Assisted Ventilation: Pressure Support and Bilevel Ventilation Modes

Abstract

In contrast to fully controlled mechanical ventilation, during assisted ventilation both the ventilator and respiratory muscles provide pressure to move air into the lungs. Pressure support ventilation (PSV) is the mode most frequently used during assisted mechanical ventilation. It is a mode of ventilation limited by pressure and cycled by flow. PSV unloads the respiratory pump and allows the patient to have some control over respiratory rate, tidal volume, and inspiratory flow. However, given that the same ventilator pressure is delivered for every breath, it also imposes the risk of under- and over-assistance. Bilevel ventilation is a pressure-cycled, time-controlled, intermittent mandatory ventilation which allows unrestricted spontaneous breathing at any time using an active exhalation valve. The ventilator delivers continuous positive airway pressure (CPAP) at two set levels including high CPAP level (P-high) and low CPAP level (P-low). In this chapter we discuss how to carefully set the PSV to avoid harm together with physiological and clinical consequences of using bilevel modes during assisted ventilation.