In a prospective observational study, 30 deeply sedated and paralyzed ARDS patients ventilated in volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) modes on a Maquet Servo ventilator were studied. At inspiratory to expiratory (I:E) ratios of 1:2 and 1:1, the inspiratory rise time (Tslope) was adjusted from 5% to 15%, and 720 P–V loop images were analyzed. The mechanical power (MPtotal) was calculated geometrically based on the area of these loops. In VCV mode, increasing Tslope from 5% to 15% led to a significant increase in MPtotal by 0.8 J/min (at I:E 1:2) and by 0.1 J/min (at I:E 1:1). On the contrary, in the PCV mode, the extension of Tslope caused a decrease in MPtotal by 1.8 J/min (12.5% at I:E 1:2) and by 1 J/min (7% at I:E 1:1). No intrinsic PEEP detected. Adjusting Tslope changes MPtotal in opposite directions in both ventilation modes.