| Background:Sepsis-associated encephalopathy (SAE) is an acquired brain injury syndrome and defined as a diffuse or multifocal cerebral dysfunction induced by the systemic response to the infection without clinical or laboratory evidence of direct brain infection.SAE is, caused by sepsis, common complication of central nervous system. presentation of SAE is highly variable. In early stages, patients display impaired attention, concentration, confusion, and disorientation. Progression is characterized by paratonic rigidity and increasing depression in consciousness; in its last stage patients are comatose. The incidence of SAE was9%-71%in ICU. Altered mental status is present in up to23%of patients with sepsis and can even precede the cardinal findings of sepsis particularly in older or immunosuppressed individuals. In a recent epidemiological multicentric study with497patients, including76septic patients, the overall prevalence of delirium was32.3%.It is associated with a substantial increase in mortality of up to49%, compared with26%in those without neurologic symtoms. SE not only is associated with high hospital mortality (16%-63%), but also can lead to long-term cognitive and functional limitations in those patients who survive. Therefore, It is particularly important to correctly identify the presence and to give timely intervention for patients with severe brain injury. The pathophysiology of SAE appears to be multifactorial. The disease results from the interaction and overlapping of various mechanisms related to the systemic inflammatory response, including oxidative stress,proinflammatory and anti-inflammatory mediators, the complement cascade, endothelial dysfunction, bloodbrain barrier disruption, and microvascular failure. This entire process leads to dysfunction, apoptosis, and cell death. Therefore, the development of this disease is more closely related to the inflammatory response than to the infectious agent alone. Because the pathogenesis is not clear, so far there is no exact diagnostic criteria, nonspecific clinical manifestations such as consciousness change, disorientation, inattention, delirium, coma are existed in common diseases, and will change with the different depth of sedation. So it is need for SAE diagnosis to exclude other metabolic and structural abnormalities encephalopathy. Currently, the diagnosis of SAE mainly depends on the electrophysiological, biochemical tests and imaging, but there are some limitations, none of the EEG findings are pathognomonic, and its usefulness in aiding SAE diagnosis also lies in exclusion of nonconvulsive status epilepticus. And EEG can not be applied to patients in sedation or metabolic disorders. Somatosensitive Evoked Potentials(SEPs),due to complicated operation,can not often be implemented, and it seems the severity of the clinical manifestations are not positively correlated with SEPs. Usually Cerebrospinal fluid(CSF) analysis of SAE patients are normal, part of those are higher protein concentration, but fickle. Neuron-specific enolase (NSE) and S100beta serum proteins have been proposed as a biomarker for the diagnosis of SAE, but there are a number of studies suggest that there are inconsistant concentration of NSE in serum and cerebrospinal fluid with SAE diagnosis, and no evidence to show that acute inflammation can cause elevated specific brain proteins concentrations in the serum. Some studies found no correlation between the increased S100beta serum concentrations and the development of SAE, Its concentration increases from the outside of the brain tissue (S100beta protein concentration in adipocytes and chondrocytes is up to1/4in brain). Head computed tomography (CT) of SAE patient usually failed to find abnormal signal. Magnetic resonance imaging(MRI) can be used to rule out structural abnormalities of brain diseases,and the part of the SAE patient can also be found abnormal signal, but unstable. The Magnetic resonance spectrum (MRS)is a kind of noninvasive detection technology for quantitative analysis of metabolic compounds on living tissue. The common tested metabolic compounds include:1. N-acetyl aspartate (NAA):is an integrity markers of the neuron about mitochondrial metabolism function. The decrease of NAA reflects The loss and dysfunction of neurons, and associated with cognitive dysfunction and The degree of brain injury.2.Choline (Cho):is a synthetic precursor of the neurotransmitter acetylcholine and phosphatidyl choline which is main ingredients of cell membrane, the higher peak shows that the cell membrane synthesis or cell quantity were increased, this is related to the recovery of neuron injury.3.Creatine (Cr): plays a role of relying on the system in maintaining the energy of brain through reserving of the high-energy phosphate bonds and buffering between adenosine triphosphate (ATP) and adenosine diphosphate. Due to the concentration of total creatine is relatively stable in the human body; the signal strength is easy to lead to artificial signal change of NAA and Cho due to non-uniform magnetic field and radio frequency while MRS examination, so Cr often is applied as an internal reference standard to correct. MRS technology has been used currently in the diagnosis and assessment of traumatic brain injury, hypoxic ischemic encephalopathy, intracranial infections and other diseases.Purpose:To explore a more accurate diagnostic techniques for the early diagnosis of brain injury caused by sepsis, evaluation of treatment and prognosis, magnetic resonance spectroscopy of brain injury were studied through rat model of sepsis