Study objective: To assess the effect of nitric oxide inhalation on pulmonary hemodynamics and oxygenation in patients with COPD receiving long-term oxygen therapy (LTOT).
Design: Prospective study.
Setting: ICU of a university medical center.
Patients: A total of 18 (6 female, 12 male) patients with COPD, spontaneously breathing with LTOT.
Interventions: Oxygenation and hemodynamic variables were measured and calculated at an inspired oxygen fraction (FIO2) adjusted to mimic LTOT conditions (control), and then 1 h after each sequential addition of 5, 10, and 20 ppm nitric oxide to the gas mixture. A newly developed device (Pulmonox) provided both the delivery and continuous analysis of nitric oxide and oxidative nitric oxide products.
Measurements and results: There was a significant improvement in oxygenation at 5 ppm nitric oxide (PaO2/FIO2 ratio improved from 244+/-37 to 303+/-59, p<0.05), but no further improvement at higher doses (ceiling effect). There was a dose-dependent improvement in hemodynamic variables that was maximal at 20 ppm nitric oxide (mean pulmonary artery pressure decreased from 29+/-7 to 24+/-5 mm Hg, pulmonary vascular resistance index decreased from 565+/-321 to 392+/-215 dyne x s x cm(-5) x m(-2), and right ventricular ejection fraction improved from 34+/-6 to 39+/-7%, all p<0.05).
Conclusion: Prior studies have demonstrated that inhaled nitric oxide may improve or worsen oxygenation in patients with COPD. Our data show an unequivocal improvement in oxygenation (albeit with a ceiling effect at 5 ppm) and pulmonary hemodynamics (dose dependent) in COPD patients receiving LTOT. Further studies are warranted to examine the usefulness of inhaled nitric oxide during acute exacerbations of COPD, or even the possibility of long-term application in patients receiving LTOT.