We have compared three treatment strategies, that aim to prevent repetitive alveolar collapse, for their effect on gas exchange, lung mechanics, lung injury, protein transfer into the alveoli and surfactant system, in a model of acute lung injury. In adult rats, the lungs were ventilated mechanically with 100% oxygen and a PEEP of 6 cm H 2 O, and acute lung injury was induced by repeated lung lavage to obtain a Pa O 2 value Ͻ13 kPa. Animals were then allocated randomly (nϭ12 in each group) to

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... ceive exogenous surfactant therapy, ventilation with high PEEP (18 cm H 2 O), partial liquid ventilation or ventilation with low PEEP (8 cm H 2 O) (ventilated controls). Blood-gas values were measured hourly. At the end of the 4-h study, in six animals per group, pressure-volume curves were constructed and bronchoalveolar lavage (BAL) was performed, whereas in the remaining animals lung injury was assessed. In the ventilated control group, arterial oxygenation did not improve and protein concentration of BAL and conversion of active to non-active surfactant components increased significantly. In the three treatment groups, Pa O 2 increased rapidly to Ͼ50 kPa and remained stable over the next 4 h. The protein concentration of BAL fluid increased significantly only in the partial liquid ventilation group. Conversion of active to non-active surfactant components increased significantly in the partial liquid ventilation group and in the group ventilated with high PEEP. In the surfactant group and partial liquid ventilation groups, less lung injury was found compared with the ventilated control group and the group ventilated with high PEEP. We conclude that although all three strategies improved Pa O 2 to Ͼ50 kPa, the impact on protein transfer into the alveoli, surfactant system and lung injury differed markedly. Br J Anaesth 1999; 82: 81-6