August 22, 2026

PACES diaries

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Cyanosis

The term “cyanosis” derives from the Greek word “kyanos,” meaning “blue.” The condition has been recognized and documented for centuries, with early descriptions dating back to ancient times. In the 5th century BC, the Greek physician Hippocrates observed and described the bluish discoloration associated with certain respiratory and circulatory disorders.

Over the centuries, as medical knowledge and understanding advanced, the causes and mechanisms behind cyanosis were gradually uncovered. In the 19th century, scientists and clinicians began to better understand the underlying physiological processes responsible for the development of cyanosis.(“CHAPTER 1.: The General Conditions Underlying Cyanosis.,” 1942)

The pathophysiology of cyanosis is related to the presence of deoxygenated hemoglobin in the blood. Cyanosis occurs when the concentration of deoxygenated hemoglobin in the blood exceeds 5 g/dL.(Sasidharan, 2004)

There are two main mechanisms that can lead to cyanosis:

  1. Central Cyanosis:
    • Caused by an imbalance between oxygen supply and demand in the lungs, leading to an increased concentration of deoxygenated hemoglobin in the arterial blood.
    • This can occur due to conditions like congenital heart defects, chronic obstructive pulmonary disease (COPD), or pneumonia that impair the oxygen-carbon dioxide exchange in the lungs.(Pahal & Goyal, 2021)
  1. Peripheral Cyanosis:
  • Caused by poor circulation or reduced blood flow to the extremities, resulting in deoxygenated blood accumulating in the capillaries of the skin and mucous membranes.
  • This can be seen in conditions like Raynaud’s phenomenon, frostbite, or severe vasoconstriction.(Pahal & Goyal, 2021)



Types

Definition

Causes

Central Cyanosis

Results from increased arterial oxygen unsaturation in blood leaving the aorta.

– Ventilation-perfusion mismatch (e.g., pneumonia, chronic bronchitis) – Impaired oxygen transfer (e.g., fibrosing alveolitis) – Right-to-left shunts (e.g., Fallot’s tetralogy) – Absolute excess of desaturated hemoglobin (e.g., primary polycythemia)

Peripheral Cyanosis

Caused by increased utilization of oxygen by tissues, leading to venous oxygen unsaturation.

– Stagnation of blood flow (e.g., Raynaud’s disease, thrombophlebitis) – Cold exposure – Severe mitral stenosis with pulmonary hypertension

Mixed Cyanosis

A combination of both central and peripheral cyanosis.

– Cor pulmonale due to chronic emphysema or lung fibrosis, leading to central cyanosis and right-sided heart failure causing peripheral cyanosis.

Differential Cyanosis

Suggests some parts of the body receive more hypoxic blood than others.

– Cyanosis confined to lower extremities: indicative of pulmonary hypertension with right-to-left shunt (e.g., persistent ductus arteriosus). – Cyanosis confined to upper extremities: suggestive of transposition of the great vessels (e.g., Eisenmenger syndrome). – Cyanosis in upper limbs only can occur in cases of PDA with reversal of shunt and co-existing pre-ductal coarctation of the aorta.

 

Local Cyanosis

Cyanosis confined to an extremity or part of an extremity, particularly the hand or forearm.

Raynaud’s syndrome, scleroderma, peripheral arterial obstruction, thrombophlebitis, phlebothrombosis, varicosities of veins.

Reverse differential cyanosis 

A condition where the arms are more cyanotic than the legs.

Transposition of the great vessels with ventricular septal defect (VSD) and patent ductus arteriosus (PDA).



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