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Background:Sepsis is a major cause of mortality in Intensive Care Units.Anesthetic dose isoflurane and 100％ oxygen were proved to be beneficial in sepsis;however,their application in septic patients is limited because long-term hyperoxia may induce oxygen toxicity and anesthetic dose isoflurane has potential adverse consequences.This study was scheduled to find the optimal combination ofisoflurane and oxygen in protecting experimental sepsis and its mechanisms.Methods:The effects of combined therapy with isoflurane and oxygen on lung injury and sepsis were determined in animal models of sepsis induced by cecal ligation and puncture (CLP) or intraperitoneal injection of lipopolysaccharide (LPS) or zymosan.Mouse RAW264.7 cells or human peripheral blood mononuclear cells (PBMCs) were treated by LPS to probe mechanisms.The nuclear factor kappa B (NF-κB) signaling molecules were examined by West blot and cellular immunohistochemistry.Results:The 0.5 minimum alveolar concentration (MAC) isoflurane in 60％ oxygen was the best combination of oxygen and isoflurane for reducing mortality in experimental sepsis induced by CLE intraperitoneal injection of LPS,or zymosan.The 0.5 MAC isoflurane in 60％ oxygen inhibited proinflammatory cytokines in peritoneal lavage fluids (tumor necrosis factor-alpha [TNF-α]:149.3 vs.229.7 pg/ml,interleukin [IL]-1β:12.5 vs.20.6 pg/ml,IL-6:86.1 vs.116.1 pg/ml,and high-mobility group protein 1 [HMGB1]:323.7 vs.449.3 ng/ml;all P ＜ 0.05) and serum (TNF-α:302.7 vs.450.7 pg/ml,IL-1β:51.7 vs.96.7 pg/ml,IL-6:390.4 vs.722.5 pg/ml,and HMGB1:592.2 vs.985.4 ng/ml;all P ＜ 0.05) in septic animals.In vitro experiments showed that the 0.5 MAC isoflurane in 60％ oxygen reduced inflammatory responses in mouse RAW264.7 cells,after LPS stimulation (all P ＜ 0.05).Suppressed activation of NF-κB pathway was also observed in mouse RAW264.7 macrophages and human PBMCs after LPS stimulation or plasma from septic patients.The 0.5 MAC isoflurane in 60％ oxygen also prevented the increases ofphospho-IKKα/β,phospho-IκBα,and phospho-p65 expressions in RAW264.7 macrophages after LPS stimulation (allP ＜ 0.05).Conclusion:Combined administration of a sedative dose of isoflurane with 60％ oxygen improves survival of septic animals through reducing inflammatory responses.