We studied endotracheal suctioning-induced alveolar derecruitment and its prevention in nine patients with acute lung injury. Changes in end-expiratory lung volume measured by inductive plethysmography, positive end-expiratory pressure-induced alveolar recruitment assessed by pressure-volume curves, oxygen saturation, and respiratory mechanics were recorded. Suctioning was performed after disconnection from the ventilator, through the swivel adapter of the catheter mount, with a closed system, and with the two latter techniques while performing recruitment maneuvers during suctioning (40 cm H2O pressure-supported breaths). End-expiratory lung volume after disconnection fell more than with all other techniques (-1,466 +/- 586, -733 +/- 406, -531 +/- 228, -168 +/- 176, and -284 +/- 317 ml after disconnection, through the swivel adapter, with the closed system, and with the two latter techniques with pressure-supported breaths, respectively, p < 0.001), and was not fully recovered 1 minute after suctioning. Recruitment decreased after disconnection and using the swivel adapter (-104 +/- 31 and -63 +/- 25 ml, respectively), was unchanged with the closed system (-1 +/- 10 ml), and increased when performing recruitment maneuvers during suctioning (71 +/- 37 and 60 +/- 30 ml) (p < 0.001). Changes in alveolar recruitment correlated with changes in lung volume (rho = 0.88, p < 0.001) and compliance (rho = 0.9, p < 0.001). Oxygenation paralleled lung volume changes. Suctioning-induced lung derecruitment in acute lung injury can be prevented by performing recruitment maneuvers during suctioning and minimized by avoiding disconnection.