At surfactant deficiency, application of "the open lung concept" prevents protein leakage and attenuates changes in lung mechanics

Objective: To evaluate whether mechanical ventilation using "the open lung concept" during surfactant depletion can attenuate the deterioration in pulmonary function. Design. Experimental, comparative study. Setting: Research laboratory of a large university. Subjects: Eighteen adult male Sprague-Dawley rats, weighing 280-340 g. Interventions: Twelve rats were anesthetized, mechanically ventilated with 100% oxygen, and randomly divided into two groups (n = 6 each). The open lung group underwent six saline lavages at different ventilator settings that prevented alveolar collapse. The settings (expressed as frequency/peak inspiratory pressure/positive end-expiratory pressure/inspiratory:expiratory ratio) were 30/26/6/1:2 during the first lavage, 100/27/10/1:1 during the next two lavages, and 100/33/15/1:1 during the last three; lavages and during the remaining ventilation period. The ventilated control group underwent six saline lavages with settings at 30/26/6/1:2. After the lavages, peak inspiratory pressure and positive end-expiratory pressure were increased in this group by 2 cm H2O each for the remaining study period. An additional group of six animals were killed immediately after induction of anesthesia and served as healthy controls. Blood gases were measured before lavage, immediately after the last lavage, and thereafter hourly. At the end of the 4-hr study period, we constructed pressure-volume curves from which we determined total lung capacity at a distending pressure of 35 cm H2O (TLC35). Subsequently, total lung volume at a distending pressure of 5 cm H2O (V-5) was determined, followed by bronchoalveolar lavage. Results: In the ventilated control group, PaO2, V-5, and TLC35 were significantly decreased and protein concentration of bronchoalveolar lavage was significantly increased compared with the healthy control group. In the open lung group, Pao, did not decrease after the lavage procedure, and V-5, TLC35, and the protein concentration of bronchoalveolar ravage were comparable with the healthy controls. Conclusion: We conclude that application of the open lung concept during surfactant depletion attenuates deterioration in pulmonary function.