Effect of Polyethylene Glycol on the Resuscitation of Endotoxemia of Rats
|School||Southern Medical University,|
|Keywords||drag reduction agent polyethylene glycol Endotoxemia septic shock microcirculation fluid resuscitation|
Endotoxemia is a syndrome called systemic inflammational response syndrome, which caused by bacteria in blood or in lesions release large amounts of endotoxin into the blood or enters a large number of liquid contaminated by endotoxin. Usually, endotoxemia lead to lethal septic shock and multiple organ failure disseminated intravascular coagulation with a high mortality rate. Endotoxemia and septic shock is one of the main reasons. With the use of antibiotics, progress in intensive care and support in recent years, the mortality rate of endotoxemia and septic shock has step down, but still as high as 30-60% according to foreign literature.The development of endotoxemia can be divided into two phases:in the early phase, the cardiac output and tissue perfusion were increased significantly, accompanied by a reduction in peripheral vascular resistance. In the late phase, cardiac output decreased significantly, systemic vascular resistance increased, the number of open capillaries reduced, even microcirculatory blood flow stops. The microcirculation barrier formed in this period including of micro-vein permeability increased, leukocyte activation and adhesion, oxygen free radicals around the blood vessels increase, accompanied with the disseminated intravascular coagulation caused by the abnormal blood coagulation state of capillaries. Microcirculation disturbance and tissue edema concomitantly can led to oxygen supply of the tissues reduce and the tissue oxygen supply and demand imbalance, caused the cell injury and trigger the inflammatory signaling pathway at the same time, and further aggravate tissue damage. The endotoxin septic shock caused by refractory hypotension occurred during this period can increase the mortality significantly. During the endotoxemia, the abnormal distribution of blood flow caused tissue ischemia, decreases the organ perfusion and the oxygen carrying capacity, increased anaerobic metabolism and the lactate concentration in blood. Therefore, lactate in blood as one of an important indicator of systemic infusion and oxygen metabolism to evaluate the severity and prognosis of shock.The multiple organ failure result from severe endotoxemia and septic shock is the ultimate cause of death, the microcirculation is an important part of the development. Fluid resuscitation remains the primary treatment of maintain cardiovascular function and restore hemodynamics, tissue and organ perfusion in early endotoxemia, this treatment can restored blood volume and improve circulation of blood pressure and heart rate index, but it is not ideal in improving the survival rate. The reason may be about not to improve the microcirculation. There are studies have found that the patients in worse microcirculation with worse prognosis,and the patients of endotoxemia in faster improvement of microcirculation with a higher survival ratio.The sustained deterioration of the microcirculation lead to multiple organ failure,even the death. The mortality will be significantly improved when improving the microcirculation as soon as possible in the early 24 hours of endotoxemia. A prospective study with early microcirculatory perfusion index in endotoxemia patients in 2007 showed that that the EMCPI was significantly impaired in deaths and patients with progressive failure in cardiovascular system. Therefore, to improve microcirculation, improve tissue perfusion and prevent multiple organ failure is the main direction in treatment of endotoxemia and septic shock. Drag-reducing polymers is a kind of high molecular compound that be able to reduce the flow resistance. B.A.Toms first reported the drag reduction phenomenon(Toms effect) in 1948:the small amount of DRPs in the liquid fluid in the pipe can reduce the turbulent transport resistance, which in the case of constant delivery pressure to increase traffic, or traffic unchanged to lower delivmolecularpressure, a number of effective concentrations of DRPs in the case of only ppm can be reduced by 50% or more of the resistance. DRPs are widely used in the current pipeline (oil, natural gas), aerospace, marine diving and other fields. Applications in medicine and research after 1970s, the early work focused on the blood and fluid mechanics and other aspects of atherosclerosis. DRPs in the medical application of a synthetic polymer and natural materials made of polysaccharide polymer from plants, bacteria and animal blood. Representative synthetic materials DRPs polyethylene glycol (PEG), anionic polysaccharide (Separan), polyoxyethylene (PEO). It has been proved that the DRPs can increase coronary blood flow and improve the prognosis of acute ischemic animal, inhibit atherosclerosis in vivo plaque formation. In recent years, more studies are concerned with the DRPs used in the treatment of hemorrhagic shock, intravenous injection of DRPs to increase survival of hemorrhagic shock animals, improve the organization and tissue perfusion of oxygen supply.As the complexity blood as the object of research, specific mechanisms of DRPs to improve the hemodynamic still unclear at present. Studies pointed that only a few parts per million concentration can be significantly improved hemodynamics, its role in the shock fluid resuscitation does not seem to increase blood volume, on the contrary can reduce the shock and resuscitation fluid requirements, After a lot of fluid resuscitation to avoid extensive tissue and organ edema. At the same time, DRPs reduce blood viscosity, so