VENTILATION STRATEGIES AFFECT SURFACTANT AGGREGATE CONVERSION IN ACUTE LUNG INJURY

This study evaluated the effects of varying tidal volumes (VT) and pos itive end-expiratory pressure (PEEP) levels on surfactant aggregate co nversion and lung function in an animal model of lung injury induced b y N-nitroso-N-methylurethane. Lung-injured adult rabbits were initiall y ventilated using a VT Of 10 ml/kg (VT10), a respiratory rate of 30 b reaths/min (RR30), and a PEEP of 3.5 cm H2O. A trace dose of radiolabe led rabbit large surfactant aggregates was instilled after the onset o f ventilation, and animals were then ventilated at different ventilato r settings for 1 h. Ventilation strategies involving a lower VT (VT5, RR60) resulted in significantly superior oxygenation and lower surfact ant aggregate conversion rates than strategies involving a higher VT ( [VT10, RR30], [VT15, RR20], p < 0.05). Increasing the PEEP level to 8. 0 cm H2O improved oxgenation, but it was sustained only with a low VT (VT5, RR60), and deteriorated with a high VT (VT10, RR30). Varying VT but not PEEP levels resulted in significant changes in surfactant aggr egate conversion. We conclude that increased surfactant aggregate conv ersion resulting from suboptimal ventilation of injured lungs may play an important role in the pathophysiology of ventilation-induced lung dysfunction in acute lung injury.