• L Lindberg, G Rydgren, A Larsson, S G Olsson, and L Nordström.
• Department of Anesthesiology and Intensive Care, University Hospital of Lund, Sweden.
• Crit. Care Med. 1997 Jan 1; 25 (1): 190-6.

ObjectiveTo evaluate a system for delivery of inhaled nitric oxide.DesignProspective, laboratory study.SettingEngineering laboratory.SubjectsA standard ventilator (Servo Ventilator 300), supplemented with extra gas modules for nitric oxide delivery.InterventionsTwo ventilator-integrated gas modules, delivering < or = 10 parts per million (ppm) or < or = 100 ppm of nitric oxide, were used in adult and neonatal modes during volume-controlled ventilation. Set nitric oxide concentration and FIO2 were systematically changed and compared with the measured concentration. Short-term mixing was tested in adult, pediatric, and neonatal modes by substituting nitric oxide with CO2, and measuring the delivered concentration by a fast-response CO2 analyzer during five successive respiratory cycles. Long-term mixing was tested with the administration of 25 ppm of nitric oxide for 7 days.Measurements And Main ResultsDelivered concentration of nitric oxide and nitrogen dioxide were simultaneously measured at the Y-place by two methods-chemiluminescence and electro-chemical fuel cells. The maximum absolute difference between set and measured concentrations of nitric oxide in the adult mode was 0.6 ppm at a set concentration of 10 ppm and 2.7 ppm at a set concentration of 100 ppm. In the neonatal mode, the maximal difference was 3.1 ppm at a set concentration of 100 ppm. Nitrogen dioxide concentration increased with increasing concentration of nitric oxide and oxygen to 2.6 ppm (as measured by the chemiluminescence analyzer) and 3.6 ppm (as measured by the electro-chemical fuel cell), at a setting of 100 ppm of nitric oxide with an FIO2 of 0.90 in the neonatal mode (2 L/min). During the short-term test of mixing stability throughout the respiratory cycles, a constant set CO2 concentration varied maximally by +/-6.2% from the set value in the neonatal mode, whereas the variance was by +/-6.5% in pediatric mode, and by +/-8.0% in the adult mode. During the long-term test, nitric oxide concentration varied maximally by +/-2.6% (as measured by the chemiluminescence analyzer) and by +/-2.3% (as measured by the electrochemical fuel cell).ConclusionsAn accurate precision in delivered nitric oxide concentration was achieved during intermittent flow ventilation, and this accuracy was independent of tested ventilator settings. The delivery system administered an almost stable concentration throughout a respiratory cycle and during long-term delivery. If the mixing point is in the inspiratory part of the ventilator, valid measurement of nitric oxide and nitrogen dioxide delivery concentrations are possible. Both techniques for measuring nitric oxide and nitrogen dioxide have drawbacks.

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