The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

Addition of Humidifierto Avoid “Dry Sample Gas” AlarmWhile Administering NO Via Nasal Cannula with the INOvent

John Newhart,CRTT, RCP; Timothy Morris, MD; UCD MEdical Center, San Diego, CA

Background: The Datex OhmedaINOvent (Datex/Ohmeda Madison, WI) is used to deliver inhaled nitric oxide (INO)to mechanically ventilated patients as well as spontaneously breathing patients.The INOvent was designed to sample humidified gas from a ventilator circuit.When using the nasal cannula as described in the INOvent manual, dry gas isdrawn through the sample line (0% RH). After a period of time this causes alow priority alarm “dry sample gas” (DSG) with both visual and audibleindicators. In addition to the alarm, dry sample gas has the effect of shorteningthe lifespan of the nitric oxide and nitrogen dioxide fuel cells. By placinga bubble humidifier in the gas stream that blows through the injector modulethe alarm can be prevented. The injector module uses hot-film technology toaccurately determineflow of gas in a vent circuit, nasal cannula etc. Inaccurateflow measurement will in turn cause inaccurate NO dosing. Therefore any condensationcaused by the humidifier would be of concern. Our study examined the abilityof the humidifier to prevent theDSG alarm as well as avoiding condensation inthe injector module.

Methods: 100% oxygen was passedthrough a standard flowmeter into an AquaPak bubble humidifier (Hudson RCI,Temecula CA). The humidified gas was introduced to te injector module of theINOvent via standard oxygen tubing where NO is injected into the gas stream.The NO, O2, N2 flows into a 6" long 22 mm diameter corrugated tube thatserves as a mixing chamber. The sample line is placed at the outlet of the mixingchamber and draws 230 cc/min into the INOvent analyzer. Relative humidity wasdetermined by a calibrated model 37000 Cole Parmer hygrometer (Cole Parmer VernonHills, Illinois). We ran the INOvent as described set to deliver 20 ppm NO with31pm O2 as a carrier gas for a 66-hour period.

Results: The DSG alarm wasnot activated. The NO dose held constant at 20 ppm indicating proper functionof the flowsensor in the injector modul. Relative humidity in the sample linewas 66%. We also ran a series of short tests to measure %RH at O2 flows at 1-6lpmin 1lpm increments (see table).

Conclusion: At the testedNO dosage and O2 flowrate, the humidity was maintained high enough to preventthe DSG alarm but dry enough not to cause condensation in the injector module.Within the parameters of our study, addition of a bubble humidifier can safelyavoid the “dry sample gas” alarm on the INOvent when administeringINO through a nasal cannula.


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