Repetitive high-pressure recruitment maneuvers required to maximally recruit lung in a sheep model of acute respiratory distress syndrome

Objective: To compare the effects of two different recruitment maneuvers re peated multiple times on gas exchange lung injury, hemodynamic, and lung me chanics. Design: Randomized prospective comparison. Settings: Animal research laboratory. Subject. Nineteen fasted Hampshire sheep. Interventions: In 15 27-kg sheep with saline lavage lung injury, we compare d the effects of two recruitment maneuvers: 40 cm H2O continuous positive a irway pressure for 60 secs and 40 cm H2O positive end-expiratory pressure w ith 20 cm H2O pressure control, rate 10 breaths/min, inspiratory to expirat ory ratio 1:1 for 2 mins. Each recruitment maneuver was repeated four times , every 30 mins after a 30-sec ventilator disconnection. An additional grou p received no recruitment maneuvers. Animals were assigned randomly to the three groups and ventilated with 20 cm H2O positive end-expiratory pressure , pressure control 15 cm H2O, rate 20 breaths/min, inspiratory to expirator y ratio 1:1, and FIO2 1.0 between recruitment maneuver periods. Measurements and Main Results. Significant and marked increases in PaO2 wer e observed in the pressure control recruitment maneuver group but only afte r the second recruitment maneuver. In both the control group and continuous positive airway pressure groups, PaO2 did not significantly increase after any recruitment maneuver compared with baseline injury. There was a signif icant decrease in cardiac output immediately after some continuous positive airway pressure recruitment maneuvers and a significant increase in mean p ulmonary artery pressure in both continuous positive airway pressure and pr essure control groups immediately after recruitment maneuvers, but these ch anges resolved within 10 mins. There were no marked histologic differences between groups and no volutrauma. Conclusion: In this model, maximal lung recruitment was obtained with 40 cm H2O positive end-expiratory pressure and 20 cm H2O pressure control applie d repetitively every 30 mins for 2 mins without physiologic or histologic h arm. Multiple recruitment maneuvers in some animals were required for maxim um effect.