| Background and objectiveFat embolism syndrome (FES) is a serious complication of fracture, usually occurs after severe trauma. Its mechanism is so complex that the pathological process has not yet been fully understood. The measures of preventing FES include early immobilization, operative fixation, drugs. It was reported that FES could be prevented by glucocorticoid and low-molecular-dextran.The clinical data showed that the preventive effect of dexamethasone combined with low-molecular-dextran on FES was better than that of low-molecular-dextran, dexamethasone alone, but even now the result is no confirmed by any animal experiment. In this study, the model of FES was established by injecting oleic acid in rats. To provide a theoretical basis for clinical application, it was observed on the model that FES was prevented by low-molecular-dextran, glucocorticoid, and glucocorticoid combined with low-molecular-dextran.MethodsPart 1:80 healthy male Wistar rats weighing 300g-320g, were randomly divided into four groups:low-molecular-dextran group (group A), methylprednisolone group (group B); methylprednisolone combined with low-molecular-dextran group (group C); control group (group D). There were 20 rats in each group.Rats were anesthetized by intraperitoneal injection with the concentration of 10% chloral hydrate solution (0.3ml/100g). After satisfactory anesthesia, the rats were fixed in prone position, and appropriate drugs were injected by indwelling catheter fixed in the tail vein.The blood samples and lung were taken at four time points(lh,2h,3h,4h) and there were five rats in each points.The lung pathological changes, PaO2, white blood cell count, tumor necrosis factor-a(TNF-a), myeloperoxidase (MPO) were detected.The results were analysised by SPSS 13.0 statistical software.Part 2:80 healthy male Wistar rats weighing 300g-320g, were randomly divided into four groups:low-molecular-dextran group (group A), dexamethasone group (group B); dexamethasone combined with low-molecular-dextran group (group C); control group (group D). each group had 5 rats. Rats were anesthetized by intraperitoneal injection with the concentration of 10% chloral hydrate solution (0.3ml/100g).After satisfactory anesthesia, the rats were fixed in prone position, and appropriate drugs were injected by indwelling catheter fixed in the tail vein.The blood samples and lung were taken at 4th.The lung pathological changes, PaO2, white blood cell count, tumor necrosis factor-a(TNF-a), myeloperoxidase (MPO) were detected.The results were analysised by SPSS 13.0 statistical software.ResultsPart 11. PaO2:The PaO2 in each group increased progressively after the injection of oleic acid.The PaO2 of Group D was low-lying and increased slowly. PaO2 at 1h,2h, 3h,4h showed:group C>group B>group A>group D.The differences between the four groups were significant (F=41.076, P=0.000);There were significant differences between the four levels of time(F=34.939, P=0.000).2. The counts of white blood cell:The counts of white blood cell in each group increased progressively after the injection of oleic acid.The counts of white blood cell of Group D was low-lying and increased slowly. The counts of white blood cell at 1h showed:group B>group A>group C>group D,at 2h,3h,4h,showed:group C>group B>group A>group D.The differences between the four groups were significant (F=4.258, P=0.022);There were significant differences between the four levels of time(F=25.062, P=0.000) (P<0.05).3. TNF-a:The TNF-a in each group increased first,and then decreased.The TNF-a in all groups peak at 2h,the TNF-a in each group at 4th was lower than the initial value separately. There were stasticial differents between the initial values of TNF-a in all the groups,The TNF-a in Group D was most in all the groups.The results of TNF-a showed that:There were significant statistical differences between the four groups at 1h,2h,3h,4h (F=50.074, P=0.000; F=46.338, P=0.000; F= 67.575, P= 0.000; F= 73.879, P= 0.000). There were significant statistical differences between the four groups at 1h,3h. There were significant statistical differences between the four groups at 2h (P<0.05),except group A,D (P=0.679>0.05) and B,C (P=0.196>0.05). There were significant statistical differences between the four groups at 4h (P<0.05,statistically significant difference),except group A,B (P=0.070>0.05) and B,C (P=0.063>0.05)4. MPO:The MPO in each group increased first,and then decreased.The initial values show that:Group D>Group A>Group B>Group C.The MPO in each group all reach its peak after 3h.At 4h,the MPO in Group D,Group A was separately higher than the corresponding initial value and the MPO in Group