Effects of oxygen and nitric oxide in oxygen on pulmonary arterial pressures of children with congenital cardiac defects

Inhaled nitric oxide is a specific pulmonary vasodilator. This study was undertaken to assess the effect on pulmonary arterial pressure of administering 100% oxygen compared with nitric oxide in oxygen. Thirteen mechanically ventilated children undergoing routine cardiac catheterization for the investigation of congenital heart disease were studied. Pulmonary arterial pressures were measured during inhalation of 30% oxygen (baseline), 100% oxygen, and nitric oxide (40 parts per million) in oxygen. In addition, in six children the pulmonary/systemic blood flow ratio and pulmonary vascular resistance were calculated using oxygen content, an assumed value for oxygen uptake, and the Fick principle. Results were compared using analysis of variance and the Wilcoxon signed-rank test. Pulmonary arterial pressure decreased from a mean value of 29.5 mmHg (SD 15.1) to 25.6 mmHg (SD 9.3), p= 0.048, after increasing the inspired oxygen fraction from 0.3 to 1.0. The addition of nitric oxide caused a further reduction to 22.9 mmHg (SD 7.9), p= 0.0001. There was no change in systemic arterial pressure or heart rate during the study period, but a small increase occurred in the mean methemoglobin level (1.1% to 1.3%) p= 0.039. Changes in the pulmonary/systemic blood flow ratio and pulmonary vascular resistance (n= 6) were not significant. Nitric oxide in oxygen appears to be a more potent pulmonary vasodilator than oxygen alone in pediatric patients with congenital cardiac defects.