A Novel Method of Measuring Fractional Exhaled Nitric Oxide in Tracheostomized Ventilator-Dependent Children

BACKGROUND: The lower airway concentration of fractional exhaled nitric oxide (F-ENO) is unknown in children with chronic lung disease of infancy who have tracheostomy for long-term mechanical ventilation. We aimed to evaluate an online method of measuring F-ENO in a cohort of ventilator-dependent children with a tracheostomy and to explore the relationship between the peak F-ENO concentration (F-ENO peak) and the degree of respiratory support using the respiratory severity score. METHODS: We conducted a prospective cross-sectional study in 31 subjects who were receiving long-term respiratory support through a tracheostomy. We measured the F-ENO peak and F-ENO plateau concentration from the tip of the tracheostomy tube using a nitric oxide analyzer in subjects during a quiet state while being mechanically ventilated. We obtained 2 consecutive 2-min duration measurements from each subject. The F-ENO peak, exhaled NO output (equal to the F-ENO peak x minute ventilation), and pulmonary NO excretion (exhaled NO output/weight) were calculated and correlated with the respiratory severity score. RESULTS: The median F-ENO peak was 2.69 ppb, and the median F-ENO plateau was 1.57 ppb. The coefficients of repeatability between the 2 consecutive measurements for F-ENO peak and F-ENO plateau were 0.74 and 0.59, respectively. The intraclass coefficient between subjects within the cohort was 0.988 (95% CI 0.975-0.994, P < .001) for F-ENO peak and 0.991 (95% CI 0.982-0.996, P < .001) for F-ENO plateau. We found that the F-ENO peak was directly correlated with minute ventilation, but we did not find a direct relationship between the F-ENO peak concentration, exhaled NO output, or pulmonary NO excretion and respiratory severity score. CONCLUSIONS: F-ENO peak and plateau concentration can be measured online easily with a high degree of reliability and repeatability in infants and young children with a tracheostomy. F-ENO peak concentration from the lower airway is low and influenced by minute ventilation in children receiving mechanical ventilation.