In Central Cyanosis there is reduced arterial oxygen saturation which is secondary to marked reduction in oxygen tension in the arterial blood. This is usually manifested when the oxygen saturation of arterial blood is below 80-85%.Involvement of tongue is the key factor that differentiate between central and peripheral cyanosis.
What are the sites to be looked for detection of central cyanosis?
- Cyanosis should be examined in good natural light
- Tongue (mainly the margins as well as the undersurface).
- Inner aspect of lips.
- Mucous membrane of gum. soft palate, cheeks.
- Lower palpebral conjunctiva.
- You should also examine the sites fordetection of peripheral cyanosis
- Congenital cyanotic heart diseases example Fallot's tetralogy.
- Acute pulmonary oedema (due to left ventricular failure) - It is the most common 'cardiac' cause for central cyanosis
- Eisenmenger's syndrome (ASD, VSD or PDA with reversal of shunt due to development of pulmonary hypertension).
- Acute severe asthma.
- Chronic corplmonale and respiratory failure
- Lobar pneumonia.
- Tension pneumothorax.
- Acute laryngeal oedema.
- Pulmonary arteriovenous fistula (congenital, or acquired due to cirrhosis of liver)
- Pulmonary thromboembolism.
High altitude is an important cause of central cyanosis because of the low partial pressure of oxygen. Normally the oxygen saturation of arterial blood is 95% with reduced hemoglobin level only 5%. The oxygen saturation of venous blood is 70% with reduced hemoglobin level only 30%
