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October 16-20, 2010 San Diego, CA Home Abstract Archive Search Abstracts 2010 Session Grid 2010 Meeting Website Policy Statements ASA Website Feedback 
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A1689
October 22, 2008 9:00 AM - 11:00 AM Room Hall E2-Area G, |
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| Evaluation in Volunteers of a VO2 Measurement System Based on a Novel On-Airway Oxygen Sensor | ||||||||||||||||
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Joseph A. Orr, Ph.D., Lara M. Brewer, M.S. Anesthesiology, University of Utah, Salt Lake City, Utah |
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Background: Indirect calorimetry is useful for determining patient feeding requirements and for assessing the status of patients with sepsis and other disease states such as malignant hyperthermia. We evaluated a prototype system that uses mainstream sensors to acquire the breath-by-breath O2, CO2 and flow signals needed for indirect calorimetry (Philips Medical Systems, Wallingford, CT). The novel on-airway oxygen sensor uses the principle of photo-luminescence quenching to provide oxygen measurements 100 times per second. We used this oxygen signal along with signals from on-airway CO2 and flow sensors to calculate breath-by-breath VO2. We compared the oxygen uptake (VO2) measurements from the on-airway sensors against the VO2 measurements from the a mixing chamber type metabolic cart (Deltatrac, Datex, Helsinki, Finland) in healthy volunteers. Methods: Using a protocol approved by our institution, we requested 20 healthy human volunteers (10 men, 10 women) to breathe normally through a mouthpiece connected to the on-airway sensors. One-way valves were used to direct the expired gas through the Deltatrac mixing chamber. The two phases of the experiment lasted until steady state was reached (approximately 30 minutes). During each phase, the subjects inspired either room air (21% oxygen) or 40% oxygen in nitrogen. Recordings of the oxygen uptake (VO2) and carbon dioxide elimination (VCO2) were taken from both monitors throughout the experiment and average values measured during steady state were compared. Results: The table below shows the average differences between the two monitors for measured VO2 and VCO2 data.[table1]The average difference in VO2was -5.9 ±10.8 ml/min (-2.2±4.1%) when subjects breathed air and 5.1±18.1 ml/min (1.8±6.3%) when subjects breathed 40% oxygen. The plot shows the Bland-Altman difference and the limits of agreement.[figure1]Discussion: The on-airway sensors appeared to measure VO2 with adequate agreement and repeatability that they could be used interchangeably with the Deltatrac device. The bias and limits of agreement were larger at 40% inspired oxygen, but it has also been shown that the Deltatrac has more error at a higher oxygen level. This new mainstream O2, CO2 and flow sensor shows promise of automated and reliable indirect calorimetry for the critical care setting. The primary drawback of conventional indirect calorimetry systems is that they are based on mixing chambers and require separate sampling locations for inspired and expired gas concentrations. More contemporary indirect calorimeters make us of sidestream gas sampling, which can also be problematic because of difficulties with signal alignment in the presence of ventilator settings such as positive end-expiratory pressure (PEEP) and potential for fluid buildup leading to obstructions in the sampling tube. Anesthesiology 2008; 109 A1689 |
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