Your first choice in operating a mechanical ventilator is to provide the patient with either a specified volume of air (volume control or volume-cycled ventilation) or a specified pressure of air (pressure control or pressure-cycled ventilation). Remember that pressure and volume have an inverse relationship. In volume control, when you set a volume and a respiratory rate, pressure will vary based on the patient’s respiratory system compliance. In pressure control, when you specify a pressure, volume will vary, based on the patient’s respiratory system compliance. In general, volume control is used more often than pressure control.