Photoacoustic detection of propofol in breath gas for monitoring depth of anaesthesia: from bench to bedside.

Abstract

Ensuring adequate depth of i.v. anaesthesia by measuring propofol in breath gas could increase patient safety. Mass spectrometry, representing the reference standard of propofol breath gas measurements, is not feasible in routine clinical practice; hence, a photoacoustic sensor was developed. The photoacoustic sensor quantifies propofol concentration in gas via the sound waves emitted by propofol molecules excited by light of specific wavelength and frequency. We studied the performance of the new sensor in propofol test gas, gas sampling bags filled with breath gas from different patients, and performed real-time measurements in patients undergoing propofol anaesthesia in comparison to ion-molecule reaction mass spectrometry. In test gas, photoacoustic and mass spectrometry correlated with an R² of 0.9975 in a range from 2.5 to 60 ppb. In gas sampling bags, propofol could be detected with both methods. Bland-Altman analysis of propofol general anaesthesia over 18 h in 10 patients revealed a mean propofol difference of -0.02 ppb (standard deviation 3.31) between mass spectrometry and photoacoustic measurements in breath gas, ranging from 4 to 47 ppb. Photoacoustic measurement of propofol concentration in breath gas is feasible with high accuracy in clinical applications.