ACUTE RESPIRATORY DISTRESS INDUCED BY REPEATED SALINE LAVAGE PROVIDES STABLE EXPERIMENTAL CONDITIONS FOR 24 HOURS IN PIGS

Abstract

Surfactant depletion is most often used to study acute respiratory failure in animal models. Because model stability is often criticized, the authors tested the following hypotheses: Repeated pulmonary lavage with normal saline provides stable experimental conditions for 24 hours with a PaO₂/FiO₂ ratio < 300 mm Hg. Lung injury was induced by bilateral pulmonary lavages in 8 female pigs (51.5 ± 4.8 kg). The animals were ventilated for 24 hours (PEEP: 5 cm H₂O; tidal volume: 6 mL/kg; respiratory rate: 30/min). After 24 hours the animals were euthanized. For histopathology slides from all pulmonary lobes were obtained. Supernatant of the bronchoalveolar fluid collected before induction of acute respiratory distress syndrome (ARDS) and after 24 hours was analyzed. A total of 19 ± 6 lavages were needed to induce ARDS. PaO₂/FiO₂ ratio and pulmonary shunt fraction remained significantly deteriorated compared to baseline values after 24 hours (P <. 01). Slight to moderate histopathologic changes were detected. Significant increases of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were observed after 24 hours (P <. 01). The presented surfactant depletion–based lung injury model was associated with increased pulmonary inflammation and fulfilled the criteria of acute ling injury (ALI) for 24 hours.

Keywords:

• animal model
• ARDS
• inflammation
• lung protection
• PEEP
• pigs
• saline lavage
• tidal volume