Cyanosis is the clinical description of the bluish discolouration of the skin and mucous membranes that corresponds to greater than 5 g/dl of deoxygenated haemoglobin in the blood. Mild degrees may not be observed and a saturation monitor should be used to confirm normality. Look for central cyanosis in the tongue and mucous membranes.

Cyanosis (oxygen saturation less than 94%) may be due to cardiac disease, respiratory disease, metabolic disease or sepsis.


Be mindful of where the saturation probe is positioned. It should be in the right hand to pick up cyanotic heart disease (pre-ductal saturation). If only the feet are blue (post-ductal saturation), then it could be due to right to left shunt at the duct in coarctation of the aorta.

Assessing cyanosis

When assessing whether cyanosis may be present, remember the following points:

  • Peripheral cyanosis is normal in the first few days of life and cyanosis only whilst crying is rarely significant
  • Polycythaemia or methaemoglobinaemia may cause a baby to appear blue, but these are not associated with structural cardiac defects
  • Anaemia and dark skin tones make it more difficult to detect cyanosis
  • Some babies with cyanotic heart disease may appear fairly pink due to the high affinity for oxygen of fetal haemoglobin

Learning Bite

Cyanosis with little or no respiratory distress and lack of radiographic evidence of lung disease suggests underlying congenital heart disease.


A hyperoxia test is useful in distinguishing between cardiac and pulmonary causes of desaturation. With the infant inhaling 100% FiO2, the arterial PaO2does not increase significantly if the cause is cardiac. In a neonate (under 4 weeks), it is always worth considering the use of a prostaglandin infusion. Oxygen is not helpful in the treatment of cyanotic CHD: indeed, one of the ways to make the diagnosis is to show that there is little improvement in saturations when oxygen is administered. Then an echocardiogram should be performed. Surgical procedure performed based on the lesion.