established by intraperitoneal injection of LPS. Methods:The35SD rats were randomly divided into four groups, normal control group (n=5),6h group (n=10),12h group (n=10),24h group (n=10). Referring Remick DG et al sepsis modeling,SD rats had a30mg/kg dose of LPS intraperitoneal injection in experimental groups for sepsis model; while the control group received normal saline. Experimental groups were anesthetized by intraperitoneal injection with3%sodium pentobarbital solution (0.2mL/100g) after the corresponding time points of model6h,12h,24h;24h subjected to the same anesthesia for control group. Rat heads were fixed in a special Plexiglas stereotactic frame after successfully anesthetized, and detected by magnetic resonance imaging and spectroscopy(right hippocampus), All imaging conditions referenced Bozza FA et al study on a7T,30cm horizontal bore magnet (BRUKER Company, Model:Biospec70/20USR, Germany), using a G060gradient set and a whole-body multi-rung38mm resonator.After finished the examinations, chest of anesthetized rats immediately were opened to expose heart. After blood samples were collected with a syringe inserted into the left ventricle through the apex(4℃,3000rpm for10minutes,separate the serum to0.5ml EP tube and preserve in-70℃for the protein concentration of NSE and S100beta detection), a small hole was Cut in the right atrial appendage for bloodletting, after that rapid perfusion with150mL0.9%sodium chloride solution, and then slow down the speed until the right atrial appendage perfusion outflow clear liquid, then continue perfusing with150mL4%paraformaldehyde dissolved in0.1mol/L phosphate buffer (PBS) for1h. Then open the rats skull,and take the brain tissue to fix in4%paraformaldehyde for standby(Take right side of brain tissue, dehydration, paraffin embedding, slice8μm thickness for HE, Nissl and TUNEL staining, and then observe the pathological changes of the hippocampus by microscope).Results:35SD male rats results in the corresponding time points died two survived eight(6h group); died one survived nine(12h group); died two survived eight(24h group). And the surviving rats were mental malaise, piloerection, drowsiness, eyes and noses bleeding, diarrhea and other manifestations of sepsis,even12h and24h group is particularly evident, while the control group no such performance. There were no significant difference about T2-weighted imaging in6h,12h,24h group of sepsis compared with control group; high signal didn’t appear near large blood vessels at the base of the brain. Spectra were collected by1H-MRS technology on the right hippocampus. There existed some different peaks between different groups of NAA, Cho and Cr, NAA/Cr ratios were compared by variance analysis between different groups, there were statistically significant (P=0.000). Pairwise comparisons showed that, in addition to comparing between12h and24h group,there are statistical differences between other groups;While Cho/Cr ratio was compared among the different groups by the Kruskal-Wallis test, there were statistically difference (P=0.023), which be considered Cho/Cr ratios difference among the different groups, Pairwise comparisons showed that, in addition to comparing between the control and24h group,there were no statistical difference between the other groups. NSE serum concentration was compared among the different groups by the Kruskal-Wallis test, there were statistically difference (P=0.000), which be considered NSE serum concentration difference among the different groups, Pairwise comparisons showed that, in addition to comparing between the control and12h group,there were no statistical difference between the other groups; The serum concentration of S100beta protein was compared among the different groups not only method but also results as the same with NSE, but Pairwise comparisons showed that, in addition to comparing between the control and6h or12h group,there were no statistical difference between the other groups. HE staining results:It was normal tissue and cell morphology and no significant pathological changes in control group; in6h group local neurons arranged in loose, individual neuron cells were deform and karyopycnosis; neurons were reduced, loosely arranged, some neurons cell deformed and karyopycnosis,even lose sub morphology in12h group; comparing with12h group, in24h group neurons significantly were reduced, most neuronal cells were deformed and losed sub morphology as zonal distribution. Nissl staining results:Nissl bodies of neuronal cell were normal in the control group; but in the6h group individual neurons were deform and Nissl bodies were disappeared; in the12h and24h group there were more Nissl bodies disappearing and part of neurons were deform. TUNEL staining results:In the hippocampus the expression of nerve cells were negative in control group; and weakly positive for individual nerve cells in6h group; positive for more nerve cells in12h group; but in24h group expression of widespread nerve cells were positive. Cells apoptosis rates were compared by variance analysis between different groups,there were statistically significant (P=0.000). Pairwise comparisons showed that, in addition to comparing between12h and24h group,there are statistical differences between other groups. Conclusion:The magnetic resonance spectrum can be used as a more sensitive method for the early diagnosis of brain injury caused by sepsis. It also will be an accurate technique to assess the treatment effect for this disease, which help us to judge the prognosis. |
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