Variation of inspired nitric oxide and nitrogen dioxide concentrations during mechanical ventilation

Inhaled Nitric oxide is a selective and potent pulmonary vasodilator with minimal influence on systemic vascular resistance. Due to these properties NO becomes widespread treatment for pulmonary hypertension of different etiologies. However, during inhalation via inspiratory limb of breathing circuit NO reacts with oxygen, producing nitrogen dioxide (NO2) which is known to be a toxic agent. Therefore, the exact measurements of NO and NO2 concentrations is very important during NO therapy, as was previously described by several authors. The aim of this study was to measure NO and NO2 concentrations at different sites of inspiratory limb of breathing circuit. Significant changes were found between different sites of circuit: Highest NO and lowest NO2 concentrations were detected at the distal points of circuit. We conclude, that NO delivery system should be connected with inspiratory limb of breathing circuit as distally as possible, to minimize contact of NO air with oxygen and to achieve maximal NO and minimal NO2 concentrations during inspiration.