In previous studies the investigators compared the effects of increased tidal volume (VT) with zero end-expiratory pressures (ZEEP) on oxygenation and arterial concentrations of sevoflurane. The investigators found moderately improved oxygenation and a reduced difference between arterial and exhaled carbon dioxide tension with larger tidal volumes achieved this way. The results were similar to what could be expected from an increase in FRC and also included a more efficient uptake of sevoflurane. The investigators have recently confirmed these findings also in overweight patients.