title: Adaptation of the NDIR technology to 13CO2 breath tests under increased inspiratory O2 concentrations.
abstract: Nondispersive infrared spectroscopy (NDIR) allows the continuous analysis of respiratory gases. Due to its high selectivity, simple and robust setup, and small footprint, it is also used to support (13)CO(2) breath tests to assess bacterial growth in the stomach, gut, or liver function. CO(2) NDIR signals, however, are biased by oxygen in the gas matrix. This complicates NDIR-based breath tests, if the inspired oxygen concentration has to be adjusted to the subject's requirements, or hyperoxia-induced effects were studied. To avoid the oxygen-induced bias, a "dilution" approach was developed: expired gas is mixed with N(2) to lower the oxygen content down to the usual range of 15-20%. Accuracy and precision were tested using synthetic gas mixtures with increasing (13)CO(2)-to-(12)CO(2) ratios ((13)CO(2)/(12)CO(2)), either based on synthetic air with approximately 20% volume O(2) or on pure O(2). For samples with delta(13)C values smaller than 300 (or (13)CO(2)/(12)CO(2) smaller than 0.003), the dilution does not significantly increase the bias in the (13)CO(2)/(12)CO(2) determination, and the within-run imprecision is smaller than 1 delta(13)C. The practical use of this approach was validated in a pig study using a sepsis model reflecting a clinical situation that requires an increased oxygen concentration for respiration. The N(2) dilution eliminated the high bias in NDIR measurement, thus allowing the determination of the impact of oxygenation on glucose oxidation in patients ventilated with increased oxygen.
authors.affiliation: Universitätsklinik für Anästhesiologie Ulm, Sektion APV, 89073 Ulm, Germany. josef.vogt@uni-ulm.de
authors.forename: Josef A
authors.initials: JA
authors.lastname: Vogt
authors.forename: Ulrich
authors.initials: U
authors.lastname: Wachter
authors.forename: Jürgen
authors.initials: J
authors.lastname: Mehring
authors.forename: Peter
authors.initials: P
authors.lastname: Radermacher
authors.forename: Michael
authors.initials: M
authors.lastname: Georgieff
authors.forename: Heinz
authors.initials: H
authors.lastname: Fischer
authors.forename: Uvo
authors.initials: U
authors.lastname: Hölscher
authors.forename: Michael
authors.initials: M
authors.lastname: Moede
authors.forename: Walter
authors.initials: W
authors.lastname: Fabinski
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis; D001944:Breath Tests / Q000379:methods*; D002245:Carbon Dioxide / Q000032:analysis*; D002247:Carbon Isotopes; D004195:Disease Models, Animal; D005260:Female; D041981:Gastrointestinal Tract / Q000382:microbiology; D005947:Glucose / Q000008:administration & dosage; D008297:Male; D010101:Oxygen Consumption; D010538:Peritonitis / Q000150:complications / Q000175:diagnosis*; D011865:Radioisotope Dilution Technique; D015203:Reproducibility of Results; D012121:Respiration, Artificial; D018805:Sepsis / Q000175:diagnosis* / Q000209:etiology; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013552:Swine
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D005947:Glucose