Materials and Methods: A total of 18 adult sheeps, weighing 35-45kg, were used. The animals were treated in accordance with National Health and Research Council Ethics Committee Guidelines. Full approval was obtained from the Kitasato University Animal Ethics Committee. This experiment involved three groups (each, n=6) of sheep: reamed femoral nailing (RFN) groups, unreamed femoral nailing (UFN) group, and sham operation control (SOC) group. Femoral osteotomies, shock status, and post-traumatic wet lung conditions were not made throughout this experiment, in order to evaluate pure deleterious effects on pulmonary and systemic function induced by reamed or unreamed femoral nailing. The animals were ventilated using volume-controlled ventilation under halothane anesthesia with an FIO2 of 50% and a tidal volume of 15ml/kg with 5cmH2O of positive end-expiratory pressure. Hemodynamic monitoring data including cardiac output (CO) and blood gas data were recorded, and also biochemical samplings (AT III, LPO, triglyceride, fibrinogen) via central vein were collected during reaming or insertion of the nails and 0 to 6 hours after nailing. Systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), and A-aDO2 were calculated at each period on the basis of the above hemodynamic and blood gas data. Bronchoalveolar lavage fluid (BALF) in each animal was analyzed at 6 hours after nailing. The percentage of lavage cells containing neutrophil or brown-red fat droplets (lipid-laden cells) were calculated after examination of at least 200 cells on the slides stained with Sudan III.. Myeloperoxidase (MPO) activity (U/g protein) in the pulmonary tissue was also examined after BAL. Both the BALF analysis and the MPO analysis were performed by the same technician without prior knowledge of RFN, UFN, and SOC group. All values are expressed as mean±SEM. All time-dependent parameters between three groups were analyzed using two-way repeated-measures ANOVA with post-hoc test. The cell counts in BALF and MPO activity data between the groups were analyzed using one-way ANOVA with post-hoc test. Statistical significance was defined as p<0.05.