Nitric oxide improves pulmonary vascular resistance but not oxygenation in ARDS, heart transplant, and pulmonary hypertension

Introduction

We study the effects of inhaled NO on oxygenation (P/F ratio), and pulmonary vascular resistance (PVR) in 15 patients with ARDS, cardiac transplant and pulmonary hypertension for a minimum of 48 h.

Methods

Data were collected prior to NO therapy, 24 and 48 h after NO was initiated. For each subject PVR and P/F ratio for the three time periods were plotted against the corresponding dose of inhaled NO (ppm). Using these plots linear regression analysis was performed. The slopes of the regression lines (b) were averaged for each of the three groups and a student's t-test was performed on each group's data to identify significant correlation.

Results

The PVR was found to be decreased (b = -5.38), (P < 0.01) in all three groups. NO increased the P/F ratio (b = 1.69), but this was not statistically significant. When considering the groups individually, the ARDS group (n = 3) had on average a decrease in PVR (b = -7.02), and improvement of P/F ratio (b = 4.71). This group received an average concentration of NO of 22.7 ppm for an average of 10 days. The cardiac transplant group (n = 6) showed improvement in the PVR (b = 5.59) with almost no effect on the P/F ratio (b = 0.345). This group received an average of NO of 34.8 ppm for an average of 6 days. The pulmonary hypertension group (n = 6) revealed a significant reduction in the PVR (b = -3.81) with a P < 0.025, and there was increase in the P/F ratio (b = 1.528). This group received an average concentration of NO of 41.4 ppm for an average of 5.5 days.

Conclusion

Inhaled NO had a greater effect on PVR than on P/F ratio. In the cardiac transplant group, NO decreased the PVR but had little effect on oxygenation (P/F). In the pulmonary hypertension group, NO decreased the PVR but not improvement in P/F ratio. In this study, the only significant effect of NO was on the PVR in patients considered as a whole and in the pulmonary hypertension subgroup. Patients with ARDS had the least benefit of NO therapy. We attribute this lack of response in oxygenation to severe underlying pulmonary condition as well as other comorbid illnesses.