The Science Journal of the American Association for Respiratory Care

2010 OPEN FORUM Abstracts

EFFECT OF HELIOX ON END-TIDAL CO2 AND RESPIRATORY RATE MEASUREMENT IN HEALTHY ADULTS.

Donna D. Gardner1, David L. Vines2, Richard B. Wettstein1, Jonathan B. Waugh3; 1Department of Respiratory Care, University of Texas health science Center at San Antonio, San Antonio, TX; 2Department of Respiratory Care, Rush University Medical Center, Chicago, IL; 3Clinical and Diagnostic Sciences, University of Alabama at Birmingham, Birmingham, AL

Background: Capnography is a non-invasive method of monitoring ventilator status in the clinical setting. Therapeutic gases delivered by inhalation (O2, N2O, NO, He, anesthetics) may affect the accuracy of capnographic measurements (Colman Y. J Clin Monit 1999;15:403-9). Oridion Capnography Inc. (Needham, MA), claims to have a technology that is unaffected by heliox and anesthesia gases. Our goal was to determine if heliox gas delivered through a mask, and/or flow rate of inspired gas affect this technology’s capnographic measurements of end-tidal CO2 (EtCO2) and respiratory rate (RR). Methods: We measured EtCO2 and RR by capnography in 20 adult volunteers (15 female, ages 20-36 yrs.) with normal spirometry as they breathed heliox (gas mixture of 20% oxygen and 80% helium) via a non-rebreather mask compared to breathing room air (20.9% oxygen and 79.1% nitrogen) at rest. Participants were distracted by watching a video movie to help maintain a steady breathing pattern and were coached to keep their frequency between 10-20 bpm if needed. A six minute washout period occurred between each six minute level of testing. Results: A mixed models analysis revealed that the average EtCO2 for all subjects and flow rates while breathing heliox, 36.9±4.5 mm Hg (mean±standard deviation), was not different (p = 0.501, alpha-level of 0.05) from the value while breathing room air, 36.0±4.5 mm Hg. Repeated measurements on each of the same subjects over 6 minute periods of breathing spontaneously (0 L/min), with 10 L/min flow rate, and with 15 L/min flow rate showed no difference in EtCO2 related to flow (0 L/min vs. 10 L/min, p = 0.759; 0 L/min vs. 15 L/min, p=0.642; 10 L/min vs. 15 L/min, p=0.865; see table). Conclusions: Breathing heliox caused no difference in EtCO2 and RR measurement using a Capnostream™ 20 capnography monitor during resting breathing in this group of young adults with normal spirometry. These same measurements were not affected by differing flow rates of heliox or ambient air compared to breathing with no mask. This has practice implications for both intubated and nonintubated patients receiving heliox in emergent and critical care settings. Sponsored Research - Funded by Oridion Capnography Inc. Effect of Gas Mixture and Flow Rate on Capnostream Measures