Mechanical ventilators are commonly used to support critically ill patients; however, inappropriate ventilator settings might initiate or augment lung injury. To determine whether a large tidal volume (Vt) augments inflammatory responses and neutrophil sequestration in the lungs of rats receiving intratracheal lipopolysaccharides (LPS). Rats received intratracheal instillation of LPS (0.5 mg/kg) followed by 4 h of mechanical ventilation (MV) at 60 strokes per min with a Vt of 10 mL/kg as control MV, or 30 strokes per min with a Vt of 20 mL/kg of body weight as high-volume MV (HMV). In addition, monoclonal antibodies against rat intercellular adhesion molecule 1 (ICAM-1) or immunoglobulin G (50 mg/kg) were administered 30 min before LPS instillation and MV. Our study demonstrates that HMV enhances pulmonary permeability and induces neutrophil recruitment into the alveolar space and pulmonary edema. Intratracheal instillation of LPS caused marked lung injury, neutrophil recruitment, and production of cytokines and chemokines. Combining LPS instillation and HMV synergistically upregulated interleukin 1β (IL-1β) production and neutrophil sequestration in lung tissues. The ICAM-1 expression in lung tissues was responsible for the synergistic effects of neutrophil sequestration. Synergistic upregulation of IL-1β production and neutrophil sequestration was attenuated by blocking ICAM-1 by neutralizing antibody pretreatment. High Vt MV in LPS-injured lung causes synergistic production of IL-1β and sequestration of neutrophil via ICAM-1-dependent effects.
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