Morphometric effects of the recruitment maneuver on saline-lavaged canine lungs - A computed tomographic analysis

Background: In the face of widespread use of lung-protective, low-volume ventilation in patients with acute lung injury, interest in the recruitment maneuver (RM) is growing. Little is known about lung-morphometric effects of the RM as compared with positive end-expiratory pressure (PEEP) titration (PT) without the RM. Methods: RM was defined as a stepwise change in PEEP from baseline to 10, 20, 30, and 20 cm H(2)O every 30 s, after which PEEP was reset at the lower inflection point + 2 cm H(2)O. For PT, PEEP was simply increased from baseline to the lower inflection point + 2 cm. H(2)O. Both maneuvers were performed in 10 lung-lavaged dogs. Computed tomography of the lung was performed before and 30 s and 30 min after the maneuver. Results: Thirty seconds after the maneuver, the decrease in the amount of nonaerated plus poorly aerated lung was greater and decreases in Hounsfield units in the caudal and dorsal lung regions were greater with the RM than with the PT. The hyperaerated lung volume after the RM tended to be greater than that after the PT. At 30 s and 30 min after the maneuver, gas plus tissue volume, gas-only volume, and gas-tissue ratio of the lung were greater with the RM than with the PT. At both time points after the maneuver, the coefficient of variation of regional Hounsfield units, an index of regional heterogeneity of aeration, was lower with the RM than with the PT. Conclusions: Compared with PT, the RM resulted in a greater lung volume, better aeration of the most dependent lung, and less regional heterogeneity of aeration. However, the RM tended to induce a greater increase in hyperaerated lung volume than did the PT.