The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

EFFECT OF MASK TYPE, OXYGEN CONCENTRATION, AND FLOW RATE ON BOTH EXHALED CO2 AND RESPIRATORY FREQUENCY MEASUREMENT BY CAPNOGRAPH

Paul F. Nuccio1, Carol T. Spada1, Gerald L. Weinhouse1, Kathleen H. Niebel2, Jonathan B. Waugh3



Background: The potential for dilution effect on capnography measurements while simultaneously delivering oxygen via various types of masks and settings is undetermined. We experimented with five delivery configurations on healthy adults to determine if receiving supplemental oxygen via mask at different concentrations and flow rates may cause a reduction in the end tidal CO2(etCO2) and/or measured respiratory frequency.

Methods: Baseline spirometry, oral temperature, and pulmonary and smoking history were obtained on 14 adult participants (9 female) ages 20-47 years (28.6�8.0, mean�SD) to determine normal lung status. Each volunteer wore the Smart Capnoline Plus H O2 FilterLine (Oridion Capnography Inc.) that provided both oral and nasal CO2 sampling throughout the trial. Five different oxygen delivery configurations using FDA-cleared masks were worn over the CO2 sampling FilterLine for 5 minutes each during testing (masks: 40% air-entrainment, 60% aerosol, 12 L/min non-rebreather, 12 L/min partial rebreather, 8 L/min simple). Ventilation (etCO2, frequency), oxygenation (SpO2) and heart rate were manually recorded each minute along with continuous electronic data extraction using the Capnostream 20� during resting breathing. Comparison of etCO2 and frequency for the mask configurations was done using Friedman's test and Bonferroni post-hoc multiple comparisons test.

Results: The overall mean etCO2 concentration varied from 34.1 to 35.4 for a maximal difference of only 1.3 mm Hg or 3.8% from smallest to highest overall value across mask types. This was not a statistically significant difference (p=0.840) nor was the overall respiratory frequency different (p=0.173).

Conclusion: End tidal CO2 and respiratory frequency were not affected by the type of mask used or by the range of O2 concentrations used in the study. Exhaled CO2 remained undiluted when sampled via both nasal and oral ports. These findings may aid in the implementation of capnography for ventilation monitoring in clinical practice when supplemental oxygen is provided by mask. (Supported in part by Oridion Capnography Inc.)