Comparison of exogenous surfactant therapy, mechanical ventilation with high end-expiratory pressure and partial liquid ventilation in a model of acute lung injury

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 mechanicall y with 100% oxygen and a PEEP of 6 cm H2O, and acute lung injury was induce d by repeated lung lavage to obtain a Pa-O2 value < 13 kPa. Animals were th en allocated randomly (n = 12 in each group) to receive exogenous surfactan t therapy, ventilation with high PEEP (18 cm H2O), partial liquid ventilati on or ventilation with low PEEP (8 cm H2O) (ventilated controls). Blood-gas values were measured hourly. At the end of the 4-h study, in six animals p er group, pressure-volume curves were constructed and bronchoalveolar lavag e (BAL) was performed, whereas in the remaining animals lung injury was ass essed. In the ventilated control group, arterial oxygenation did not improv e and protein concentration of BAL and conversion of active to non-active s urfactant components increased significantly. In the three treatment groups , Pao, increased rapidly to > 50 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 surfa ctant components increased significantly in the partial liquid ventilation group and in the group ventilated with high PEEP. In the surfactant group a nd partial liquid ventilation groups, less lung injury was found compared w ith the ventilated control group and the group ventilated with high PEEP. W e conclude that although all three strategies improved Pa-O2 to > 50 kPa, t he impact on protein transfer into the alveoli, surfactant system and lung injury differed markedly.