The safety of a nitric oxide inhalation system with high frequency oscillatory ventilation

Nitric oxide (NO) inhalation and high frequency oscillatory ventilation (HFOV) has been indicated in infants with severe respiratory failure. The purpose of the present study was to evaluate the safety of an NO inhalation system with HFOV in terms of nitrogen dioxide (NO₂) production. The NO inhalation system consisted of a high frequency oscillatory ventilator, a neonatal circuit and a test lung. The NO concentration was changed from 0 to 19 p.p.m. At each level of NO, the oxygen (O₂) concentration was changed from 21 to 100%. The NO and NO₂ concentrations were measured with a chemiluminescence analyzer using a molybdenum converter. The NO₂ concentration was increased when either the O₂ or the NO concentration was increased. The interposition of the endotracheal tubes increased NO₂ concentrations at 4 p.p.m. NO. The high stroke volume and high mean airway pressure produced a significant increase in NO₂ production at 4 p.p.m. NO. The increase in NO₂ production was prevented by placing a one-way valve at the joint of the NO gas line to the inspired limb. It was concluded that the NO inhalation system with HFOV can be safely used when a one-way valve is placed at the joint of the NO gas line to the inspired limb and when inhaled NO is at a relatively low concentration.