Unintended inhalation of nitric oxide by contamination of compressed air -Physiologic effects and interference with intended nitric oxide inhalationin acute lung injury

Background: Compressed air from a hospital's central gas supply may contain nitric oxide as a result of air pollution. Inhaled nitric oxide may increa se arterial oxygen tension and decrease pulmonary vascular resistance in pa tients with acute lung injury and acute respiratory distress syndrome. Ther efore, the authors wanted to determine whether unintentional nitric oxide i nhalation by contamination of compressed air influences arterial oxygen ten sion and pulmonary vascular resistance and interferes with the therapeutic use of nitric oxide, Methods: Nitric oxide concentrations in the compressed air of a university hospital were measured continuously by chemiluminescence during two periods (4 and 2 weeks). The effects of unintended nitric oxide inhalation on arte rial oxygen tension (n = 15) and on pulmonary vascular resistance (n = 9) w ere measured in patients with acute lung injury and acute respiratory distr ess syndrome by changing the source of compressed air of the ventilator fro m the hospital's central gas supply to a nitric oxide-free gas tank contain ing compressed air. In five of these patients, the effects of an additional inhalation of 5 ppm nitric oxide were evaluated. Results: During working days, compressed air of the hospital's central gas supply contained clinically effective nitric ox ide concentrations (> 80 pa rts per billion) during 40% of the time. Change to gas tank-supplied nitric oxide-free compressed air decreased the arterial oxygen tension by 10% and increased pulmonary vascular resistance by 13%. The addition of 5 ppm nitr ic oxide had a minimal effect on arterial oxygen tension and pulmonary vasc ular resistance when added to hospital-supplied compressed air but improved both when added to tank-supplied compressed air. Conclusions: Unintended inhalation of nitric oxide increases arterial oxyge n tension and decreases pulmonary vascular resistance in patients with acut e lung injury and acute respiratory distress syndrome. The unintended nitri c oxide inhalation interferes with the therapeutic use of nitric oxide.