Comparison of breathing methods for inhalation induction of anaesthesia

We studied healthy female patients, allocated randomly to three breathing regimens for induction of anaesthesia using sevoflurane and oxygen from a co-axial Mapleson D breathing system and a mask, to test the hypothesis that rebreathing reduces the incidence of apnoea associated with loss of consciousness. The non-rebreathing group received sevoflurane in oxygen 6 litre min-1 from the start, doubling in concentration from 0.5% to 8% every 3 breaths. The second group received oxygen 6 litre min-1 for 1 min before sevoflurane was introduced, and the third group received oxygen 3 litre min-1 for 1 min before sevoflurane. The incidence and duration of apnoea were assessed using pneumotachograph and impedance pneumograph recordings, and time to induction of anaesthesia (weight drop) was measured from the time the breathing sequence was started. There was no difference in these times, which were mean 121 (95% confidence values 91-160) s, 117 (69-201) s and 125 (76-192) s, respectively. There was a significant difference in the incidence of apnoea. No apnoea occurred during induction using oxygen 3 litre min-1. Apnoea occurred in five of 15 patients who did not receive oxygen before sevoflurane and in four of 13 who received oxygen 6 litre min-1 (P < 0.05). No patient showed a reduction in pulse oximeter saturation. We conclude that inhalation induction of anaesthesia can be performed reliably in approximately 3 min using sevoflurane in oxygen 3 litre min-1.