Fig. 1. Computerized tomography (CT) protocol. Spiral CT was performed at two occasions in 23 of 30 patients. Spiral CT was done before and after induction of anesthesia in 6 patients and before and 20 min after intervention in 17 patients. There were 6 patients in the PEEP and RM + ZEEP groups and 5 patients in the RM + PEEP group. Single slices were done separately and also retrieved from the spiral CT scans, so that single slices 1 cm above the diaphragm could be analyzed in all 30 patients at all four time points. CT = computerized tomography, PEEP = positive end-expiratory pressure, RM = recruitment maneuver, ZEEP = zero end-expiratory pressure.