- During the 12-36 hour(ideally 12-24 hr) period, PaO2/FIO2 must remain < 200 mm Hg for an ABG obtained 30 minutes after placement on the following specific ventilator settings: Volume A/C, Tidal volume = 6 ml/kg PBW, Plateau pressure ≤ 30 cmH2O, Inspiratory time ≤ 1 second, PEEP ≥ 10 cmH2O, FIO2 ≥ 0.5, Ventilator rate to keep PaCO2 = 35-60 mmHg