Dear Editor,

We read with interest the review on exhaled breath measures of inflammation by Harrison et al.[1] We agree that there is a need to develop and standardise methods for the collection of exhaled breath markers as part of clinical monitoring of neonates on respiratory support. A major limitation we encountered with collecting exhaled breath condensates (EBC) using a method we published earlier was that hydrogen peroxide concentrations were not significantly different between condensates from babies and "dummy" controls.[2] This could be a result of signal dilution of small expired gas volumes from infants by relatively large bias flow, mixture of gases and airway humidification in the ventilator/continuous positive airway pressure circuits.[2]

Nevertheless, their article prompted us to analyse if there were any trends in exhaled hydrogen peroxide concentrations from 44 ventilated infants with respiratory distress syndrome (RDS) (median gestation and birthweight of 28 weeks and 1025 g respectively) in relation to the development of chronic lung disease (CLD) (oxygen requirement at 36 weeks post-menstrual age). The median hydrogen peroxide concentration in infants who developed CLD was 0.30 uM (interquartile range 0.21 - 0.46 uM) compared with 0.21 uM (interquartile range 0.16 - 0.37 uM) of those with resolved RDS (p=0.042). There was no significant correlation between fractional inspired oxygen and hydrogen peroxide concentrations.

We emphasise that these results are still inconclusive due to deficiencies in our collecting system. Further evaluation is required using more refined methods of collection. In this respect, Hitka et al attempted to capture only expired gases from ventilated preterm infants using a double valve outlet system.[3] This looks promising, although validation of the method with various modes of ventilation and settings, and with a larger and more diverse patient group is necessary before exhaled hydrogen peroxide is considered for monitoring of ventilated neonates at risk for CLD.

FC Cheah Department of Paediatrics, Faculty of Medicine, Universiti Kebangsaan Malaysia, Bandar Tun Razak, 56000 Kuala Lumpur, Malaysia

BA Darlow, CC Winterbourn Departments of Paediatrics and Pathology, Christchurch School of Medicine and Health Sciences, Christchurch, New Zealand

References

1. Harrison CM, Andersen CC. Exhaled breath measures of inflammation: are they useful in neonatal chronic lung disease? Arch Dis Child Fetal Neonatal Ed. 2005;90:F6-10.

2. Cheah FC, Darlow BA, Winterbourn CC. Problems associated with collecting breath condensate for the measurement of exhaled hydrogen peroxide from neonates on respiratory support. Biol Neonate. 2003;84:338- 341.

3. Hitka P, Cerny M, Vizek M, Wilhelm J, Zoban P. Assessment of exhaled gases in ventilated preterm infants. Physiol Res. 2004;53:561-564.