that blood flow, lubrication easy flow of blood vessels and contribute to capacity through the capacity before the blood vessels. Experiments show, DRPs can increase blood flow velocity in the microcirculation by reducing the blood cell aggregation and deformability change of red blood cells. In normal circumstances,under normal circumstances, the distribution of red blood cells in microvascular blood flow in the blood flow in the main axis, near the edge of the blood vessel wall often no red blood cells, this phenomenon called blood whitewash effect. And this blood whitewash effect is more severe under shock. DRPs may improve the Blood whitewish effect, so that cell-free plasma layer near the wall thickness decreased, red blood cells and thus more conducive to red blood cells near the wall to carry the gas exchange of oxygen and organizations to improve the oxygen supply, thus improving microcirculation perfusion.It has not been reported that DRPs for endotoxemia and septic shock. In this study,we establish the animal models of endotoxemia by LPS, based on application of polyethylene glycol treatment of endotoxemia, observe the survival time, blood flow dynamics and hemorheology, lactate concentration and changes in microcirculation images in animal model of endo toxemia,to explore the the rapeutic effect of DRPs to endotoxemia and septic shock,and provide effective theoretical and experimental basis for endotoxemia and septic shock therapy in the future.Materials and methods:1. Preparation of DRPs: Accurately weighed PEGlmg, add saline 100ml, prepared into a concentration of 1×10-5g/ml solution, and then prepared PEG solution into the molecular interception was 40000Da dialysis bags, dialysis in saline 24h, removal no drag reduction effect of impurities and small molecule PEG. Stored in 4℃refrigerator for use.2. Experimental animal preparations and groups: 20 Wistar rats of either sex, weighing 180～220g. Drinking water and with free feed before the experiment day.Randomly divided into saline control group (Control group) and polyethylene glycol group (Observation group), n=10.3. Animal model:Intraperitoneal injection of pentobarbital sodium (40mg/kg) anesthesia, the line of the right femoral artery, connecting arterial pressure measurement devices, continuous monitoring of mean arterial blood pressure; the right femoral vein cannulation to establish intravenous access. Isolated ridge oblique, placed under the microscope microcirculatory blood flow, the interval for video capture local micro-circulation images.Femoral vein endotoxin (LPS) 10mg/kg, mean arterial blood pressure changes observed.4. Packet recovery:Model after successful resuscitation. Observation is polyethylene glycol group, enter the compound sodium chloride+ PEG solution (containing polyethylene glycol 50μg/kg) Control group, NS group, enter the compound sodium chloride+saline (solution with polyethylene glycol equivalent) for fluid resuscitation the speed of the two groups are 25ml/kg/h continuous infusion from the femoral vein 2 hours.5. Data collection: Oblique ridge of the good separation observed under the microscope microcirculation, and records began modeling, model success and the end of the recovery vessel diameter, white blood cell count, the number of rolling speed and adherent. Blood specimens were taken while the blood lactate concentration, mean arterial blood pressure recorded. Recorded in rats after fluid resuscitation survival. 7.Data analysis:All data were analyzed SPSS13.0 package measurement data, results are expressed as mean±standard deviation, the trend between two sets of data using repeated measures analysis of variance, the two groups after administration of the data were completely random design data variance Statistical analysis. P<0.05 as statistically significant difference.Results:1. After endotoxin microcirculation of rats could see the blood flow slowed down, increasing the number of white blood cells, slow rolling, adherence increased, even a partial phenomenon may appear white blood stasis, blocking part of the capillaries.Compared with the control group, continued to pump into the femoral vein to give polyethylene glycol solution, the rat dorsal oblique muscle microvascular blood flow was significantly faster, reduce the number of blood leukocytes, rolling speed, reduce some block microvascular recanalization.2. a successful model of endotoxemia in rats, the rats based on blood pressure, mean arterial pressure dropped to 2/3, given the recovery of PEG was significantly higher blood pressure, the difference was statistically significant. 3.endotoxemia in rats significantly increased blood lactate concentration, the recovery of rats given PEG artery lactate concentration was significantly lower than the control group, a statistically significant difference.4. given the recovery of PEG was significantly higher survival time in rats.Conclusion:1. The polyethylene glycol to improve the early endotoxemic rats during fluid resuscitation of the microcirculation, so that the rat dorsal oblique muscle microvascular blood flow was significantly faster, reduce the number of blood leukocytes, rolling speed, reduce some of microvascular occlusion recanalization. 2.The same amount of fluid resuscitation in the given case, the application of PEG recovery in endotoxemic rats blood pressure is more stable.3.The recovery of polyethylene glycol in rats given blood lactate decreased more significantly, indicating that PEG will be more conducive to improving systemic perfusion in endotoxemia and oxygen metabolism in rats.4. Polyethylene glycol to can prolong the survival time of rats in endotoxemia, but can not change the prognosis.