Results from quantitative computer tomography and blood gas analysis.

Values are given as median (interquartile range). Data for sheep were obtained for atelectatic (first column) and recruited lungs. Data in the second column were obtained after applying a recruitment manoeuvre (RM) and subsequent ventilation with PEEP of 10 cm H2O for 10 minutes. Data in the third column were obtained after applying another RM and ventilation with PEEP of 20 cm H2O for 10 minutes. Pigs were studied during baseline conditions (atelectasis in otherwise normal lungs) and 12 hours after induction of acute respiratory distress syndrome (ARDS). The PEEP in the ARDS column was chosen according to different lung protective ventilation strategies. N, number of animals studied; Vtotal, total lung volume; Mtotal, total lung mass; Mhyper, mass of the hyperaerated (-901 to -1000 HU); Mnormal, mass of the normally aerated (-501 to -900 HU); Mpoor, mass of the poorly aerated (-101 to -500 HU); Matelectasis, mass of the atelectatic lung compartment (-100 to +100 HU). Weights of differently aerated lung compartments were calculated as percentage of Mtotal. Atelectasis was also calculated as volume and expressed as percentage of Vtotal. All blood gases were obtained after short-term ventilation with pure oxygen for five minutes. We transformed PaO2 values logarithmically (lnPaO2) to linearize the relationship between PaO2 and atelectasis. Shunt was calculated using Berggren’s approach. As the effects of PEEP or RM on lung aeration were no endpoints of the present study and subgroups were very small, statistical between-group comparison was omitted.