Table 4.09. Cyanosis.

"A bluish discoloration, applied especially to such discoloration of skin, mucous membranes and nail beds due to excessive concentration of 'reduced' hemoglobin in the blood".
Caused by 4 or more g/dL of deoxygenated Hb in arterial blood, regardless of total hemoglobin conc.; arterial O2 saturation below 85%.
Types -
- Central or Shunt Cyanosis - caused by some forms of congenital heart disease (>25% shunt), and right and left heart failure.
- Peripheral Cyanosis - caused by extensive O₂ extraction at capillary level, extreme peripheral constriction (Raynaud's).
Accompanying conditions - polycythemia, clubbing of fingers and toes (especially when cyanosis marked), cerebral thrombosis, etc.