Humidity and measurement of volatile propofol using MCC-IMS (EDMON)

Abstract

The bedside Exhaled Drug MONitor – EDMON measures exhaled propofol in ppbv every minute based on multi-capillary column – ion mobility spectrometry (MCC-IMS). The MCC pre-separates gas samples, thereby reducing the infuence of the high humidity in human breath. However, preliminary analyses identifed substantial measurement deviations between dry and humid calibration standards. We therefore performed an analytical validation of the EDMON to evaluate the infuence of humidity on measurement performance. A calibration gas generator was used to generate gaseous propofol standards measured by an EDMON device to assess linearity, precision, carry-over, resolution, and the infuence of diferent levels of humidity at 100% and 1.7% (without additional) relative humidity (reference temperature: 37°C). EDMON measurements were roughly half the actual concentration without additional humidity and roughly halved again at 100% relative humidity. Standard concentrations and EDMON values correlated linearly at 100% relative humidity (R²=0.97). The measured values were stable over 100min with a variance≤10% in over 96% of the measurements. Carry-over efects were low with 5% at 100% relative humidity after 5min of equilibration. EDMON measurement resolution at 100% relative humidity was 0.4 and 0.6 ppbv for standard concentrations of 3 ppbv and 41 ppbv. The infuence of humidity on measurement performance was best described by a second-order polynomial function (R²≥0.99) with infuence reaching a maximum at about 70% relative humidity. We conclude that EDMON measurements are strongly infuenced by humidity and should therefore be corrected for sample humidity to obtain accurate estimates of exhaled propofol concentrations.