difference between peak and plateau pressures
The peak pressure is the pressure measured by the ventilator in the major airways, and it strongly reflects airways resistance. For example, in acute severe asthma, there is a large gradient between the peak pressure (high) and the plateau pressure (normal). In pressure controlled ventilation, the pressure limit is (usually) the plateau pressure due to the dispersion of gas in inspiration.
The plateau pressure is the pressure applied (in positive pressure ventilation) to the small airways and alveoli. It is believed that control of the plateau pressure is important, as excessive stretch of alveoli has been implicated as the cause of ventilator induced lung injury.