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• Caused by abnormal elevations of hemoglobin or hemoglobin derivatives:
  • Reduced hemoglobin >5 g/dL
  • Methemoglobin >1.5 g/dL
  • Sulfhemoglobin >0.5 g/dL
• The amount of oxyhemoglobin does not affect the blood’s color.
• Cyanosis is more common in patients with polycythemia.
• Cyanosis is less common in patients with anemia.
• Methemoglobinemia cyanosis presents with normal PO₂ and chocolate-colored blood.

Central cyanosis/decreased saturation:

• Impaired pulmonary function:
  • Hypoventilation:
    • Pneumonia
    • Chronic obstructive pulmonary disease
    • Pulmonary edema
  • Ventilation/perfusion mismatch:
    • Asthma
    • Pulmonary embolus
  • Diffusion problems:
    • Interstitial lung disease
    • Anatomic shunts
  • Congenital cardiac causes:
    • Transposition
    • Tetralogy
  • Pulmonary arteriovenous fistula:
    • Hereditary hemorrhagic telangiectasia
  • High-altitude related, with decreased atmospheric pressure at 16,000 feet
• Low-oxygen affinity hemoglobin mutants ...

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