Cyanosis

Bluish discoloration of skin and mucous membranes, resulting from increased amount of reduced hemoglobin or hemoglobin derivatives in the capillary blood.
Most marked in lips, nails beds, ears and malar eminence.
Causes-
A. central cyanosis

• Due to decreased arterial saturation

1. Cardiac causes-

• fallot's tetralogy
• Eisenmenger's syndrome
• congestive cardiac failure

    2.  Pulmonary causes-

• chronic bronchitis
• interstitial lung disease
• pulmonary arteriovenous fistula

   3.  High altitude

   4.   Cirrhosis of liver

• Due to abnormal hemobglobin derivatives

1. Methemoglobinemia
2. sulphahemoglobinemia

B. Peripheral cyanosis

1. due to diminished blood flow resulting from decreased cardiac output

• Mitral stenosis
• caongestive cardiac failure
• shock

     2.   due to local vasoconstriction

• cold exposure
• raynaud's disease
• peripheral vascular disease