Areas of atelectasis expressed as cm² before and after awakening, in the positive end-expiratory pressure (PEEP) group and the zero PEEP group. The first scan was done at the end of surgery still under anesthesia and mechanical ventilation with PEEP in both groups. The second scan was done at awake state, approximately 30 min after extubation. Computed tomography scans were performed at end expiration 5 mm above the right diaphragm dome. The data are presented as the median, interquartile range (boxes), and range (whiskers), except for observations that were considered outliers (indicated by individual study subject numbers in the two groups, respectively). P = 0.120 for the difference between groups in atelectasis before awakening. P = 0.400 for the difference between groups in change in atelectasis from before to after awakening. P = 0.854 for the difference between groups in postoperative atelectasis.