The investigators propose a new wash-in technique for sevoflurane low flow anesthesia with
fresh gas flow of O2:N2O or O2:air 1:1 L/min with sevoflurane 8%.
The objective of this study is to identify time to achieve alveolar concentration of
sevoflurane at 1, 1.5, 2, 2.5, 3, and 3.5%