System and methods for ventilating a patient are provided. In one embodiment, the method comprises steps of placing a ventilator in a mode capable of delivering respiratory gas based on at least one fixed parameter and at least one variable parameter, the fixed parameters being tidal volume and peak airway pressure and the variable parameter being PEEP, identifying a first level for the PEEP, configuring the ventilator to deliver the respiratory gas at the peak airway pressure and the PEEP to achieve the tidal volume, monitoring respiratory gas flow over time to measure tidal volume, setting a second level for the PEEP based on the measured tidal volume, automatically adjusting the PEEP to the second level relative to the peak airway pressure and repeating the steps of configuring, monitoring, setting and automatically adjusting to achieve the ventilation.