Mechanical ventilators are set to deliver a constant volume (volume cycled), a constant pressure (pressure cycled), or a combination of both with each breath. Modes of ventilation that maintain a minimum respiratory rate regardless of whether or not the patient initiates a spontaneous breath are referred to as assist-control (A/C). Because pressures and volumes are directly linked by the pressure-volume curve, any given volume will correspond to a specific pressure, and vice versa, regardless of whether the ventilator is pressure or volume cycled.Adjustable ventilator settings differ with mode but include respiratory rate, tidal volume, trigger sensitivity, flow rate, waveform, and inspiratory/expiratory (I/E) ratio.