| BackgroundDuring the modern wars,the limbs explosive injury account for a large propotion.With the ever-change war mode and current weapons development,tanks,ships,armored vehicles and other combat cabins have become the main combat units for the PLA.Following these cabins are hit by gunfire,the wounded extricated from the closed compartments are often suffering from multiple and complex injuries combined with varying degrees of smoke inhalation injury.In addition,casualties with limbs explosive injury are also common at the scene of coal mine explosions,terrorist attacks,explosions and other hazardous chemicals accident.Currently,there are a number of related research reports on explosive injury and related combined injury,focused on the study of the tympanic membrane,lung and gastrointestinal and other hollow organs,as well as pathological characteristics of isolated limb explosive injury,or isolated inhalation injury.The studies on the combined inhalation injury were focused on the pathological chages of the tissue in trachea and lung,and the physiological changes of the respiratory and circulatory systems.To our knowledge,there is no research report about the pathological outcomes of the injured muscle tissue following limb explosive injury combined with smoke inhalation.Meanwhile,it lacks of necessary theoretical support for the time of surgery and the range of debridement.ObjectivesThrough the establishment of a stable experimental model of limb explosive injury combined with smoke inhalation injury to study the characteristics of pathologies and the treatment tactics,highlight the features of energy metabolism and the timeline of the pathological changes of the injured extremities after smoke inhalation,so as to provide a theoretical basis for effective treatment measures.Content and method1.The animal model: The New Zealand white rabbits were exploited.The papery point explosive source(containing 80 mg RDX)attached directly to the skeletal muscle of the limb were detonated,causing an limb injury,while using self-designed smoke generating and inhalation device,continuously and steadily providing a certain mount of smoke for the experimental animals to breathe,causing severe smoke inhalation injury,so as to develop a injury model combined the limb explosive injury with the smoke inhalation injury.2.Utilizing the random number table,the healthy New Zealand white rabbits randomized into following groups: the limb explosive injury with smoke inhalation injury group(combined injury group,CI group),isolated limb explosive injury group(explosive injury group,EI group),isolated smoke inhalation group(smoke injury group,SI group),and the control group.Following investigations were conducted to comparing those experimental groups:(1)Micro and macro pathological features in injured lung and muscle tissue of the wounds.(2)The biochemical parameters(ATP? T-ATPase? SOD? MDA? TNF-?? IL-6)associated with the muscle energy metabolism were determined from the muscular samples by microsurgical pathology and semi-quantitative analysis,to study the characteristics of each damage zones of the wound in the injured limb.(3)Physiological and biochemical changes: Vital signs(respiration,heart rate,blood pressure),arterial carbon dioxide partial pressure(PCO2),arterial oxygen partial pressure(PO2),arterial oxygen saturation(SO2),the content of carboxyhemoglobin(COHb%),tumor necrosis factor-?(TNF-?),serum leukocyte interleukin-6(IL-6),electrocardiogram(ECG)and wound microcirculation blood flow were determined.(4)Comparing the amount of muscle from surgical excision: The samples were taken 6h after injury by the trauma surgeons while he performed the wound debridement.Result1.An experiment model for limb explosive injury is developed,which is easy to operate,save and having stable injury effects.(1)A smoke generating and inhalation device is designed and produced,which can continuously and steadily release smoke.The temperature of the smoke is controlled under 40?,to avoid the side effect of heat injury.The generated smoke contains lower oxygen volume fraction,and higher carbon monoxide and carbon dioxide volume fraction,with nearly 100 kinds of organic gasses,which cause severe inhalation injury after the animal was exposured to the smoke in the device for 10 min.(2)Point source explosion created an open wound at the lateral thigh of the left hind leg of the rabbit,with an irregular shape,a few hemorrhage,muscle tissue tears,partially black dye by explosive,bruising skin around the edge of wound,scattered congestion point.No rabbit died.The difference between wounds size in both combined injury group and explosive injury group was not statistically significant(P> 0.05).2.Characteristics of injury following the limb explosive injury combined with the smoke inhalation.(1)Changes in vital signs: After the explosion,the temporary respiratory arrest or branypnea was immediately presented among the animals in explosive injury group,and returned to normal soon;and the respiratory rate and amplitude increased for 3h among the animals in combined injury group,and then breath become slow and shallow,with difficulty in breathing,wherein 17% of the animals occurred suffocations which were resuscitated after the CPR.The heart rate and mean arterial pressure significantly decreased in combined injury group immediately after injury,although these indexes increased after 30 min,but still remaining significantly lower than pre-injury value(P <0.05),and later showed the signs of shock;heart rate and mean arterial pressure slightly decreased in explosive group comparing with combined injury group(P <0.01);and during the post-injury period these two values were higher than that in combined injury group(P <0.05);changes in vital signs in that of smoke inhalation group were similar to the combined group,but the respiratory rate,heart rate,blood pressure were more stable(P <0.05).(2)ECG changes: Bradycardia were common in explosive injury group,and occasionally T waves were shown in ECG 12 h post-injury;Atria Fibrillation(16.67%)and T wave inversion(22.23%)could be found among animals in smoke injury group;atrial fibrillation(38.89%),pathological Q waves(27.78%),T-wave inversion(44.45%),ST segment depression(33.33%)were presented among the animal combined injury group after injury,although the differences of incidences were statistically significant(P <0.05)when compared with that of other two groups,but the incidences of bradycardia 12 h post-injury were not statistically significant(P> 0.05).