indicated.
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