Study Of Blast Injury Combined With Hemorrhagic Shock In Enclosed Space And Resuscitation

Armored vehicles,which has typical enclosed space, are main combat equipments and the primary target assaulted in modern battlefield. The incidence rate of terrorist attacks aiming at confined spaces full of people such as bus, subway and public works is increasing all over the world. As a result, the incidence rate of blast in enclosed environment is extremely high in both dailylife and wartime. A great number of studies have shown the characteristic and mechanism of damnification in major organs; and blast vave in closed environment is different from open environment. In enclosed space, complex blast wave characterized with including reflected shock wave, superposition, multiple stress peaks overlapping and long duration of overpressure can result in serious contusion of organ and tissue particularly in lung and brain. Pieces of bullet and cabin may hurt great vessels which leads to life threaten blood lost. Consequently, blast in enclosed environment could result in injury by complex shock wave. Thus, serious wounded combined with serious shock is under high ratio.Shock, the certain process from trauma to multiple organ failure, is charactered of effective circulating blood volume decrease, perfusion disorder, inflammatory mediator production and high oxidative stress. Volume resuscitation plays an important role in care of combat trauma. Previous research announced the characteristics of shock induced by shock tube and burn, but few were focused on the shock caused by blast in enclosed space. The aim of this study was to investigate the hemorrhagic shock folloing blast injury in enclosed space and its relationship with inflammatory cytokines(TNF,IL-6),oxidative stress and CSE/H2S system, which has been reported has protective effect on the blast lung injury .The organ damage of lung, brain, liver were observed. Then volume resuscitation with crystal, colloid, hypertonic saline were performed.This study includes three parts, the main results and conclusions are as follows:PART I Characteristics of the shock induced by blast injury combined with hemorrhage in rats.Rats were postioned in a stimulated armored vehicle cabin, and detonator (400mg diazodinitrophenol) was fixed 11cm away from the center line of rat abdomen and chest, then exploded. The smoke was quickly detached from the cab immediately following explosion. Pressure changes in the cabin was detected and recorded with a data acquisition system then analyzed through Origin7.0 system. Then the rats were bled from femoral artery catheter within 30mins of 30% of the total blood volume to simulate hemorrhagic shock following blast injury. Rats in open space group were submitted to same process except experiencing blast injury in open space. The control group rats only underwent hemorrhage. Blood pressure changes and death rate are compared within these three groups. It is shown that in our experiment blast wave in enclosed space is complex, rats in enclosed space group(ES) endured faster blood pressure (BP) decrease and eailer death compared to open space group(OS) and the control group. Changes of hemodynamics, blood gas and plasma inflammatory were tested. It is shown that compared with OS rats, ES rats endure lower PO2 and oxyhemoglobin saturation and more lactic acid accumulation.The initial time of BP decline and lactic acid accumulation rise is earlier, changes are more obvirous. Perfusion level of vital organ is lower in ES group than OS group.Brain and hepatic organ exist obvious blast injury, but organ rupture and main vessels bleeding was not observed. The water content ratio of lung and brain in ES group are higher than control. Pathological changes of lung, liver and brain tissue were observed, peroxidatic reaction level of lung and variance in CSE/H2S system was tested. It is shown that lung, liver and brain tissue contusion is observed in both of the two groups, and the injury is more severe in ES rats. Compared with OS group, MAD and MPO were more activated in ES group, combined with higher H2O2 concentration and lower SOD activity of lung tissue (p<0.05). Meanwhile, the CSE activity and H2S concentration of lung tissue decreased significantly (p<0.05). The index related closely with the blood perfusion of lung and brain tissue, inflammatory factor and oxidative stress injury of lung tissue, which points out that CSE / H2S system may participate in the regulation of the process of lung injury and shock induced by blast injury.Thus, a reproducible rat model of blast injury combined with hemorrhagic shock in enclosed space was successfully established. It is also manifested that shock induced by blast injury combined with hemorrhagic is different from the common traumatic shock or hemorrhagic shock.PART II Effect of different type of liquid in volume resuscitationBased on hemorrhagic shock caused by Blast injury and hemorrhage, the rats were conducted early fluid resuscitation. Rats were randomly divided in to normal saline (NS), hydroxyethyl starch (HS), and 7.5% hypertonic saline/6% dextran (HSD) groups.Mean arterial pressure changes were recorded; 8 rats were killed at 150min, 210min, 270min after blast injury, and the pathological alterations in each group was observed. The arterial blood gas, concentration of plasma inflammatory cytokines is detected at all time points to evaluate the resusciatation effect of different fluids. The lung, brain water content ratio was calculated. Take lung as representative damaged organ, the peroxidation level and CSE/H2S concentration is tested to evaluate the organ protective effect of different resuscitation fluid Organ blood flow changes were detected with SEDIMENTATION colored microspheres during shock process. Results: HSD can significantly increase blood pressure, vital organs blood flow, improve blood gases parameters, inhibit inflammation, reduce oxidative stress and lung injury (p <0.05)..PART III Role of preventive exogenous donator of H2S(NaHS) administration in hemorrhagic shock following blast injury in enclosed spaceExogenous H2S donor was induced by intraperitoneal injection before the rats were conducted blast injury, then the rats were resuscitated with HSD. Other disposal is the same to experiment I of part II. Results: Compared to other resuscitation group,increased blood flow and lower inflammatory factors level in blood and peroxidation level in lung tissue were detected, the difference was significant (p <0.05). Lung and brain water content decreased significantly (p<0.05).The above results show that:1. Shock resulted from explosion injury and blood loss charactered of early on set time, poor blood flow perfusion, fulminating anoxia and acidosis, obvious inflammation, severe pneumonedema, brain edema and tissue/organ damage differed from simple hemorrhage Shock. Compared with OS and control group, Shock in ES was more severe, with worse outcomes and high mortality. Blast injury also exist in OS group, but it was pretty better than ES group. 2. 7.5% hypertonic saline/6% dextran (HSD) is more suitable for volume resuscitation therapy of the shock in duced by blast injury combined with hemorrhagic shock in rats, which can effectively improve hemodynamics, reduce inflammation, improve the oxidation stress injury, and protect the lung and brain.3. Lung CSE/H2S system might mediate the shock process following blast injury in enclosed space. Pulmonary blast injury and inflammation level was reduced by preventive administration of exogenous donator of H2S(NaHS) in low doses(10mg/kg),and rats outcome was improved.