In vivo evaluation of a new method for chemical analysis of volatile components in the respiratory gas of mechanically ventilated patients *

Abstract

Using the volatile anaesthetic isoflurane as a marker substance a gas chromatographic method for analysis of exhaled gas in mechanically ventilated patients was evaluated. Twelve patients with and 10 patients without preceding isoflurane exposure and seven blank respiratory circuits were investigated. Respiratory gas was sampled at four different sites in the respiratory tubing system. Analysis of volatile components was based upon adsorption onto activated charcoal, desorption by means of microwave energy, gas chromatographic separation and flame ionisation or mass spectrometric detection. Isoflurane concentrations in the blank respiratory circuits, in the control group, and in the inspiratory limb of patients with preceding isoflurane inhalation were at the limit of detection (<10⁻¹² mol/l). In the isoflurane group, isoflurane concentrations in the inspiratory and expiratory limb differed considerably. Using the method described, substances at very low concentrations could be identified as originating in the patient or as coming from the gas delivery system.