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) 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 in a cohort of ventilator-dependent children with a tracheostomy and to explore the relationship between the peak F concentration (F 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 peak and F 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 peak, exhaled NO output (equal to the F peak × minute ventilation), and pulmonary NO excretion (exhaled NO output/weight) were calculated and correlated with the respiratory severity score.

RESULTS

The median F peak was 2.69 ppb, and the median F plateau was 1.57 ppb. The coefficients of repeatability between the 2 consecutive measurements for F peak and F 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, < .001) for F peak and 0.991 (95% CI 0.982-0.996, < .001) for F plateau. We found that the F peak was directly correlated with minute ventilation, but we did not find a direct relationship between the F peak concentration, exhaled NO output, or pulmonary NO excretion and respiratory severity score.

CONCLUSIONS

F 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 peak concentration from the lower airway is low and influenced by minute ventilation in children receiving mechanical ventilation.