Paediatric focus – Infants presenting with cyanosis

The differential of cyanosis in children is huge and includes cardiac, circulatory, respiratory and haematological disease, which need to be identified and treated as appropriate.

Infants are a special case in methaemoglobinaemia because innate causes usually present early in life. That does not mean that environmental exposure can be forgotten. A careful history is required. Young children are at higher risk of developing acquired methaemoglobinaemia after an exposure as:

• they have lower levels of cytochrome-b5-reductase
• fetal Hb is more easily oxidised than adult Hb
• the infant gut contains higher levels of organisms that convert dietary nitrates to nitrites
• infants are more susceptible to dehydration and acidosis in diarrhoea and vomiting. It is proposed that acidosis inhibits the reductase pathways.

Suggested approach to the evaluation of cyanosis in neonates and infants

Remember innate Haemoglobin M, G6PD or NADPH-methaemoglobin-reductase deficiency will not respond to Methylene Blue in these infants but acquired causes (e.g. toxin exposure, dietary exposure) and cytochrome-b5-reductase deficiency will.