The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

EFFECTS OF OXYHOOD GEOMETRY AND OXYGEN CONCENTRATION ON NO2 PRODUCTION

Michael Tracy, RRT, Robert Chatbum, RRT, FAARC University Hospitals of Cleveland, Ohio

BACKGROUND: Previous studies at our institution suggested that nitric oxide (NO) can be delivered to an oxyhood with acceptable levels of nitrogen dioxide (NO2) using a large Nova Tent House (Nova Health Systems, Blackwood, NJ) at a constant FiO2. The purpose of this study was to determine if (a) hood geometry effects NO2 levels (b) increasing FiO2 results in unacceptable levels of NO2 production and (c) oxyhood delivery of NO with poses an environmental threat.

Methods: Three different oxyhoods were set to receive FiO2 = 0.40 at a total flow of 15L/m. NO was then introduced at 40 ppm. Hood brands were: ICN Pharmaceutical Ribavirin hood (ICN Pharmaceuticals, Costa Mesa, CA), ?Oxydome? (Nascor, Australia) and the 7²´7²´7² (small) Nova Tent House. An INO-vent (INO Therapeutics, Clinton, NJ) was used to inject NO and monitor NO, NO2 and O2. The INOvent was calibrated according to the manufacturer's instructions. One measurement was made for each experimental condition after a 5 minute stabilization period. The injector module was placed on the inlet side of the humidifier and the sample line was suspended in the center of each hood. Environmental exposure to NO and NO2 was assessed by sampling at 10, 30 and 60 cm away from the head opening of the hood. Peak exposure level (PEL) was obtained by lifting up the hood and measuring the highest NO/NO2 concentrations at 30 cm. The effect of increasing FiO2 on NO2 production was evaluated for the large Nova hood only as the worst case scenario. FiO2 was varied in 0.10 increments from 0.40 to 1.00. Correlation was assessed with Pearson product moment correlation and linear regression.

Results: Measured NO levels ranged from 36 to 38 ppm with a resultant FiO2 ranging from 0.36 to 0.28. NO2 was 0.7 ppm for the ICN hood and 0.5 ppm for the other two. NO/NO2 data outside the hoods are shown below. The correlation between FiO2 and NO2 was 0.983 (p < 0.0001); FiO2 = -0.245 + (0.444 * NO2), R2 = 0.967, (assumptions of normality and constant variance validated).

Environmental Exposure Data
10 cm 30 cm 60 cm PEL@30cm
ICN 33 / 0.6 0.8 / 0.0 0.3 / 0.0 2.5 / 0.0
Oxydome 30 / 0.4 1.3 / 0.0 0.5 / 0.0 3.8 / 0.0
Nova small 25 / 0.2 0.6 / 0.0 0.3 / 0.0 1.7 / 0.0
Nova large 37 / 0.9 1.5 / 0.0 0.6 / 0.0 3.5 / 0.0

The ICN scavenging system did not decrease environmental exposure to NO/NO2.

Conclusions: All oxyhoods satisfactorily deliver NO/O2 mixtures. Scavenging is not necessary. At any significant distance from the hood NO and NO2 values are well below OSHA guidelines (NO TWA = 25ppm, NO2 = 3ppm, NO PEL = 25 ppm and NO2 STEL = 5ppm). Higher FIO2 places the patient at increased risk of NO2 exposure. Respiratory Care departments delivering NO/O2 mixtures via oxyhood should establish preset mixture limits to avoid placing their patients at increased risk.

OF-99-021

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