Cyanosis: Understanding Skin Discoloration Due to Low Oxygen

Cyanosis is a bluish-purple discoloration of skin/mucous membranes resulting from increased deoxygenated hemoglobin (≥5 g/dL) in capillary blood. It is a clinical sign, not a disease.

Types

• Central cyanosis: Lips, tongue, oral mucosa. Indicates arterial hypoxemia (SaO₂ < 85%, PaO₂ < 60 mmHg). Causes: cardiac (R→L shunt, heart failure), pulmonary (pneumonia, PE, ARDS), high altitude.
• Peripheral cyanosis: Fingers, toes, nose, earlobes. Caused by vasoconstriction/slowed flow → increased O₂ extraction. Seen in shock, cold exposure, heart failure, PVD. Central cyanosis absent.
• Differential cyanosis: Lower body only (PDA with pulmonary hypertension) or upper body only (reversed PDA, aortic interruption).

Assessment

• Check in natural light (avoid fluorescent).
• Compare mucosal vs. peripheral sites.
• Correlate with pulse oximetry (SpO₂) and ABG.
• Note: Anemia masks cyanosis (less Hb); polycythemia exaggerates it.

Causes by System

• Respiratory: Pneumonia, asthma, COPD, PE, pneumothorax.
• Cardiac: Cyanotic congenital heart disease (Tetralogy of Fallot), acute heart failure.
• Hematologic: Methemoglobinemia (chocolate cyanosis, SpO₂ ~85% despite 100% O₂), sulfhemoglobinemia.
• Toxic: Carbon monoxide (cherry red, not blue), cyanide.

Central cyanosis is a medical emergency requiring immediate oxygenation and diagnosis.