Addition of Nitric Oxide to Oxygen Improves Cardiopulmonary Function in Patients With Severe COPD: Pulmonary vascular resistance
However, although NO led to a consistent and dose-dependent decrease in pulmonary vascular resistance, the mean Pa02 increased significantly at 40 ppm only, and then only from 57±3 to 60±3 mm Hg (p<0.01). In fact, in 4 of the 13 patients, Pa02 actually declined. In a study on inhaled NO at 15 ppm in a similar group of patients, Moinard et al demonstrated a consistent decrease in pulmonary vascular resistance proportional to the baseline elevation in MPAP, but no change in mean Pa02. Finally, Barbera et al found that, compared with room air breathing, NO at 40 ppm actually worsened mean Pa02, from 56 ±2 to 53±2 mm Hg (p-0.014). Arterial oxygenation improved in 3 of the 13 patients with advanced COPD that they studied, but deteriorated in the remainder. Using a multiple inert-gas elimination technique, they demonstrated that NO worsened V/Q matching, with increased perfusion to poorly ventilated lung units so buy antibiotics online. Because breathing 100% oxygen had a similar effect, they suggested that NO reverses hypoxic pulmonary vasoconstriction. In a recent study by Yoshida et al of 10 spontaneously breathing COPD patients not receiving LTOT, the authors found that the combined inhalation of NO and oxygen led to a significant decrease in MPAP and increase in oxygenation.
Our study differed from those done previously, in that NO was added to LTOT in a dose-ranging fashion. We found an unequivocal improvement in both oxygenation and pulmonary hemodynamics, but there was a differential response to increasing NO concentration (Fig 1), as has been described in patients with ARDS. The maximum enhancement of oxygenation occurred at the lowest NO concentration (5 ppm), demonstrating a ceiling effect. It has been shown that NO—even in the parts per billion range—can substantially improve oxygenation. Especially in a subgroup of COPD patients where there is only mild or even no pulmonary hypertension, low concentrations of inhaled NO may lead to the desired effect of improved oxygenation. Therefore, we think that the effects of small dosages of NO on oxygenation should be studied in future trials.
Figure 1. Pulmonary vascular resistance and oxygenation responses to NO. All values are mean±SEM; n=18; asterisk: p<0.05 compared with control values; dagger: p<0.050, 10 ppm vs 5 ppm NO; section mark: p<0.05, 20 ppm vs 10 ppm NO. Dose response of PVRI (dyne • s * cm • irT2) and Pa02/FIo2 (oxygenation index) to different NO concentrations showing a ceiling effect for oxygenation at low concentrations of NO.