Mass spectrometer artifact: Simultaneous detection of two volatile anesthetics

In several cases, a mass spectrometer indicated that both enflurane and isoflurane were being detected while only isoflurane was in use. The concentration of expired enflurane reported was always higher than the inspired concentration, but never exceeded 0.66% regardless of the concentration of isoflurane. Such mass spectrometer readings may be evidence of vaporizer contamination or malfunction of the vaporizer; however, in this case, the mass spectrometer was found to be out of calibration. Because mass spectrometers are recent additions to clinical equipment, procedures for routine calibration and maintenance must be carefully scrutinized and evaluated.