Fig. 1
Left panels: Tidal airway P/V curves (red) of patient A (400 ml), C (300 ml) and E (200 ml) of the Mojoli study. Mid panels: Tidal airway PV curves with lung P/V curve (blue line) through end-expiratory airway P/V points (red dots). Right panels: Lung P/V curves (light blue arrows) of 400 ml tidal volume at the PEEP level where transpulmonary driving pressure (ΔPL) is lowest and thus, least injurious, optimal PEEP (PEEPopt). PLplat is the end-inspiratory transpulmonary plateau pressure of the 400 ml tidal volume, which corresponds to a tidal volume of 6 ml/kg in a person with 70 kg ideal body weight (ibw). The dark blue vertical arrows indicate that PEEP inflation starts in non-dependent lung region (ND) and proceeds towards dependent regions (D) [3]. Mid panels show that in patient A and C, EL/ERS was low at the lowest PEEP level but increased at the highest PEEP level, as seen in extrapulmonary ARDS. In the E patient, EL/ERS was high already at the lowest PEEP level and increased further with increasing PEEP, which indicates a low impact of the chest wall complex on respiratory system mechanics, i.e., a behaviour seen in pulmonary ARDS. The overall lung elastance (ELoa) was 15.5, 15.9 and 36.1 cm H2O/L in patient A, C and E, respectively, (corresponding to overall lung compliance of 64, 63 and 28 ml/cm H2O). In patient A, the lung P/V curve has a classic sigmoid appearance and tidal volume is occurring at more dependent lung regions with increasing PEEP. In patient C, the tidal volume is not transferred towards dependent direction with increasing PEEP. Instead, lung elastance increases from a very high level PEEP step by PEEP step. This indicates a true “baby” lung positioned in the most non-dependent lung region above a more or less consolidated dependent lung. The C patient has a pattern that is similar to patient E but with much higher volumes inflated. One could speculate that this is a patient with mild/moderate emphysema on top of a consolidated lung