Potential roles of transpulmonary pressure (P
) and functional residual capacity (FRC) in bedside monitoring of risk of ventilator-induced lung injury (VILI). Negative values of end-expiratory PTP (total positive end-expiratory pressure [PEEPTOT] - end-expiratory esophageal pressure [PesEXP]) suggest collapse in the region of the balloon. Tidal reversal to positive end-inspiratory PTP values (plateau airway pressure [PPLAT] - end-inspiratory esophageal pressure [PesINSP]) suggests potentially damaging tidal opening/collapse cycles. Resting lung volume (FRC) may be used in a 'strain' equation (see text and Table 1) in which end-inspiratory and end-expiratory absolute lung volumes are required, in addition to PEEPTOT and PesEXP. VT: tidal volume, CL: lung compliance.