Mechanical ventilation with high positive end-expiratory pressure and small driving pressure amplitude is as effective as high-frequency oscillatory ventilation to preserve the function of exogenous surfactant in lung-lavaged rats

Objective: To demonstrate that under well-defined conditions, pressure-cont rolled ventilators (PCV) allow settings that are as good as high-frequency oscillatory ventilators (HFOV) at preserving the function of exogenous surf actant in lung-lavaged rats. Design: Experimental, comparative study. Setting: Research laboratory of a large university. Subjects: Sixteen adult male Sprague-Dawley rats (280-310 g). Interventions: Lung injury was induced by repeated lavage. After last lavag e, all animals received exogenous surfactant and were then randomly assigne d to two groups (n = 8 per group). The first group received PCV with small pressure amplitudes and high positive end-expiratory pressure. The second g roup received HFOV. In both groups, an opening maneuver was performed by in creasing airway pressure to improve PaO2/FIO2 to greater than or equal to 5 00 torr. Measurements and Main Results: Blood gases were measured every 30 mins for 3 hrs. Airway pressures were measured with a tip catheter pressure transduc er. At the end of the study period, a pressure-volume curve was recorded an d a broncho-alveolar lavage was performed to determine protein content and surfactant composition. The results showed that arterial oxygenation in bot h groups could be kept >500 torr during the 3-hr study period by using a me an airway pressure of 13 +/- 3 cm H2O in PCV and 13 +/- 2 cm H2O in HFOV. F urther, there were no differences in the Gruenwald index, protein influx, o r ratio of small to large aggregates between the study groups. Conclusion: PCV with sufficient level of positive end-expiratory pressure a nd small driving pressure amplitudes is as effective as HFOV to maintain op timal gas exchange, to improve lung mechanics, and to prevent protein influ x and conversion of large into small aggregates after exogenous surfactant therapy in lung-lavaged rats.