Figure 252-2 A. Airway pressure and lung volume versus time profiles during pressure-control ventilation (PCV). All breaths are timer triggered, timer cycled, and pressure limited. Peak airway pressure is set by the operator, and tidal volume is a dependent variable. The profiles shown here display the pressure limit as slightly higher than pressure-control level. This need not be the case, but it is appropriate to set the pressure limit only slightly above the pressure-control level when using this mode of ventilation for management of the patient with barotrauma. B. Airway pressure and airway flow versus time profiles during pressure-support ventilation (PSV). All breaths are patient triggered and flow cycled. Inspiration is cycled off when the inspiratory flow drops below a predetermined threshold internally set in the ventilator circuit. In the example shown, the pressure limit is slightly greater than the pressure-support level. Since each can be set independently, this need not be the case. FRC, functional residual capacity.