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October 17-21, 2009 New Orleans, LA Home Abstract Archive Search Abstracts 2009 Session Grid 2009 Meeting Website Policy Statements ASA Website Feedback 
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A1644
October 16, 2007 1:30 PM - 3:00 PM Room Room 301 |
| Functional Residual Capacity Measurement Using a New, On-Airway Oxygen Sensor |
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Lara Brewer, M.S., Joseph Orr, Ph.D. Anesthesiology, University of Utah Health Sciences Center, Salt Lake City, Utah |
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Introduction: Functional Residual Capacity (FRC) is the volume of gas left in the lungs at the end of each breath; having sufficiently large FRC is critical for gas exchange. The FRC measurement may be a valuable parameter for use during PEEP titration in accordance with the goals of an open-lung ventilation strategy. The nitrogen washout method of FRC measurement evaluates the volume of excreted nitrogen and the corresponding change in nitrogen concentration to calculate FRC during mechanical ventilation. We calculated N2 concentration as the balance gas, assuming all gas that is neither O2 nor CO2 is nitrogen. The aim of this study was to use a new, integrated oxygen, carbon dioxide and flow sensor to measure FRC in a bench setup. Methods: We used a new, fast on-airway oxygen sensor (Respironics, Inc, Carlsbad, CA) based on the photo-luminescence quenching principle. This new O2 sensor, along with the integrated airway CO2 and flow sensors, was used to calculate nitrogen levels and nitrogen volumes in order to measure the Functional Residual Capacity (FRC) of a simulated lung (TTL, Michigan Instruments, Grand Rapids, MI). The test lung was modified to simulate gas exchange by adding a propane burner which consumes oxygen while producing carbon dioxide at precise rates and proportion during mechanical ventilation. Using the modified test lung, we collected respiratory data and analyzed the nitrogen wash-in signal at three different FRC volume settings and two different tidal volume and respiratory rate combinations. Regression analysis was used to compare the measured and actual FRC volumes. The lung simulator was ventilated with the Esprit ventilator (Respironics, Inc, Carlsbad, CA) with two different settings: 1) tidal volume of 520 mL; respiratory rate of 13 and 2) tidal volume of 750 mL; respiratory rate of 9. The inspired oxygen was decreased from 70% to 30% and the subsequent nitrogen wash-in signal was analyzed to calculate the FRC. FRC was calculated as the ratio of the volume of nitrogen eliminated to the corresponding change in nitrogen concentration. The FRC of the system was measured at three FRC levels. Results: Regression analysis between the measured and actual values yielded an r2 of 0.989 and a slope of 0.914 (Figure 1). Compared to the known reference values, the average error was -6 mL. No significant difference was observed between the bias, regression coefficient, or slope for either of the ventilation settings.[figure1]Discussion: The on-airway oxygen sensor provided reliable signals that were useful for accurate FRC measurements. The on-airway sensor also houses flow and carbon dioxide sensors, which if used in combination with the oxygen signal, could make possible several other measures related to cardiopulmonary health. The advantage of the on-airway sensors is that the signals do not have to be corrected for any delay introduced by sidestream sampling. Future work will involve FRC measurement in human subjects. Anesthesiology 2007; 107: A1644 |
Figure 1
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