Fig. 1.
Driving pressure (ΔP) is calculated as the difference between plateau pressure (Pplat) and positive end-expiratory pressure (PEEP). Driving pressure is composed of two pressures: that distributed to the lung itself, the transpulmonary pressure (ΔPL), and that applied to the chest wall (ΔPcw). Rearrangement of the standard respiratory system compliance (CRS) equation leads to driving pressure as equal to the tidal volume (VT) divided by CRS. Strain is a measure of material deformation relative to its original state. For example, the linear displacement of a spring (ΔL) relative to its rest length (Lo), or equivalently the ratio of VT to residual functional capacity (FRC). As CRS changes in proportion to FCR, i.e FRC=k × CRS, VT/CRS is an approximation of tidal volume normalized to FRC, and ΔP is proportional to lung strain. TLC=Total lung capacity. VL = lung volume.