title: Continuous measurement of multiple inert and respiratory gas exchange in an anaesthetic breathing system by continuous indirect calorimetry.
abstract: A method was tested which permits continuous monitoring from a breathing system of the rate of uptake of multiple gas species, such as occurs in patients during inhalational anaesthesia. The method is an indirect calorimetry technique which uses fresh gas rotameters for control, regulation and measurement of the gas flows into the system, with continuous sampling of mixed exhaust gas, and frequent automated recalibration to maintain accuracy. Its accuracy was tested in 16 patients undergoing pre-cardiopulmonary bypass coronary artery surgery, breathing mixtures of oxygen/air and sevoflurane with/without nitrous oxide, by comparison with the reverse Fick method. Overall mean bias [95% confidence interval (CI)] of rate of uptake was 17.9 [7.3 to 28.5] ml min(-1) for oxygen, 0.04 [-0.42 to 0.50] ml min(-1) for sevoflurane, 10.9 [-16.1 to 37.8] for CO(2), and 8.8 [-14.8 to 32.4] ml min(-1) for nitrous oxide where present. The method proved to be accurate and precise, and allows continuous monitoring of exchange of multiple gases using standard gas analysis devices.
authors.affiliation: Department of Electrical & Computer System Engineering, Faculty of Engineering, Monash University, Clayton Campus, Building 72, Clayton, VIC, 3800, Australia. Christopher.Stuart-Andrews@eng.monash.edu.au
authors.forename: Christopher
authors.initials: C
authors.lastname: Stuart-Andrews
authors.forename: Philip
authors.initials: P
authors.lastname: Peyton
authors.forename: Craig
authors.initials: C
authors.lastname: Humphries
authors.forename: Gavin
authors.initials: G
authors.lastname: Robinson
authors.forename: Brian
authors.initials: B
authors.lastname: Lithgow
mesh_terms: D000465:Algorithms; D000776:Anesthesiology / Q000295:instrumentation*; D002151:Calorimetry / Q000295:instrumentation* / Q000379:methods; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017022:Flow Injection Analysis / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D015203:Reproducibility of Results; D015656:Respiratory Mechanics / Q000502:physiology*; D012680:Sensitivity and Specificity; D013147:Spirometry / Q000295:instrumentation*