Lipopolysaccharide "two-hit" induced refractory hypoxemia acute respiratory distress model in rats.

To establish a stable and reliable model of refractory hypoxemia acute respiratory distress syndrome (ARDS) and examine its pathological mechanisms, a total of 144 healthy male Wistar rats were randomized into 4 groups: group I (saline control group), group II (LPS intravenous "single-hit" group), group III (LPS intratracheal "single-hit" group) and Group IV (LPS "two-hit" group). Rats were intravenously injected or intratracheally instilled with a large dose of LPS (10 mg/kg in 0.5 mL) to simulate a single attack of ARDS, or intraperitoneally injected with a small dose of LPS (1 mg/kg) followed by tracheal instillation with median dose of LPS (5 mg/kg) to establish a "two-hit" model. Rats in each group were monitored by arterial blood gas analysis and visual inspection for three consecutive days. Arterial blood gas values, lung wet/dry weight ratio and pathological pulmonary changes were analyzed to determine the effects of each ALI/ARDS model. Concentrations of TNF-alpha, IL-1 and IL-10 in the bronchoalveolar lavage fluid (BALF) and blood plasma were measured by using enzyme-linked immunosorbent assays (ELISA). Our results showed that single LPS-stimulation, whether through intravenous injection or tracheal instillation, could only induce ALI and temporary hypoxemia in rats. A two-hit LPS stimulation induces prolonged hypoxemia and specific pulmonary injury in rats, and is therefore a more ideal approximation of ARDS in the animal model. The pathogenesis of LPS two-hit-induced ARDS is associated with an uncontrolled systemic inflammatory response and inflammatory injury. It is concluded that the rat ARDS model produced by our LPS two-hit method is more stable and reliable than previous models, and closer to the diagnostic criteria of ARDS, and better mimics the pathological process of ARDS.