Cyanosis overview and Definition

 Cyanosis refers to the bluish discoloration of the skin and the mucous membrane.

It occurs due to the inadequate supply of oxygen to the tissues.

Sometimes cold temperatures can cause blood vessel narrowing and lead to temporarily blue-tinged skin. Warming or massaging the blue areas should return normal blood flow and colour to the skin.


In order for circulating blood to appear blue, it requires an elevated amount of blue pigment to accumulate. Central cyanosis is generally of greater concern, as it requires reduced arterial oxygen saturation (PaO2)  or abnormal derivatives of hemoglobin can be present(methemoglobin or silfhemoglobin) and it is the delayed finding in the course of illness.  The increased amount of deoxygenated hemoglobin is due to an increased amount of venous admixture (due to vasodilatory effects on the venous plexi) or by reduced  arterial oxygen tension in the capillaries.

 In central cyanosis, either SaO2 is reduced or abnormal (nonfunctional) hemoglobin is present, which is why central structures and mucosae are affected; this is in contrast to peripheral cyanosis, where there is a normal SaO2 but increased extraction of oxygen in the setting of peripheral vasoconstriction and thus, decreased peripheral blood flow. As McGee1 astutely notes, historically there has been (and exists still in the teaching of medical students today) great confusion about the actual levels of deoxyhemoglobin required to produce clinically apparent cyanosis. This is because many clinicians erroneously equate arterial levels of deoxyhemoglobin with capillary levels—and it is the capillary levels, not the arterial ones, that yield the blue color we observe. Another important point is that it is the absolute, not relative, quantity of deoxygenated hemoglobin that matters; this means that for a given patient, the level of SaO2 at which cyanosis becomes apparent depends on their total hemoglobin concentration. Because of this, severely anemic patients with marked arterial desaturation might not be cyanosed, yet polycythemic patients develop obvious cyanosis at much higher SaO2  associated conditions

Clinical signs & symptoms

  • Chest muscles pulling in with every breath or flaring nostrils with breathing
  • Difficulty breathing or rapid breathing
  • Fussiness or irritability
  • Grunting
  • Limpness or lethargy
  • Poor feeding or sleeping
  • Sitting very still with shoulders hunched

Differential Diagnosis

Bluish skin is usually a sign of something serious. If normal color does not return when the skin is rubbed or warmed it is vital to seek the medical help.

Arterial Blood Gas Test: It measures the acidity and levels of carbon dioxide and oxygen in the blood.

Electrocardiogram: It is taken to completely the rule out the prevalence of cardiac abnormalities.

Chest X ray: It is taken to rule out the conditions like pneumonia, pulmonary infarction and cardiac failure.

Ventilation Perfusion Scan or Pulmonary Angiography: It is taken to rule out the pulmonary causes.

Echocardiography: It is used to look for the presence of any cardiac defects.

Haemoglobin Spectroscopy: The spectroscopy checks for the methemoglobinemia or sulfhemoglobinemia.

Digital Subtraction Angiography: It is done to completely rule out conditions like acute arterial occlusion.

Doppler or venography:

A duplex doppler or Venography can detect the prevalence of acute venous occlusion.


Follow healthy lifestyle

Do physical activities

Avoid cold environments when not able to adapt

Cessation of smoking