The plateau pressure is measured after a breath has been delivered to the patient and before exhalation begins. Exhalation is prevented by the ventilator for a brief moment (0.5 to 1.5 sec). To obtain this measurement, the ventilator operator normally selects a control marked "inflation hold" or "inspiratory pause".

 

Plateau pressure measurement is like holding the breath at the end of inspiration. At the point of breath holding, the pressures inside the alveoli and mouth are equal (no gas flow). However, the relaxation of the respiratory muscles and the elastic recoil of the lung tissues are exerting force on the inflated lungs. This creates a positive pressure and reads on the manometer as a positive pressure.

 

Because it occurs during a breath hold, or pause, the reading is stable; it "plateaus" at a certain value. The plateau pressure reflects the effect of the elastic recoil on the gas volume inside the alveoli and any pressure exerted by the volume in the ventilator circuit that is acted upon by the recoil of the plastic circuit.