Plateau pressures are obtained by doing an inspiratory hold on the ventilator. When you do this the ventilator gives you the peak alveolar pressure. Ideally this number should be Respiratory...
25 is the highest that you will see for the most part. To need to be on 25 of PEEP the pts lungs are usually very non-compliant because of ARDS, and the risk for barotrauma is high with these...