Cyanosis

Definition:

It is the bluish discolouration of skin and mucous membrane due to increased amount

of deoxygenated haemoglobin in the blood. Cyanosis is not seen until the amount of deoxygenated

haemoglobin is .5 gm%.

Types of cyanosis:

It is of 2 types—

1. Peripheral: Due to localized reduction of blood flow on exposure to cold causing capillary

vasoconstriction (lip is blue in cold weather). Also, occurs in reduced cardiac output (heart failure

or shock). Tongue is spared in peripheral cyanosis. 

Causes are:

• • Exposure to severe cold, frostbite.
• • Raynaud’s phenomenon.
• • Heart failure.
• • Shock and peripheral circulatory failure.
• • Deep vein thrombosis.
• • Cryoglobulinaemia.

2. Central: Either due to imperfect oxygenation of blood in lung or admixture of venous and

arterial blood. It is evident when O2 saturation falls below 80 to 85%. Best site to see is tongue.

Causes are:

Respiratory: There is defect in oxygenation of blood in the lungs:

• • Chronic obstructive pulmonary disease (COPD).
• • Severe pneumonia.
• • Tension pneumothorax.
• • Massive lung collapse.
• • Acute severe bronchial asthma.
• • Massive pulmonary embolism.
• • Pulmonary infarction.
• • Diffuse parenchymal lung disease (DPLD).
• • Adult respiratory distress syndrome.
• • Respiratory failure due to any cause.

Cardiac:

• • Cyanotic congenital heart disease: Fallot’s tetralogy, transposition of great vessels.
• • Shunt anomaly (reversal of shunt, right-to-left shunt called Eisenmenger syndrome), causes are:
• atrial septal defect, ventricular septal defect, patent ductus arteriosus.
• • Acute left ventricular failure.
• • Cardiogenic shock.

Others:

• High altitude (physiological).

• Polycythaemia.