Effects of inhalational anaesthesia with low tidal volume ventilation on end-tidal sevoflurane and carbon dioxide concentrations: prospective randomized study

Abstract

ObjectiveWe investigated how ventilation with low tidal volumes affects the pharmacokinetics of sevoflurane uptake during the first minutes of inhaled anaesthesia. MethodsForty-eight patients scheduled for lung resection were randomly assigned to three groups. Patients in group 1, 2 and 3 received 3% sevoflurane for 3min via face mask and controlled ventilation with a tidal volume of 2.2, 8 and 12mlkg−1, respectively (Phase 1). After tracheal intubation (Phase 2), 3% sevoflurane was supplied for 2min using a tidal volume of 8mlkg−1 (Phase 3). ResultsEnd-tidal sevoflurane concentrations were significantly higher in group 1 at the end of phase 1 and lower at the end of phase 2 than in the other groups as follows: median of 2.5%, 2.2% and 2.3% in phase 1 for groups 1, 2 and 3, respectively (P<0.001); and 1.7%, 2.1% and 2.0% in phase 2, respectively (P<0.001). End-tidal carbon dioxide values in group 1 were significantly lower at the end of phase 1 and higher at the end of phase 2 than in the other groups as follows: median of 16.5, 31 and 29.5mmHg in phase 1 for groups 1, 2 and 3, respectively (P<0.001); and 46.2, 36 and 33.5mmHg in phase 2, respectively (P<0.001). ConclusionWhen sevoflurane is administered with tidal volume approximating the airway dead space volume, end-tidal sevoflurane and end-tidal carbon dioxide may not correctly reflect the concentration of these gases in the alveoli, leading to misinterpretation of expired gas data.