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Introduction: Protocols using high levels of positive end-expiratory pressure (PEEP) in combination with low tidal volumes have been shown to reduce mortality in patients with severe acute respiratory distress syndrome (ARDS). However, the optimal method for setting PEEP is yet to be defined. It has been shown that respiratory system reactance (Xrs), measured by the forced oscillation technique (FOT) at 5 Hz, may be used to identify the minimal PEEP level required to maintain lung recruitment. The aim of the present study was to evaluate if using Xrs for setting PEEP would improve lung mechanics and reduce lung injury compared to an oxygenation-based approach. Methods: 17 pigs, in which acute lung injury (ALI) was induced by saline lavage, were studied. Animals were randomized into two groups: in the first PEEP was titrated according to Xrs (FOT group), in the control group PEEP was set according to the ARDSNet protocol (ARDSNet group). The duration of the trial was 12 hours. In both groups recruitment maneuvers (RM) were performed every 2 hours, increasing PEEP to 20 cmH(2)O. In the FOT group PEEP was titrated by monitoring Xrs while PEEP was reduced from 20 cmH(2)O in steps of 2 cmH(2)O. PEEP was considered optimal at the step before which Xrs started to decrease. Ventilatory parameters, lung mechanics, blood gases and hemodynamic parameters were recorded hourly. Lung injury was evaluated by histopathological analysis. Results: The PEEP levels set in the FOT group were significantly higher compared to those set in the ARDSNet group during the whole trial. These higher values of PEEP resulted in improved lung mechanics, reduced driving pressure, improved oxygenation, with a trend for higher PaCO(2) and lower systemic and pulmonary pressure. After 12 hours of ventilation, histopathological analysis showed a significantly lower score of lung injury in the FOT group compared to the ARDSNet group. Conclusions: In a lavage model of lung injury a PEEP optimization strate

Background Anaesthesia based on inhalational agents has profound effects on chest wall configuration and breathing pattern. The effects of propofol are less well characterised. The aim of the current study was to evaluate the effects of propofol anaesthesia on chest wall motion during spontaneous breathing and positive pressure ventilation. Methods We studied 16 subjects undergoing elective surgery requiring general anaesthesia. Chest wall volumes were continuously monitored by opto-electronic plethysmography during quiet breathing (QB) in the conscious state, induction of anaesthesia, spontaneous breathing during anaesthesia (SB), pressure support ventilation (PSV) and pressure control ventilation (PCV) after muscle paralysis. Results The total chest wall volume decreased by 0.41 +/- 0.08 l immediately after induction by equal reductions in the rib cage and abdominal volumes. An increase in the rib cage volume was then seen, resulting in total chest wall volumes 0.26 +/- 0.09, 0.24 +/- 0.10, 0.22 +/- 0.10 l lower than baseline, during SB, PSV and PCV, respectively. During QB, rib cage volume displacement corresponded to 34.2 +/- 5.3% of the tidal volume. During SB, PSV and PCV, this increased to 42.2 +/- 4.9%, 48.2 +/- 3.6% and 46.3 +/- 3.2%, respectively, with a corresponding decrease in the abdominal contribution. Breathing was initiated by the rib cage muscles during SB. Conclusion Propofol anaesthesia decreases end-expiratory chest wall volume, with a more pronounced effect on the diaphragm than on the rib cage muscles, which initiate breathing after apnoea.