The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

EVALUATION OF FOUR INHALED NITRIC OXIDE THERAPY ANALYZERS USING KNOWN CONCENTRATIONS OF NITROGEN DIOXIDE

Peter Betit RRT, Barry Grenier RRT, John Thompson RRT. Respiratory Care Department, Children's Hospital, Boston, MA.

We previously evaluated 4 analyzers that are used to monitor nitric oxide (NO) and nitrogen dioxide (NO_2) concentrations during inhaled NO therapy. NO readings were accurate in all 4 analyzers but NO_2 readings differed between analyzers. NO_2 readings obtained from two side-stream (SS) analyzers were significantly higher than readings from two main-stream (MS) analyzers (p < .001). We speculated that the sample technique accounted for these differences. A second study was conducted to verify the accuracy of these analyzers using known concentrations of NO_2. Three electrochemical (EC) models; Pulmonox II (PMX), Bedfont NOxBOX (BFX) and Drager 190 NO_2 (DRG), and one chemiluminescence (CL) device; Thermoenvironmental 42M (THM) were studied. The BFX and the 42H are SS and the PMX and DRG are MS. All four analyzers were calibrated according to the manufacturers' specifications. The EC devices were calibrated at 25 cmH_2O pressure. NO_2 from a 12.5 ppm source tank was titrated into the inspiratory limb of an infant ventilator (VIP Bird). NO_2 concentrations were determined from the equation: NO_{2-CALC}=NO_2 Source[cdot]NO_2 VVdot / NO_2 VVdot + Ventilator VVdot. NO_2 VVdot and ventilator VVdot were verified and 5 NO_2 concentrations ranging from 1 to 8 ppm were used. The ventilator, connected to a test lung, was set in the time cycled IMV mode at a PiP/PEEP of 30/5 cmH_2O, rate 25, Ti 0.6 secs and an FiO_2 of .21. All exhausted gases were scavenged. Each analyzer was studied independently and NO_2 measurements were recorded after five minutes of stabilization. The study was repeated three times and mean values used for analysis. Ventilator settings were observed and remained stable throughout the study. NO_2 measurements were compared to NO_{2-CALC}. There was a strong correlation between measured NO_2 levels and NO_{2-CALC} in all 4 monitors.

PMXBFX DRGTHM

correlation.995 .999 .999 .998

bias +/- precision.16±.75-.29±.25 .39±.33-.10±.25

limits of agreement -1.04 to 1.36 -.70 to.12 -.14 to.92 -.50 to.30

All 4 analyzers provide accurate NO_2 readings in a NO_2/room air gas mixture free of NO. This data further supports the theory that the sampling technique may influence the NO_2 readings. Relatively long sample lines and slow sample flow rates used in the SS analyzers, may increase the dwell time of NO and O_2 and result in falsely high NO_2 readings. Further investigation is required to identify the effect of sampling technique on NO_2 readings with these analyzers.

OF-95-132

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