The standard of care for mechanical ventilation of the patient who has acute lung injury remains volume control ventilation at 6 mL/kg. Despite this fact, clinicians often employ pressure control ventilation and adaptive pressure control ventilation in an attempt to improve synchrony and limit the possibility for overdistension. Adaptive pressure control uses pressure control breaths to guarantee a minimum delivered tidal volume. Other techniques (such as adaptive support ventilation) use pressure-limited breaths, switching between time and flow cycling based on patient effort. Neither of these techniques has been compared with volume control in a randomized setting. Understanding operation of these techniques is essential for determining any impact on outcome or ventilator induced lung injury.