Evaluation of sevoflurane interference with forensic blood ethanol analysis, including sevoflurane stability, and an authentic case

Sevoflurane, a volatile anesthetic routinely used in clinical settings, was investigated to determine the extent of its interference with in-house forensic blood ethanol analysis. This potential interference could have a significant impact on the analysis and subsequently the interpretation of ethanol in human performance antemortem forensic toxicology casework (e.g. Driving While Under the Influence (DWI) cases). Aqueous samples with ethanol concentrations spanning 0.02-0.40 g/100 mL were fortified with sevoflurane and analyzed using two different dual-column headspace--gas chromatography with flame ionization detection instruments. Sevoflurane was found to elute as an interference peak near ethanol on column 1 (BAC1) and co-elute with ethanol on column 2 (BAC2); the differences were due to the column chemistries. Analyte identification and quantification acceptance criteria monitored included peak-to-valley ratio (resolution) and percent difference between individual column concentrations and the average value of both column concentrations. A 2023 DWI case exhibited potential sevoflurane interference and demonstrated the importance of ethanol reporting acceptance criteria for detecting such interference. In the majority of experiments with sevoflurane and ethanol present in the samples, sevoflurane presence caused failing acceptance criteria to report ethanol results, but if acceptance criteria were met, the ethanol concentration was slightly elevated. An additional sevoflurane stability study showed that the highly volatile sevoflurane could evaporate between analysis and re-analysis of blood samples due to additional tube openings. The decrease of sevoflurane was monitored at each opening of the tube using relative peak areas. HFSC re-analyzes suspected sevoflurane samples, as the additional tube openings could allow sevoflurane to evaporate.