B,Group C was separately lower than the corresponding initial value. The results of MPO showed that:There were significant statistical differences between the four groups at 1h,2h, 3h,4h (F=13.257,P=0.000; F=23.716,P=0.000; F=6.204,P=0.005; F=73.285,P=0.000). There were significant statistical differences between the four groups at 1h (P<0.05,statistically significant difference),except group A,D (P=0.216>0.05) and B,C (P=0.147>0.05). There were significant statistical differences between the four groups at 2h (P<0.05,statistically significant difference),except group B,C (P=0.104>0.05). There were significant statistical differences between the four groups at 3h (P<0.05,statistically significant difference),except group D,A (P=0.283>0.05);A,B (P=0.245>0.05) and B,C (P=0.091>0.05). There were significant statistical differences between the four groups at 4h.5. HE staining:The lung slices was stained with HE after 4 hours.The results showed that:group A, group B present alveolar interstitial edema, alveolar effusion more slightly than group D;Group C presents the most slightly alveolar interstitial edema, alveolar effusion in all of groups; Group D show the most serious alveolar interstitial edema, alveolar effusion.6. Methyelin staining:After 4 hours the lung tissue was was stained with methyelin, the result showed that:group A, group B present alveolar interstitial edema, alveolar effusion more slightly than group D;Group C presents the most slightly alveolar interstitial edema, alveolar effusion in all of groups; Group D show the most serious alveolar interstitial edema, alveolar effusion.7. The ultrastructure of electron microscope:After 4 hours the lung tissues was counterstained with uran-lead, the result showed that:group A, group B present oleic acid drops, WBC, cellulose, the swelling of mitochondrias inâ…¡-type cell; Group C:the lamellar bodies inâ…¡-type cells were intact, mononuclear cells and red blood cell in alveolar cavity; D Group:alveolar space, there macrophages and cellulose,the degeneration ofâ…¡-type cells, the broken lamellar body in cytoplasmic. Part 21. PaO2:GroupC>GroupB>GroupA>GroupD at 4h.The results of PaO2 showed that:statistical differences between the groups(F=19.717, P=0.000). There were significant statistical differences between the four groups(P<0.05,statistically significant difference),except group A,D (P=0.456>0.05)2. The counts of white blood cell:GroupD>GroupA>GroupB>GroupC at 4h.the results of the counts showed that:no statistical difference between the groups (F= 2.051, P= 0.147).3. TNF-a:GroupD>GroupA>GroupB>GroupC at 4h.The results of TNF-a showed that:statistical differences between the groups (F=5.341, P=0.024). There were no difference between the groups by the method Dunnett's T3.4. MPO:GroupD>GroupB>GroupA>GroupC at 4h.The results of MPO showed that:statistical differences between the groups(F= 5.743, P= 0.007). There are statistical differences between the four groups(P<0.05,statistically significant difference),except group A,B (P=0.305>0.05),and A,C (P=0.275>0.05)5. HE staining:The lung slices was stained with HE after 4 hours.The results showed that:group A, group B present alveolar interstitial edema, alveolar effusion more slightly than group D;Group C presents the most slightly alveolar interstitial edema, alveolar effusion in all of groups; Group D show the most serious alveolar interstitial edema, alveolar effusion.6. The ultrastructure of electron microscope:After 4 hours the lung tissues was counterstained with uran-lead, the result showed that:group A, group B present oleic acid drops, WBC, cellulose, the swelling of mitochondrias inâ…¡-type cell; Group C:the lamellar bodies inâ…¡-type cells were intact, mononuclear cells and red blood cell in alveolar cavity; D Group:alveolar space, there macrophages and cellulose,the degeneration ofâ…¡-type cells, the broken lamellar body in cytoplasmic. ConclusionFES can be prevented by glucocorticoid combined with low-molecular-dextran. The effect of methylprednisolone combined with low-molecular-dextran was better than that of low-molecular-dextran, methylprednisolone alone in preventing FES The effect of dexamethasone combined with low-molecular-dextran was better than that of low-molecular-dextran, dexamethasone alone in preventing FES.The mechanism may be that the cell membrane of macrophage and neutrophil was stablised by glucocorticoid and low-molecular-dextran, or the aggregation of leucocytes was reduced by low-molecular-dextran,the cell membrane of macrophage and neutrophil was stablised by glucocorticoid;thereby reducing the generation of TNF-a, MPO.
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