Low concentrations of inhaled nitric oxide do not improve oxygenation in patients with very severe chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD) is characterized by airway narrowing that is most frequently inhomogeneously distributed. Ventilation/perfusion (V̇/𝑄̇) mismatch may explain much of the hypoxemia in patients with advanced disease. A potential treatment strategy would be to redistribute blood flow to well-ventilated lung regions in order to decrease V̇/𝑄̇ mismatch. It has been suggested that inhaled nitric oxide (iNO) in physiologic concentrations (∼ 100 p.p.b.) could act as a local vasodilating agent in well-ventilated lung regions. To test this, we included 10 volunteer patients with very severe COPD in this study.Methods
NO was mixed with O2 and N2 and administered through a face mask. The partial pressure of inspired oxygen (Pio2) did not change by more than ± 0.5 kPa from the room air value. NO was given in 15-min periods at concentrations of ∼ 0, ∼ 40, ∼ 400, ∼ 4000 and ∼ 40,000 p.p.b. (random order). During each NO exposure, arterial blood gases, methemoglobin and systemic blood pressure were measured every fifth minute.Results
None of the patients reported subjective effects of the different gas mixtures. The partial pressure of oxygen in arterial blood (Pao2) did not change by more than ± 1.2 kPa from the baseline value, and there was no correlation between the change in Pao2 and iNO concentration. No significant changes were found in blood pressure or methemoglobin during iNO.Conclusion
No significant effect of iNO at concentrations up to 40,000 p.p.b. in inspired gas was found on arterial blood gases. This indicates that neither low nor high concentrations of iNO improve oxygenation in patients with very severe COPD.