Open lung ventilation improves gas exchange and attenuates secondary lung injury in a piglet model of meconium aspiration

Objective: Previous studies failed to show clear benefits of high-frequency ventilation compared with conventional positive pressure ventilation (PPV_CON) in experimental meconium aspiration syndrome. However, none of these studies applied an open lung ventilation strategy (OLC), which aims to reduce intrapulmonary shunt due to alveolar collapse. We hypothesized that, if combined with an open lung strategy, both high-frequency oscillatory ventilation (HFOV_OLC) and positive pressure ventilation (PPV_OLC) would improve gas exchange and attenuate ventilator-induced lung injury in experimental meconium aspiration syndrome. Design: Prospective, randomized animal study. Setting: Research laboratory of a large university. Subjects: Forty-two newborn piglets. Interventions: Thirty minutes after intratracheal meconium instillation, 36 newborn piglets were assigned to one of three ventilation groups - PPV_OLC, HFOV_OLC, or PPV _CON - and ventilated for 5 hrs. In both OLC groups, collapsed alveoli were actively recruited and thereafter stabilized using the lowest possible airway pressures. During PPV_CON, ventilator settings were adjusted to prevent critical hypoxia (PaO₂ <60 torr [8 kPa]). Six animals served as saline controls. Measurements and Main Results: Compared with the PPV_CON group, arterial oxygenation and lung mechanics were superior in both OLC groups and the saline controls. Analysis of the bronchoalveolar lavage fluid obtained after 5 hrs of ventilation showed increased myeloperoxidase activity in the PPV_CON group compared with both OLC groups and saline controls. Alveolar protein influx was not different between the groups. Histologic analysis revealed a higher lung injury score in the PPV_CON group compared with the PPV_OLC and the HFOV_OLC groups. Conclusions: Application of the OLC during PPV and HFOV is feasible in experimental meconium aspiration syndrome and results in superior oxygenation and less ventilator-induced lung injury compared with PPV_CON.