Establishing the relationship between FGF/MV and FI/FD, and determining the saturation state of sevoflurane anaesthesia during the induction phase and factors affecting nonrespiratory tract ejection volume.

Objectives: To investigate (i) the relationship between the ratio of fresh gas flow to min volume (FGF/MV) and the ratio of the fraction of inspired sevoflurane to the delivered concentration of sevoflurane (FI/FD); (ii) to establish the saturation state of sevoflurane anaesthesia and factors affecting the volume of ejected sevoflurane through the nonrespiratory tract route (nVERT) during the saturation state.
Methods: Two studies were undertaken in patients with cancer, scheduled to undergo surgery. All patients received tracheal intubation and inhaled sevoflurane. In study 1, anaesthesia parameters were fixed, the initial FD of sevoflurane was 2.2% vol and the FGF/MV was set to 0.2, 0.3, 0.4 and 1.0 in groups A, B, C and D, respectively. In study 2, FGF = MV and the initial FD of sevoflurane was 2.2% vol, but the tidal volume (TV) was set to 6, 8 or 10 ml/kg in groups I, II and III, respectively.
Results: Study 1 (n = 60) showed a positive relationship between FI/FD and FGF/MV. In study 2 (n = 60), when TV was fixed, nVERT increased during the saturation state as FD increased; when FD was fixed, nVERT remained stable, despite increased TV.
Conclusions: FI/FD is positively associated with FGF/MV; nVERT is affected by FD but not TV.