Minimal exhaled nitric oxide production in the lower respiratory tract of healthy children aged 2 to 7 years

BACKGROUND: Exhaled nitric oxide (eNO) is elevated in inflammatory airway conditions, e.g. asthma. We measured eNO levels in normal preschool children for whom there is little data available and in whom the prevalence of asthma is high. SUBJECTS AND METHODS: Fifty children, 2–7 years old, undergoing elective surgery, excluding airway procedures, were recruited. Children with known respiratory disease or acute viral infections were excluded. Gas for eNO measurement was collected in a non-diffusion bag via 1) the mask after inhalation induction of anesthesia, 2) endotreacheal tube (ETT) or laryngeal mask airway (LMA), and 3) during emergence. Measurement was off-line by chemiluminescent analyzer. RESULTS: Mean eNO level by mask was 10.23 ppb (mean value±SD of 8.8–11.1 ppb) after induction and 8.35 ppb (mean value±SD of 5.9–10.8 ppb) on emergence. Mean eNO for the intubated group (n=25) was 0.75 ppb (mean value(SD of 0.4–1 ppb) (P<0.0001 vs mask); mean eNO for the LMA group (n=25) was 2.6 ppb (mean value±SD of 2–3.2 ppb), which differed from the mask (P<0.0001), and from ETT values (P< 0.0001). CONCLUSIONS: Most eNO is produced by the upper airway in healthy pre-school children. The lower airway constitutive eNO production is very low. The LMA does not completely isolate the upper airway and current mask collection techniques allow significant contamination of samples by sino-nasal eNO production in young children.