|
|
October 17-21, 2009 New Orleans, LA Home Abstract Archive Search Abstracts 2009 Session Grid 2009 Meeting Website Policy Statements ASA Website Feedback 
Visit Anesthesiology.org |
| Previous Abstract | Next Abstract |
| Printable Version |
|
A1642
October 16, 2007 1:30 PM - 3:00 PM Room Room 301 |
| Oxygen Uptake (VO2) Measurement System Based on Novel Luminescence-Quenching On-Airway Oxygen Sensor |
|
Joseph Orr, Ph.D., Lara Brewer, M.S. Amesthesiology, University of Utah, Salt Lake City, Utah |
|
Introduction: Indirect calorimetry systems calculate metabolic rate and calorie consumption from directly measured oxygen uptake (VO2) and carbon dioxide production (VCO2). These systems measure the difference in volume between inspired and expired O2 and CO2 in respiratory gases. Most indirect calorimetry systems designed for use in critical care employ side sampling paramagnetic oxygen analyzers. Side sampling introduces challenges including signal alignment with the flow measurement, sampling tube occlusion and others. Methods: We used a patient simulator based on propane combustion to model oxygen uptake (VO2) and CO2 production (VCO2). We compared the VCO2, VO2 and respiratory quotient as measured by the on-airway system to the standard paramagnetic oxygen sensor type metabolic analyzer (Deltatrac, Datex, Helsinki, Finland). The respiratory quotient (RQ) is the ratio of CO2 production to oxygen consumption. With the simulator burning propane gas, the true respiratory quotient (RQ) is known to be 0.60. Based on previous studies2, we assumed that the VCO2measurements for both systems were accurate. We calculated the true reference VO2 for each setting from the measured VCO2 and the known RQ. We ventilated the patient simulator using a Siemens 900C ventilator at two simulated metabolic rates using three inspired O2 (FiO2) levels at each simulated metabolic rate. The measured VO2 and VCO2 was expected to be the same at each simulated metabolic rate regardless of the inspired oxygen concentration. The measurements (FiO2, VCO2, and VO2) were recorded as they were reported in real time and were compared between monitors. The VO2 results were also compared to the ideal VO2 measurement calculated using the measured VCO2 and the known RQ of 0.60. Results:The average difference in CO2 production between the two systems was 0.5 ± 3.9 ml/min. The average percent difference was 0.3± 2.8%. Figure 1 shows that the inspired oxygen (FiO2) measurements correlated well between monitors (r2 = 0.999). The average oxygen consumption (VO2) error for the Deltatrac monitor was 23 ± 50 ml/minute (5.8 ± 13.9%). The average error for the on-airway, luminescence quenching system was –13 ± 2.5 ml/minute (-5.4±1.3%). The VO2 measurement error using the on-airway system was consistently small across all inspired oxygen levels. The Deltatrac system showed a correlation between percent measurement error and the inspired oxygen concentration. Melendez, et al., found that the Deltatrac tends to measure VO2 too high when the FiO2 is increased2.[figure1]Conclusion: Accurate measurement of oxygen consumption is one of the most challenging applications of respiratory oxygen monitoring. Our data show that an on-airway oxygen analyzer based on luminescence quenching can be applied to provide accurate oxygen uptake measurements. Reference: JA Melendez, M Veronesi, R Barrera, E Ferri, S Midownik; Determination of metabolic monitor errors and precision under clinical conditions, Clinical Nutrition(2001) 20(6): 547-551. Anesthesiology 2007; 107: A1642 |
Figure 1
 |