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

Purpose 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. Methods 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. Results Open lung PEEP (PEEP ol ) was defined as the level of PEEP corresponding to the maximum value of C X5 on the decremental limb of the PEEP trial. PEEP ol 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 PEEP ol , V tissNA % dramatically increased. PEEP ol was able to prevent a 5% drop in V tissNA % with 100% sensitivity and 92% specificity. At PEEP ol V tissNA % was significantly lower than at the corresponding PEEP level on the incremental limb. Conclusions The assessment of C X5 allowed the definition of PEEP ol to be in agreement with CT data. Thus, FOT measurements of C X5 may provide a non-invasive bedside tool for PEEP titration.