title: In vivo validation of the M-COVX metabolic monitor in patients under anaesthesia.
abstract: A practical method of breath-by-breath monitoring of metabolic gas exchange has been developed by GE Healthcare/Datex Ohmeda and incorporated into existing anaesthetic and critical care monitoring systems (M-COVXO). This device relates flow measurements made at the mouth by pneumotachograph to measurements of inspired and expired gas composition by matching the two waveforms thereby allowing continuous, breath-by-breath monitoring of an intubated patient's oxygen uptake and carbon dioxide production. Given that there is a paucity of data comparing this new device against methods more widely used clinically, we tested the device on 11 patients undergoing cardiopulmonary bypass surgery. Using a standard anaesthetic machine (Datex Ohmeda Excel 210 SE) with a semi-closed circle absorber system, oxygen uptake was measured at the mouth continuously throughout the operation at approximately six-second intervals. The data were compared against the reverse Fick method and against standard indirect calorimetry using the Haldane transformation. When compared to the calculated reverse Fick oxygen uptake, a mean difference of +16.5% was found pre-bypass and +9.9% post-bypass, consistent with uptake of oxygen by lung tissue, which is not taken into account by the reverse Fick method. Measurements made comparing the M-COVX metabolic monitor against standard Haldane showed a mean difference of +5.1% pre-bypass and -2.1% post-bypass. Given the ease with which this device can be incorporated into existing anaesthetic monitoring systems and its accuracy in measuring oxygen uptake, the M-COTVX module is an attractive addition to existing perioperative monitoring.
authors.affiliation: Department of Anaesthesia and Perioperative Medicine, The Alfred Hospital, Melbourne, Victoria, Australia. Christopher.Stuart-Andrews@eng.monash.edu.au
authors.forename: C R
authors.initials: CR
authors.lastname: Stuart-Andrews
authors.forename: P
authors.initials: P
authors.lastname: Peyton
authors.forename: G J B
authors.initials: GJ
authors.lastname: Robinson
authors.forename: D
authors.initials: D
authors.lastname: Terry
authors.forename: B
authors.initials: B
authors.lastname: O'Connor
authors.forename: C
authors.initials: C
authors.lastname: Van der Herten
authors.forename: B
authors.initials: B
authors.lastname: Lithgow
mesh_terms: D000368:Aged; D000764:Anesthesia, Closed-Circuit / Q000295:instrumentation* / Q000379:methods; D000776:Anesthesiology / Q000295:instrumentation*; D002245:Carbon Dioxide; D002302:Cardiac Output; D002315:Cardiopulmonary Bypass / Q000379:methods; D004867:Equipment Design; D006801:Humans; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D010101:Oxygen Consumption; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange
chemical_list: D002245:Carbon Dioxide