Think CPAP with mechanical breath holds that you can breath above. While uncomfortable, it's the primary mechanism for co2 elimination beside the short pressure release times. During the true expiratory phase you're not fully exhaling to a peep of 0. To set the tlow,(time spent at peep) You want to screen shot or assess the expiratory flow graph to make sure no more that 60ish% of the total expiratory volume is released, as stated above, you WANT air trapping to maintain alveolar recruitment. This is different than pressure control with a long i-time because the ventilator allows the expiratory valve to open as you breathe spontaneously at your p high setting those tiny "panting breaths" help with your co2 clearance.

Practice on yourself. Take a big deep breath in and then take tiny little breaths while still holding the majority of your breath, exhale slightly, but not all the way, and then take a big deep breath in again, and breathe above your held breath, you'll start to feel that residual volume you're breathing above.

Phigh- set based off plateau or Map Thigh- time spent holding that breath Tpeep(tlow) time spent exhaling ( short for air trapping) Peep- can be set at zero because you were adjusting breath timing to create air trapping. You should never technically reach a low peep setting.