Fig. 1

Left panel: Lung P/V curves of patients 1 and 3 with overall lung compliance of 25 and 61 ml/cmH₂O respectively. Overall lung compliance was calculated as end-inspiratory lung volume at the highest PEEP level (12 cmH₂O) divided by end-inspiratory transpulmonary pressure at the highest PEEP level minus 6 cmH₂O (lowest PEEP level). Circles with red filling: end-expiratory transpulmonary pressure (= PEEP). Circles without filling: end-inspiratory transpulmonary pressure. Magenta arrows: tidal lung P/V curves at optimal PEEP obtained by graphical plotting from the lung P/V curve. Data of optimal PEEP tidal volume in italics: VT = tidal volume, ΔPL = transpulmonary driving pressure, CL = lung compliance, PEEP_opt = optimal PEEP level, PL_plat = end-inspiratory transpulmonary pressure. Right panel: Light gray lung P/V curves of patients 1 and 3 can be used as clinical decision support as a tidal lung P/V curve with any combination of PEEP and VT will be positioned on the complete lung P/V curve. This makes it possible to estimate the effect of changes in PEEP and tidal volume. In this case, the tidal lung P/V curves (black arrows) are depicted starting from PEEP 12 cmH₂O. In patient 3 with a moderately decreased overall lung compliance to 61 ml/cmH₂O (“normal” lung compliance 90–110 ml/cmH₂O [3]), transpulmonary driving pressure increases marginally and remains within safe limit, i.e., the patient responds favorably to PEEP. In patient 1, an increase in PEEP to 12 cmH₂O results in a ΔPL 40% higher almost 13 cmH₂O than at PEEP 9 cmH₂O with significant risk of ventilation induced lung injury