Pressure limiting allows pressure to rise to a certain value but not exceed it. The ventilator pushes a volume of gas into the ventilator CIrcuit, which causes the pressure in the circuit to rise. To prevent excessive pressure from entering the patient's lungs, the operator sets a control sometimes labeled a high pressure limit. When the ventilator reaches the high pressure limit, excess pressure is vented through a spring-loaded pressure­release, or pop-off valve.

 

Stiff lungs require more pressure to inflate. With stiff lungs the pressure limit is reached before the end of the breath is reached, and no more volume is delivered.

 

Infant ventilators often pressure limit the inspiratory phase but time cycle inspiration. Other examples of pressure-limiting modes are pressure support and pressure control.