Methodological aspects of exhaled nitric oxide measurements in infants
Guidelines for the measurement of fractional exhaled nitric oxide (FENO) recommend refraining from lung function tests (LFT) and certain foods and beverages before performing FENOmeasurements, as they may lead to transiently altered FENOlevels. Little is known of such factors in infants. The aim of the present study was to evaluate whether forced expiratory maneuvers, sedation, nasal contamination, and breastfeeding affect FENOvalues in infants. FENOwas measured off-line during tidal breathing by means of a facemask covering nose and mouth. FENOmeasurements were performed in 45 sedated infants (mean age 12.1 months) who underwent LFT because of airway diseases and in 83 unsedated healthy infants (mean age 4.3 months). In infants with airway diseases, no difference was found in FENOvalues before and 5 min after LFT (n = 19 infants, p = 0.7) and FENOvalues before sedation did not differ from FENOvalues during sedation (n = 10 infants, p = 0.2).Oral FENOvalues were significantly lower than mixed (nasal + oral) FENO(n = 42 infants, p < 0.001). FENOvalues before and 5 min after breastfeeding were not different (n = 11 healthy infants, p = 0.57). The short-term reproducibility in healthy infants (n = 54) was satisfactory (intraclass correlation coefficient = 0.94). We conclude that, in infants with airway diseases, LFT prior to FENOmeasurement did not influence FENOvalues and FENOvalues did not change after sedation. Oral FENOvalues were significantly lower than mixed (oral + nasal) FENO, and breastfeeding did not influence FENO. Short-term reproducibility in awake healthy infants was good.