Optimisation of positive end-expiratory pressure by forced oscillation technique in a lavage model of acute lung injury

We evaluated whether oscillatory compliance (C-X5) measured by forced oscillation technique (FOT) at 5 Hz may be useful for positive end-expiratory pressure (PEEP) optimisation. We studied seven pigs in which lung injury was induced by broncho-alveolar lavage. The animals were ventilated in volume control mode with a tidal volume of 6 ml/kg. Forced oscillations were superimposed on the ventilation waveform for the assessment of respiratory mechanics. PEEP was increased from 0 to 24 cmH(2)O in steps of 4 cmH(2)O and subsequently decreased from 24 to 0 in steps of 2 cmH(2)O. At each 8-min step, a CT scan was acquired during an end-expiratory hold, and blood gas analysis was performed. C-X5 was monitored continuously, and data relative to the expiratory hold were selected and averaged for comparison with CT and oxygenation. Open lung PEEP (PEEPol) was defined as the level of PEEP corresponding to the maximum value of C-X5 on the decremental limb of the PEEP trial. PEEPol was on average 13.4 (+/- 1.0) cmH(2)O. For higher levels of PEEP, there were no significant changes in the amount of non-aerated tissue (V-tissNA%). In contrast, when PEEP was reduced below PEEPol, V-tissNA% dramatically increased. PEEPol was able to prevent a 5% drop in V-tissNA% with 100% sensitivity and 92% specificity. At PEEPol V-tissNA% was significantly lower than at the corresponding PEEP level on the incremental limb. The assessment of C-X5 allowed the definition of PEEPol to be in agreement with CT data. Thus, FOT measurements of C-X5 may provide a non-invasive bedside tool for PEEP titration.