1997 OPEN FORUM Abstracts
SODA LIME CANISTER USED AS A NO2 SCRUBBER DURING NITRIC OXIDE ADMINISTRATION
John Newhart RCP., F. Wayne Johnson RCP., Richard N. Channick MD. UCSD Medical Center, San Diego Ca.
Introduction: At our institution we have delivered nitric oxide (NO) to patients with ARDS and pulmonary hypertension via NPB 7200 ventilator. A consequence of mixing NO with oxygen in the ventilator or ventilator circuit is the formation of nitrogen dioxide (NO2), a highly toxic gas. Although the EPA time weighted average (8hrs) limit on NO2 is 5ppm., it has been documented that as little as 2ppm can cause cellular change. At our institution the limit for NO2 is 1ppm. We devised an experiment to measure NO2 delivered to the patient in a simulated clinical condition in order to estimate the efficiency of a soda lime canister in removing NO2. Methods: 800ppm NO source is mixed with clinical air in a modified Bird 3800 blender. The outlet of the blender connects to the air inlet of the 7200 ventilator where it mixes with oxygen inside the ventilator. The resulting NO-O2-N2 is delivered to the patient via a standard heated wire ventilator circuit. The NO2 scrubber was placed in the inspiratory limb 12" from the ventilator outlet. NO2 samples were taken pre and post scrubber at FIO2's .50,.70,.90, and NO settings of 10, 20 and 40 ppm as measured post scrubber. A calibrated ElectroChemical NO/NO2 analyzer (Micro Direct Printer Nox) was used for all measurements. Ventilator settings were CMV, Vt 800cc, RR 12, flow 50lpm. Results: Results are concentrations of NO2 pre and / post scrubber expressed in parts per million (ppm).
.50 .70 .90
10ppm .15/.05 .15/.05 .40/.1
NO ppm 20ppm .35/.20 .55/.25 1.35/.30
40ppm 1.0/.5 1.75/.60 3.0/.85
At all settings tested the soda lime cannister maintained a < 1ppm NO2 in the inspiratory limb. The soda lime removed < 1ppm of NO on any setting tested. Conclusion: Commercially manufactured soda lime canisters can be an efficient method of removing NO2 from the ventilator circuit. Issues such as the effect of the canister on ventilator function and the effective life of the soda lime need to be evaluated.