CENTRAL CYANOSIS

1. DECREASED ATMOSPHERIC O2 — high altitude
2. IMPAIRED PULMONARY FUNCTION
   • Alveolar hypoventilation (e.g. bronchoconstriction in COPD)
   • Uneven relationships between pulmonary ventilation and perfusion i.e. perfusion of hypoventilated alveoli; PQ mismatch (e.g. pulm. embolus)
   • Impaired oxygen diffusion
3. ANATOMIC SHUNTS
   • Certain types of congenital heart disease
   • Pulmonary arteriovenous fistulas
   • Multiple small intrapulmonary shunts
4. HEMOGLOBIN ABNORMALITIES
   • Methemoglobinemia—hereditary, acquired
   • Sulfhemoglobinema—acquired
   • Carboxyhemoglobinemia (not true cyanosis)

PERIPHERAL CYANOSIS

1. Reduced cardiac output (Heart failure)
2. Cold exposure (e.g. Raynaud disease)
3. Redistribution of blood flow from extremities
4. Arterial obstruction; PVD
5. Venous obstruction; DVT

Thanks to Harrison’s Electronic Textbook of Internal Medicine (16th edition; PalmOS version) for some of the information presented above.