The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

EVALUATION OF FOUR ANALYZERS USED TO MONITOR INHALED NITRIC OXIDE THERAPY.

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

The verification of nitric oxide (NO) doses and the measurement of nitrogen dioxide (NO_2) levels is essential in evaluating physiologic response and ensuring safe delivery during inhaled NO therapy. We evaluated four commercially available NO/NO_2 analyzers, three electrochemical (EC) models; Pulmonox II (PMX), Bedfont NOxBOX (BFX) and Drager PacII NO & 190 NO_2 (DRG), and one chemiluminescence device; Thermoenvironmental 42M (THM). All four analyzers were calibrated according to the manufacturers' specifications. The EC devices were calibrated at 25 cmH_2O pressure. NO from an 800 ppm source tank was titrated into the inspiratory limb of an infant ventilator (VIP Bird). NO concentrations were determined from the equation: NO_{CALC} = NO Source NO Vdot / NO Vdot + Ventilator Vdot. NO Vdot and ventilator Vdot were verified and 7 NO doses ranging from 3 to 80 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, and Ti 0.6 secs. NO and NO_2 levels were measured and recorded for each NO_{CALC} and at a set FiO_2 of .30, .60 and 1.0. Each analyzer was studied independently and 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 measurements were compared to NO_{CALC} and NO_2 levels were compared between each analyzer. There was a strong correlation between measured NO levels and NO_{CALC} in all 4 analyzers (Table 1). NO_2 measurements at NO levels >= 40 ppm are reported in Table 2. The BFX and THM are side-stream analyzers and measured significantly higher NO_2 levels than the PMX and DRG which are main-stream analyzers (p< .001).

Table 1: Correlation between measured NO and NO_{CALC}

PMX BFXDRGTHM

correlation.9991.0 1.0 .997

bias±precision -.06±1.13-.67±34 1.4±1.091.01±1.11

limits of agreement-5.04 to 4.92 -2.15 to .81 -3.38 to 6.18 -3.85 to 5.87

Table 2: NO_2 measurements (ppm); mean ±SD

NO_{CALC} PMX BFXDRG THM

40 .21±.081.0±.25 .52±.17 1.14±.36

60 .29±.081.7±.51 .72±.20 2.60±1.11

80 .54±.172.4±.65 .99±.33 3.40±1].47

All 4 analyzers produced precise and accurate NO measurements and are suitable for the clinical monitoring of inhaled NO doses. The different NO_2 levels may be due to sampling technique. The BFX and THM sample lines and slow sample flow rates may be a source for additional NO_2 production and may result in falsely high NO_2 readings. The effect on NO_2 readings that a decreased sample line length and lumen, and increased sample flow rate, would have on the side-stream analyzers needs further investigation. The choice of monitor will depend on other factors such as cost, portability, availability of alarms and ease of use.

OF-95-133

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