Methaemoglobinaemia risk factors with inhaled nitric oxide therapy in newborn infants

Background: Inhaled nitric oxide (iNO), commonly used for hypoxic neonates, may react with haemoglobin to form methaemoglobin (MetHb). MetHb monitoring during iNO therapy has been questioned since low doses of iNO are used. Aim: To evaluate the incidence of and identify risk factors associated with elevated MetHb in neonates treated with iNO. Methods: Neonates who were treated with iNO and had at least one MetHb measurement were included. Demographic characteristics and methods of iNO administration (dosage, duration) at the time of each MetHb measurement were analysed. Results: Four hundred and fifty‐two MetHb measurements from 81 premature and 82 term and near‐term infants were analysed. MetHb was above 5% in one‐term infant, and between 2.5–5% in 16 infants. A higher maximum dose of iNO (22.7 vs 17.7 p.p.m.), but not gestational age, was a significant risk factor for elevated MetHb. Significantly higher oxygen levels (75.5% vs 51.7%) were associated with higher MetHb in term infants. Preterm infants had no risk for high MetHb when iNO was kept below 8 p.p.m. These data suggest the possibility of limiting blood withdrawal when low doses iNO are used. Conclusion: High MetHb is exceptional in neonates treated with low dose iNO. Associated risk factors are related to high iNO dose and the simultaneous use of high concentrations of oxygen.