INTELSENS · Integrated Laser Sensor for Exhaled Anaesthetic Agent Monitoring

Integrated laser sensor for exhaled anaesthetic agent monitoring

Through the INTELSENS project we pioneered technology for the optical detection of propofol, which is intravenously administered and the most widely used anaesthetic drug during surgery. A new optical sensing concept was developed for detecting trace levels of propofol in the exhaled breath. The results will guide future developments of on line anaesthetic sensors for propoful to be used in clinical environments. Propofol (2,6-diisopropylphenol) is widely used with hundreds of thousands of doses administered each year in the UK alone, yet, alarmingly, there are currently no viable methods for monitoring propofol concentration in patients' blood plasma online during surgery. Consequently the effectiveness of propofol induced anaesthesia is only symptomatically assessed, using a subjective and unsophisticated point scoring system. An online capability to monitor propofol levels would dramatically improve the level of control over its administration. Quality of care would be improved by tailoring dosage to individuals' needs, reducing clinical recovery times and patient aftercare with associated cost benefits. Upon injection, propofol is transported into the blood stream and trace fractions of the drug appear in the exhaled breath. In medical feasibility studies using mass spectrometry and gas chromatography propofol levels in parts-per-billion by volume (ppb) range had previously been estimated but the techniques were unsuitable for operation in theatre. A literature survey revealed that no attempts of optical detection had been made and data on absorption cross sections of gas phase propofol were not available. These were therefore measured by us for spectral features in the ultraviolet and infrared regions to inform an optimal strategy optical detection of propofol. The absorption cross-sections in the mid-infrared were quantified by Fourier transform spectrometry. A photoacoustic spectroscopy (PAS) set-up was built for the UV absorption measurements. Detection by PAS was subsequently deemed the most promising route and a dedicated PAS system developed for propofol detection. Using laser excitation in the 260-270 nm spectral range we reached a 1 ppb detection limit with this sensor using calibrated samples generated in a permeation tube system. In a parallel development we developed a strategy to explore the use of broad bandwidth cavity enhanced absorption spectroscopy using supercontinuum radiation for exhaled breath analysis leading to a new technology that was featured as a 'research highlight' in Nature Photonics, Vol. 2, 535 (2008). The project proved the concept beyond doubt and was accomplished through active collaboration between physicists, chemical engineers, medical professionals and commercial medical system developers. The results have raised interest in other research institutes and industrial system manufacturers. A follow-on project is aimed at a clinical evaluation of the PAS technique for online propofol monitoring in patients undergoing surgery. The novel CEAS techniques has furthermore shown great potential also beyond the current application in cross-disciplinary application fields such as atmospheric trace gas sensing, exhaled breath disease diagnostics, industrial process monitoring as well as pollutant detection in the liquid phase. Contact details Dr Clemens F. Kaminski Department of Chemical Engineering and Biotechnology University of Cambridge New Museums Site, Pembroke Street Cambridge CB2 3RA, UK Telephone +44(0)1223 334777, Fax +44(0)1223 334796 Email: cfk23@cam.ac.uk http://laser.ceb.cam.ac.uk

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