Fig. 4. Profiles of arterial oxygen tension (Pao²;  left ) and arterial carbon dioxide tension (Paco²;  right ) changes from the beginning (time 0) to 15 min after closed-circuit endotracheal suctioning in nine patients with acute lung injury. Closed-circuit endotracheal suctioning followed by a recruitment maneuver (  arrow ) was performed at two levels of negative pressure: −200 cm H²O (  gray lines ) and −400 cm H²O (  black lines ).  Gray arrows indicate the beginning of the recruitment maneuver. Pao²and Paco²were measured every second. Data are expressed as percentage of changes from baseline values.