Optimised NDIR technology for 13CO2 breath tests of i.e. drug/drug-interactions or gastric emptying for intensive care patients: New diagnostic opportunities

Abstract

Measurement devices that support CO2 breath tests on an intensive care unit should a) monitor the δ13C release curve over time for reliable data interpretation b) provide results right after sampling and c) be small and easy to handle. NDIR technology could satisfy these requirements, but is sensitive to changes in the sample O2 and CO2 content, which might occur for intensive care patients. These interferences, due to pressure broadening in the hyperfine spectrum, were corrected by a calibration method, where measured δ13C values are expressed as basal value + slope x δ13C(sample), where basal value and slope were confined to depend on the O2 and CO 2 interferences. These functions were determined by fitting measured δ13C values to the corresponding model pre-dictions, with sufficient agreement between both. The slope function turned out to be linear in the interferences and the basal value function nonlinear. The calibration samples, necessary for their characterization can be generated starting from a few, user provided samples, using a machine-built-in gas mixing system. Hence, the combined and O2 impact can be corrected by an on-site calibration method and NDIR technology can be used for bed-side monitoring in an ICU. It paves the way for clinically and economically relevant 13C-breath tests like those for gastric emptying or drug/drug interactions. © 2009 Springer-Verlag.