(3)Arterial Blood Gas: Immediately after the injury,the level of COHb% were 70.3 ± 5.4% and 68.72 ± 6.4 % respectively in combined injury group and smoke injury group,indicating severe carbon monoxide poisoning,and the level of Hb CO% was still higher than that of in explosive injury group(P <0.01)and pre-injury value(P <0.05)by 6h post-injury;metabolic acidosis occurred in early stage,and the metabolic acidosis with respiratory acidosis was shown in late stage post-injury in combined injury group;the levels of arterial blood gases were normal in early stage,and metabolic acidosis was shown in late stage in explosive injury group;the changes of arterial blood gas in animals of smoke injury group were similar to that of in combined injury group(P>0.05)in early stage,and the changes of those indexes were not so obvious in late stage.(4)Changes of serum inflammatory factors: The levels of serum TNF-? and IL-6 at each time point after injury were higher than that of pre-injury in three experimental groups(P <0.05),and the most significant increase was found in combined injury group than those of in explosive injury group and smoke injury group(P <0.05).(5)Pathological features of lung injury:Under light microscope,the pathological sections of the combined injury group showed wider alveolar septum,vascular dilatation and congestion,interstitial edema and inflammatory cell infiltration at 3h post-injury;alveolar structural disorder,large number of neutrophils,lymphocytes and red blood cell aggregated in alveolar septa and alveolar,and partial lung collapsed were presented at 6h post-injury;alveolar septum rupture,severe structural damage,severe hemorrhage in alveolar septa and alveolar with a large number of macrophages,slurries and cellulose etc,and focal shrinking lung presented by 12 h post-injury.In that of smoke injury group,pathological changes were similar to that of combined injury group at 3h post-injury;the degree of aggravation in was lower than the combined injury group by 6h,12 h post-injury.In that of explosive injury group,the pathological sections showed that the structure of alveolar septa was clear and intact without leakage at 3h post-injury;alveolar septum widened at 6h post-injury,and little alveolar interstitial inflammatory exudates could be seen by 12 h post-injury.(6)Pathological features of the wounds: By microscopic pathology semi-quantitative analysis for the wounds in both combined injury and explosive injury groups,muscle tissue damage was severe within the zone ?(0-1cm),necrotic area enlarged significantly over time(P <0.05),and the difference of necrotic area between two groups was statistically significant(P <0.05)at 3h post-injury,then necrosis occurred in wide range of area in both group at 6h and 12 h post-injury,and the difference was not statistically significant(P> 0.05).The necrotic areas in zone?(1-2cm)of the wound in combined injury and explosive injury groups were significantly different at 3h,6h and 12 h post-injury(P <0.05).The necrotic areas were not significantly different between two groups in zone ?(2-3cm)at 3h post-injury,but by the 6h and 12 h post-injury,the difference was statistically significant(P <0.05).(7)Biochemical Indexes from wound muscle tissue: In combined injury group,the levels of ATP,T-ATPase and SOD in muscle tissue from the wound were lower than that of pre-injury(P <0.05 or P <0.01),and progressively decreased with time prolonged,the degrees of reduction is inversely proportional to the distance from the center of explosion;the content of MDA were negatively correlated to the changes of ATP(r =-0.973,P <0.01).In smoke injury group,the levels of T-ATPase and SOD reduced at 3h when comparing with that of pre-injury(P <0.05).In explosive injury group,the ATP content decreased as the trend could be seen in combine injury group,but the decline is less.The levels of ATP,T-ATPase and SOD in combined injury and explosive groups were at lower level at 3h without significant difference.The levels of ATP,T-ATPase and SOD in wound muscle tissue within the zone ?,? in combined injury group were lower than that in explosive injury group at 3,6h post-injury(P <0.05),more significant difference(P <0.01)was found by 12 h post-injury,but the MDA content exhibited an opposite trend.(8)Microcirculation changes in wound tissue: Microcirculation in soft tissue of wound in animals of the combined injury and explosive injury groups was harmed after the injury,caused reducing blood flow in microcirculation.The closer to the point of explosion source,the more severe damage presented.The microcirculation within zone I in both groups were severely impaired,the blood flow reduced significantly,and little perfusion remained in late stage(P>0.05);some of the micro circulation in zone ?and ? retained intact or suffering minor impairment with compensatory capacity,therefore the blood flow in local microcirculation reduced at 3 and 6 hours,and recovered by 12 h in explosive injury group,but in combined injury group,the perfusion reduced porously with time progress comparing to that in explosive injury group(P<0.01 ? P<0.05).(9)Amount of excised muscle tissue: The weights of injured muscle excised during the surgical debridement were 12.45±1.77 g and 15.72±1.70 g respectively in combined injury group and explosive injury group at 6h post-injury,and the difference was statistically significant(P <0.05).Conclusion1.The novel experimental model is simple,safe and reliable.Wherein the device we developed for the combined explosion and smoke generation experiment produce a stable flue gas,and the amount of smoke inhalation in experimental animal is not only controllable,but also has a good consistency with the severity of inhalation injury,therefore can be used as an ideal model for the relevant experiments.2.Following the limb explosive injury combined with the smoke inhalation,the cardiac function reduced,lung tissue pathological injuries were obvious,resulting in ventilator dysfunction,blood-gas imbalance,hypoxemia and metabolic acidosis with respiratory acidosis,thereby affecting the viability of the injured muscle.3.Following the combined injury,due to the toxic effects of the smoke constituents and increased ischemic hypoxia in injured muscle,enhancing the body's inflammatory response,the membrane enzyme activity decreased while the lipid peroxidation aggravated at the injured muscle,increasing the muscle energy metabolic disorders,decreasing the viability of the injured muscle tissue,consequently,the necrosis of the muscle was progressively aggravated.4.The treatment strategy for limb explosive injury combined with smoke inhalation injury should be emphasized that early correcting hypoxia,early and thorough debridement and applying effective antibiotics. |
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