The investigators hypothesized that by inducing and discontinuing anesthesia during CPAP/PEEP and deliberately reducing FIO2 after extubation, postoperative atelectasis would be reduced compared with standard protocols. To test our hypothesis, the investigators studied 1) a control group with no CPAP/PEEP and a FIO2 of 1.0 while breathing spontaneously after extubation, and 2) an intervention group that was on CPAP/PEEP of 6 cmH2O from induction to extubation and that received an FIO2 of 1.0 until extubation and then an FIO2 of 0.3 via a facemask while on CPAP after extubation.