Pressure support ventilation (PSV). With this technique, the ventilator delivers a set amount of positive pressure into the lungs each time the patient initiates a breath. The positive pressure continues throughout inspiration and ends when the expira tory phase of ventilation begins. (The expiratory phase actually starts when the patient's inspiratory flow rate falls to 25% of his peak inspiratory flow rate.10) With PSV, the patient controls the length and depth of each respiration and is able to breathe at his own rate. When the machine is set to deliver the maximal level of PS, the patient should be able to breathe comfortably at a respiratory rate of 20 or less, without using accessory muscles, while achieving a tidal volume of at least 8 – 12 mL/kg.