Figure 2.

Effects on driving pressure and stress index of the application of the same tidal volume on lungs with different characteristics. In lungs with relevant loss of aeration and poor recruitment potential, the tidal volume is distributed to a small aerated volume, which undergoes tidal hyperinflation, with very high ∆P and stress index well above 1 (A). In similar conditions but with lungs that can be opened during the respiratory cycle, ∆P will be high and stress index slightly increased (B). With a modest loss of aeration, ∆P and stress index can be kept within acceptable ranges easily (C). In a lung where static hyperaeration is present already at end-expiration, such as in a patient where the lung is kept open with the use of an unnecessarily high PEEP, tidal hyperinflation can overlap to the static hyperaeration (D). V_T, tidal volume; Crs, compliance of the respiratory system; ∆P, driving pressure; PEEP, positive end-expiratory pressure.