SESSION TYPE: Respiratory Support Posters
PRESENTED ON: Wednesday, October 24, 2012, 2012 at 01:30 PM - 02:30 PM
PURPOSE: During an experiment to determine if therapeutic gases such as oxygen and heliox at flowrates of 10 and 15 L/min affect the accuracy of capnographic measurements, we identified what may be a gender difference in capnography and pulse oximetry measurements.
METHODS: We measured ETCO2 and RR by capnography in 20 adults (15 ♀, 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 at rest. Participants were distracted by watching a movie to help maintain a steady breathing pattern and were coached to keep their rate between 10-20 bpm if needed. A 6 minute washout period occurred between each 6 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±SD), 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 vs. 10 L/min, p = 0.759; 0 vs. 15 L/min, p=0.642; 10 vs. 15 L/min, p=0.865). Multivariate analysis revealed a fairly large gender effect size (1.2 SD) for ETCO2 data but no significant association with RR. The gender effect size for SpO2 and PR data, 0.82 and 0.99 SDs respectively were also large. Although this was based upon a small sample, this difference between ♂ and ♀ occurred in spite of using a normal group at resting conditions. ETCO2 mean/SD in mm Hg: 35.08/4.21 (♀), 40.15/2.96 (♂); SpO2 in %: 98.98/1.17 (♀), 97.97/1.14 (♂); PR in beats/min: 79.22/13.55 (♀), 63.34/14.51 (♂).
CONCLUSIONS: While the data for the primary study question revealed no differences, ETCO2 was different for gender but that difference could not be attributed to a change in RR. The SpO2 and PR were also different for ♂ and ♀ participants. The difference could be related to women on average having a lower diffusing capacity, smaller airway diameter and lung volumes than men, the women may have had a psychophysiological response to being closely observed, and/or greater caffeine consumption by the female group.
CLINICAL IMPLICATIONS: Although there is no distinction between genders for normal ETCO2 range, these results indicate the possibility such a distinction may be merited. Further studies are needed to determine if this is a true effect.
DISCLOSURE: Jonathan Waugh: Consultant fee, speaker bureau, advisory committee, etc.: Consultant for study sponsor
David Vines: Grant monies (from industry related sources): Participant in mulit-center study also sponsored by Oridion Capnography, the sponsor of this study.
The following authors have nothing to disclose: Donna Gardner
No Product/Research Disclosure InformationUniversity of Alabama at Birmingham, Birmingham, AL