I. Introduction A. Background Lung units which participate in gas exchange are known as 'recruited' lung. Patients with lung injury suffer from a proportion of units which do not participate in gas exchange (i.e. the derecruited state), at times resulting in impaired gas exchange. Derecruitment of alveoli may also cause intrapulmonary shunting and worsen lung injury through atelectotrauma7. Outcomes in acute respiratory distress syndrome have improved significantly Is this really true? since clinicians have begun to employ lung protective strategies, including low-tidal volume ventilation and permissive hypercapnea8, 9. However, low-tidal volume ventilation has been recognized to decrease recruited lung volume, a phenomenon which persists despite the aggressive positive end-expiratory pressure (PEEP) strategy employed in ARDSNet studies4. Atelectasis associated with low-tidal volume ventilation is relieved through the use of so-called sign breaths, or recruitment breaths10. Further, the proportion of lung remaining in the derecruited state may contribute to the morbidity and mortality associated with acute respiratory distress syndrome (ARDS)11. In adults, several strategies have been utilized to recruit the lung: sustained inflation (SI) and the maximal recruitment strategy. The so-called open lung approach (OLA) includes an SI followed by the setting of PEEP to the measured lower inflection point of the PV curve. An alternative approach to setting PEEP is a decremental PEEP titration, which includes the sequential lowering of PEEP until a predetermined decrement in PaO2 or SaO2 occurs. Studies which have not included a strategy for maintaining lung recruitment following a recruitment maneuver have all been studied.