IPAP = ventilation.
Higher settings increase the tidal volume, which lowers C02 levels.
EPAP isn't exactly PEEP but you can think of it that way. It's a lower amount of positive pressure keeping the lungs open. (or positive pressure for CHF... depending on the application). Usually set at 5 or 6... it won't change much.
Like everyone has said... settings change per ABG results.
Or pt tolerance. An IPAP of >20 and the pt might as well hang their head out the window going down the track at NASCAR.