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A-525
2003 |
| Measurement of Oxygen Uptake and Carbon Dioxide Elimination Utilizing the Bymixer: Validation in a Metabolic Lung Simulator |
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Abraham Rosenbaum, M.D., Christopher W. Kirby, BSc, Peter H. Breen, M.D., F.R.C.P.C. Anesthesiology, University of California-Irvine, Orange, California. |
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Introduction: Indirect calorimetry is a well accepted method for the noninvasive measurement of O2 consumption (VO2) and CO2 elimination (VCO2) in the intensive care unit.1 Most of the present monitoring devices use the Haldane transformation2 for this measurement. Traditionally, it relies solely on the expiratory flow and then uses nitrogen conservation to correct for errors in the flow measurement. Furthermore, it requires mixed gas fractions for the determination of that measurement. Classically, an exhaust gas collection bag or chamber are used for that purpose. We have developed a new clinical bymixer that is interposed in the expiratory limb of the ventilation circuit to measure mixed expired gas fractions. This study tested the accuracy of airway bymixer-flow measurements of VCO2 and VO2 in a novel bench apparatus. Methods: We compared airway bymixer-flow measurements of VCO2 and VO2 over a range of reference values generated by ethanol combustion in a new metabolic lung simulator, which was ventilated by a volume cycled respirator. An airway humidity and temperature sensor3 permitted STPD correction of airway VCO2 and VO2. Results: Bymixer-flow airway measurements of VCO2 and VO2 correlated closely (R2 = 0.995 and 0.994, respectively) with the stoichiometric values generated by ethanol combustion (Figure 1). Limits of agreement for VCO2 and VO2 (ratio analysis) were -3.1± 8.0% and 4.1± 7.7%, respectively (Figure 2). The average (±SD) percent error for airway VCO2 (compared to the stoichiometric value) was -3.4±4.5%. The same error for airway VO2 was 3.8±3.6%. Discussion: The new clinical bymixer, plus basic expired flow and gas fraction measurements, generated clinically accurate determinations of VCO2 and VO2. These measurements are helpful in the assessment of metabolic gas exchange in the critical care unit. In contrast to the gas collection bag or complex metabolic monitor, the bymixer could measure mixed gas concentrations in the inspired or expired limb of the common anesthesia circle ventilation circuit. We intend to explore its advantages in a closed anesthesia circuit. References: 1. Bursztein S et al. Energy metabolism indirect calorimetry, and nutrition. Baltimore, 1st Edition, William & Wilkins 1989; pp. 119-172. 2. Annals of Biomedical Engineering 2000; 28: 1159-1164. 3. U.S. Patent Number 6,014,890; 2000. Supported by NIH grant HL-42637. Anesthesiology 2003; 99: A525 |
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