Blood samples of 3 ml were drawn from the arterial line into heparinised syringes at 1, 3, 5, 10, 15, 30, 45 and 60 minutes after the start of the sevoflurane administration (totally 27 ml). Arterial oxygen tension (PaO2), oxygen saturation (SaO2) and carbon dioxide tension (PaCO2) will be analysed using an automatic blood gas analyzer (ABL 725™, Radiometer, Copenhagen Denmark). Sevoflurane concentration will be analysed with gas chromatography (GC) on a Perkin-Elmer 3920 gas liquid chromatograph, as previously described.