Fig. 2
The evolution of ventilator-induced lung injury (VILI) can be described as an ever-shrinking baby lung known as a VILI vortex [45]. The ‘patient’ with mild ARDS with mostly open lung tissue (pink) and a lesser amount of collapsed tissue (red) is placed on ARDSNet LVT ventilation. The LVT strategy is designed to shield the ‘baby lung’ from overdistension. However, this strategy using low VT and low airway pressures allows acutely injured tissue to continually collapse pushing it into the VILI vortex. As normal tissue progressively shrinks (pink → red), lung pathogenesis moves from mild-to-moderate ARDS. If unchecked, lung injury will progress into severe ARDS, at which point rescue methods such as extracorporeal membrane oxygenation (ECMO) may be necessary. ARDS causes the lung to become time and pressure dependent. This means that it will take more time for alveoli to open and less time for them to collapse at any given airway pressure. Thus, inspiratory and expiratory time can be used to accelerate alveolar opening and to minimize alveolar collapse. Using the ARDSNet approach, the short time at inspiration is not adequate to open collapsed alveoli, while the extended time at expiration will not prevent alveolar collapse (upper left ARDSNet LVT, Pressure/Time curve on the ventilator monitor). The open lung approach (OLA) using higher PEEP with and without recruitment maneuvers to rapidly (seconds or minutes) open the collapsed ARDS lung has not been successful at reducing ARDS-related mortality. Our group and others have shown the ability of inspiratory and expiratory duration to open and stabilize alveoli. Multiple studies using time-controlled ventilation strategies have confirmed that an extended inspiratory time will progressively recruit alveoli and a very brief expiratory time will prevent re-collapse [63, 66, 68, 71,72,73,74,75,76,77,78,79,80,81,82,83, 85, 86, 90]. An ventilator method to rapidly stabilize the lung (Center, Lung Stabilization, Pressure/Time curve on the ventilator monitor) using a very brief expiratory duration (Fig. 4B, Release Phase) has been shown to stabilize alveoli (Fig. 6, APRV 75%) and prevent progressive lung collapse pulling the lung from the Vortex. Once removed from the vortex, the collapsed tissue can be reopened slowly (gradual lung recruitment) over hours or day depending on the level of lung pathophysiology (Fig. 4B, CPAP Phase) [63, 66, 68, 71,72,73,74,75,76,77,78,79,80,81,82,83, 85, 86, 90]