Cyanosis – the Blue Baby

Cyanosis is defined as a bluish discolouration of the skin and mucous membranes resulting from an inadequate amount of oxygen in the blood. Cyanosis in infants can be central or peripheral. In some cases, peripheral cyanosis can be normal e.g following cold exposure. Central cyanosis however is always pathological. In the context of CHD, cyanosis is caused by right→left shunting. This causes de-oxygenated blood to mix with oxygenated blood which is then pumped around the body. Cyanotic babies may present collapsed, with blue discoloration of the hands, feet and tongue. It is important to examine carefully as cyanosis can be missed in children with dark skin and is also harder to detect in patients who are anaemic.

Learning bite

5 main CHD lesions causing Cyanosis

  • 1: Truncus Arteriosus – 1 common artery
  • 2: Transposition of the Great arteries – 2 switched arteries
  • 3. Tricuspid Atresia – 3 leaflets of the tricuspid valve are undeveloped
  • 4. Tetralogy of Fallot – 4 defects with one cause
  • 5. TAPVD – 5 words make up the lesion name


congenital heart


Differentials to consider for the cyanosed baby