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 F_iO₂. The purpose of this study was to determine if (a) hood geometry effects NO₂ levels (b) increasing F_iO₂ 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 F_iO₂ = 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 F_iO₂ on NO₂ production was evaluated for the large Nova hood only as the worst case scenario. F_iO₂ 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 F_iO₂ 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 F_iO₂ and NO₂ was 0.983 (p < 0.0001); FiO2 = -0.245 + (0.444 * NO2), R² = 0.967, (assumptions of normality and constant variance validated).

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