Impact of the Type of Pressure Controlled Mode on Lung Protection in Mechanically Ventilated Patients With Spontaneous Breathing

Mechanical ventilation (MV) is a cornerstone of management of acute respiratory failure, but MV per se can provoke ventilator-induced lung injury (VILI), especially in acute respiratory distress syndrome (ARDS). Lung protective ventilation strategy has been proved to prevent VILI by using low tidal volume of 6-8 ml/kg of ideal body weight and limiting plateau pressure to less than 30 cmH2O. However, heavy sedation or even paralysis are frequently used to ensure the protective ventilation strategy, both of which are associated with respiratory muscles weakness. Maintaining of spontaneous breathing may decrease the need of sedative drug and improve gas exchange by promoting lung recruitment.

Pressure-targeted mode is the most frequent way of delivering after 48 hours of initiating MV. Three types of pressure-controlled mode are available in intubated patients: Biphasic Intermittent Positive Airway Pressure (BIPAP), Airway Pressure Release Ventilation (APRV), and Pressure-Assist Controlled Ventilation (also called BIPAPassist). They are based on pressure regulation but have the difference in terms of synchronization between the patient and the ventilator. The different working principle of these modes may result in different breathing pattern and consequently different in tidal volume and transpulmonary pressure, which may be potentially harmful. The investigators bench study with a lung model demonstrated higher tidal volume and transpulmonary pressure with the BIPAPassist over APRV despite similar pressure settings and patient's simulated effort. However, the impact of each mode on the delivered tidal volume and the transpulmonary pressure in spontaneously breathing mechanically ventilated patients is currently unknown. Their hypothesis is that when the investigators compare the three pressure-controlled modes, the asynchronous mode (APRV) will result in more protective ventilation strategy over the two other modes (BIPAP and BIPAPassist).