Volume 140, Issue 2, Pages 286-290 (August 2011) Point: Is Pressure Assist-Control Preferred Over Volume Assist-Control Mode for Lung Protective Ventilation in Patients With ARDS? Yes  John J. Marini, MD  CHEST  Volume 140, Issue 2, Pages 286-290 (August 2011) DOI: 10.1378/chest.11-1060 Copyright © 2011 The American College of Chest Physicians Terms and Conditions

Figure 1 Profiles of airway pressure and flow for VACV with constant inspiratory flow and PACV. Both are delivered with the same tidal volume (Vt) and inspiratory time. Note the near-constant airway pressure of PACV that results in a decelerating flow profile, which ends in a brief end-inspiratory segment of no flow. PACV = pressure assist-control ventilation; VACV = volume assist-control ventilation. CHEST 2011 140, 286-290DOI: (10.1378/chest.11-1060) Copyright © 2011 The American College of Chest Physicians Terms and Conditions

Figure 2 Pure mechanical injury produced by high driving pressure and low positive end-expiratory pressure. In this anesthetized animal ventilated in the supine position, there appeared a sharp separation between severely injured dependent lung tissues and relatively uninjured lung tissues in nondependent zones exposed to higher transpulmonary pressure. A, Ventral aspect. B, Dorsal aspect. Injury proceeded stepwise from dependent to nondependent regions (arrows). This apparent paradox may be explained best by amplified tissue strains experienced at the boundary of open and closed lung units. CHEST 2011 140, 286-290DOI: (10.1378/chest.11-1060) Copyright © 2011 The American College of Chest Physicians Terms and Conditions

Figure 3 Theoretical relationships between aerated FRC, Vt, and their “strain ratio” (Vt/FRC) at baseline (Base), and after injury increases the volume of consolidated (nonaerated) lung at the expense of FRC during VACV or PACV with unadjusted settings and the same levels of positive end-expiratory pressure. Note that the strain ratio increases considerably and the driving pressure rises moderately in VACV because aerated FRC falls and peak pressure elevates with Vt held constant. The strain ratio rises less, if at all, with PACV, since Vt and driving pressure both decline in parallel with worsening compliance and declining FRC. FRC = functional residual capacity. See Figure 1 legend for expansion of other abbreviations. CHEST 2011 140, 286-290DOI: (10.1378/chest.11-1060) Copyright © 2011 The American College of Chest Physicians Terms and Conditions