A Microsystem to Measure Respiratory and Anaesthetic Gases During Surgery
Estimation of the concentration of light and volatile anaesthetic gases in the operating arena is usually achieved either with a series of discrete analysers or with a specially designed time-shared mass spectrometer. The cost and maintenance of either system, as well as the bulk of instrumentation and the time-consuming calibration of each device, have been deterrents to their widespread use. A low-cost system, simpler to calibrate, to operate and to maintain has been designed. It operates on the principle of chromatography but without the usual slow responsetime, and the dependency on technical skill. The overall system incorporates two separate microanalysers: one dedicated to the analysis of volatile anaesthetics, the other to permanent gases. Unlike commercially available chromatographs, this system allows analysis of physiological levels of carbon dioxide in the presence of large concentrations of nitrous oxide. Total analysis time for all gases is within 60 s, and the sample volume is less than 0.25 ml. The analysers are designed to be microcomputer compatible, and a built-in autozeroing circuit ensures a virtually drift-free baseline. Once calibrated prior to use, no periodic calibration is required throughout the duration of a case. Because of their microdimensions, the gas analyzers with their inherent power supplies can be housed in a utility drawer found in any conventional anaesthesia cart, making the overall system unobtrusive during routine use.
KeywordsNitrous Oxide Detector Response Periodic Calibration Total Analysis Time Strip Chart Recorder
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