Pulmonary surfactant is altered during mechanical ventilation of isolated rat lung

Objective: To test the hypothesis that the lung injury induced by certain m echanical ventilation strategies is associated with changes in the pulmonar y surfactant system. Design: Analysis of the pulmonary surfactant system from isolated rat lungs after one of four different ventilatory strategies. Setting: A research laboratory at a university. Subjects: A total of 45 Sprague-Dawley rats. Interventions: Isolated lungs were randomized to either no ventilation (0-T IME) or to ventilation at 40 breaths/min in a humidified 37 degrees C chamb er for either 30 mins or 120 mins with one of the following four strategies : a) control (CON, 7 mL/kg, 3 cm H2O positive end-expiratory pressure); b) medium volume, zero end-expiratory pressure (MVZP, 15 mL/kg, 0 cm H2O end-e xpiratory pressure); c) medium volume, high positive end-expiratory pressur e (MVHP, 15 mL/kg, 9 cm H2O positive end-expiratory pressure); and d) high volume, zero end-expiratory pressure (HVZP, 40 mL/kg, 0 cm H2O end-expirato ry pressure). Measurements: Pressure-volume curves were determined before and after the v entilation period, after which the lungs were lavaged for surfactant analys is. Main Results: Compared with 0-TIME, 30 mins of ventilation with the HVZP st rategy or 120 mins of ventilation with CON and MVZP strategies caused a sig nificant decrease in compliance. Groups showing a decreased compliance had significant increases in the amount of surfactant, surfactant large aggrega tes, and total lavage protein compared with 0-TIME. Conclusions: A short period of injurious mechanical ventilation can cause a decrease in lung compliance that is associated with a large influx of prot eins into the alveolar space and with alterations of the pulmonary surfacta nt system. The changes of surfactant in these experiments are different fro m those seen in acute lung injury, indicating that they may represent an in itial response to mechanical ventilation.