Objective: Repeated derecruitments of previously recruited lungs can exacerbate lung injuries during mechanical ventilation. The aim of this study was to assess lung injury associated with repeated derecruitments and to assess whether this type of injury could be attenuated by recruitment maneuvers.
Design: Prospective, randomized, experimental animal study.
Setting: University laboratory.
Subjects: New Zealand White rabbits.
Interventions: Twenty-one rabbits were ventilated in pressure-controlled mode with constant tidal volume (10 mL/kg). After lung injury was induced by repeated saline lavage, positive end-expiratory pressure (PEEP) at a lower inflection point was applied for 3 hrs. The control group (n = 7) received ventilation with the same PEEP for 3 hrs without derecruitments. In the derecruitment group (n = 7), derecruitment was repeatedly induced by intentional disconnection of the ventilatory circuit for 1 min every 10 mins for 3 hrs. In the recruitment maneuver group (n = 7), continuous positive airway pressure of 30 cm H2O was applied for 30 secs after each derecruitment.
Measurements and main results: After PEEP levels were increased to lower the inflection point value, Pao2 increased to >500 mm Hg in all groups. Increased Pao2 persisted at >450 mm Hg in the control and recruitment maneuver groups, whereas progressive declines in arterial oxygen levels were observed in the derecruitment group (median, 381.1 mm Hg [interquartile range, 350.1-466.7 mm Hg] at 2 hrs and 318.2 mm Hg [214.3-414.9 mm Hg] at 3 hrs, p < .05 compared with other groups). Histologically, there was significantly increased hyaline membrane formation in alveolar ducts in the derecruitment group compared with the control group (p = .005). Also, significantly more membranous and respiratory bronchiolar injuries were observed in the derecruitment group compared with the control and recruitment maneuver group (p < .005).
Conclusions: These findings suggest that repeated derecruitments could induce lung injuries during mechanical ventilation, and recruitment maneuvers may attenuate derecruitment-associated lung injuries.