Fig. 4
From: Practical assessment of risk of VILI from ventilating power: a conceptual model
Innocuous Power (top panel) for comparison with two examples of similar total power (×) with nearly equal damaging potential (middle and lower panels). Each individual inflation cycle plots pressure on the vertical axis and time (an analog of inspired volume) on the horizontal axis for the example of constant flow. Damaging power (y) can be delivered by greater frequency of cycles with limited damaging energy (middle panel) or greater damaging energy per cycle delivered at a lower rate (lower panel). Note that whatever the inspiratory flow waveform, whether the same total power is damaging or not depends on both the threshold pressure (Pt) and frequency. All damaging elastic energy, \(W_{{{\text{Elastic}}}}\), is signified by the sum of all checked plus crosshatched areas. The damaging \(W_{{{\text{Drive}}}}\) component of \(W_{{{\text{Elastic}}}}\) omits the horizontally crosshatched area that corresponds to PEEP. Driving Power = \(W_{{{\text{Drive}}}}\) × frequency; Elastic power = \(W_{{{\text{elastic}}}}\) × frequency; Pt = pressure threshold boundary between safe and hazardous inflation energy