Cyanosis is a clinical manifestation of desaturation of arterial and capillary blood and may indicate haemodynamic instability

Pathophysiology

peripheral cyanosis, for example of the feet and hands, is very common in the first 24 hours of life and may occur when the child is crying or unwell from any cause - thought to represent venous congestion caused by immature control of vascular tone in neonates (acrocyanosis)

Central cyanosis can be recognised clinically when the concentration of reduced haemoglobin in the blood exceeds 3-5g/dl

• Note a child with cyanosis may present with normal O2 sats as the haemoglobin levels can affect how desaturated they have to be before they become cyanotic

Causes of increased deoxygenated haemoglobin:

1. Hypoventilation
2. VQ mismatch
3. diffusion abnormalities
4. Right to left shunt
5. Inadequate oxygen transport (Hb)

Differential diagnosis

Causes of cyanotic congenital heart disease

• tetralogy of Fallot (TOF)
• transposition of the great arteries (TGA)
• tricuspid atresia
• Truncus arteriosus
• Hypoplastic left heart syndrome