Emergent non-invasive ventilation monitoring: Tidal expiratory flow limitation monitoring by the forced oscillation technique and its role in closed-loop ventilation

Many chronic obstructive pulmonary disease (COPD) patients present tidal expiratory flow limitation (EFLT), which is associated with the development of an intrinsic positive end-expiratory pressure (PEEP) and dyspnea. In COPD patients receiving non-invasive ventilation (NIV) an external positive is used to counteract the intrinsic PEEP (PEEPi) and abolish EFLT; therefore, assessing EFLT during NIV is crucial for tailoring PEEP to individual patients. The forced oscillation technique (FOT) is a simple and non-invasive method used to measure the mechanical properties of the respiratory system [1]. It consists in evaluating the mechanical response of the respiratory system to small amplitude pressure oscillations. FOT does not require patient cooperation, does not interfere with the spontaneous breathing of the patient or with ventilator cycling during mechanical ventilation, and it is suitable for the continuous and automatic measurement of the patient's respiratory mechanics. The abovementioned features, which contrast with conventional methods of measuring respiratory mechanics, make FOT attractive for monitoring patients receiving mechanical ventilation and for implementing closed-loop ventilation strategies. In this chapter, we will focus on the application of FOT for EFLT in COPD patients receiving NIV and on its application to the closed-loop titration of the applied PEEP.