The Pathologic And Pathophysiologic Characters Of Acute Lung Injury Induced By Seawater Drowning And The Effects Of Ventilation Treatment

Acute lung injury (ALI) is a common clinical emergency. Studies at home and abroad demonstrated that the main pathological features of ALI are edematous alveoli and lung parenchyma, broken alveolar septa, fusion of alveoli, collapse of many alveoli, and alveoli irregular in size. Its main pathophysiological features are hypoxemia and instability of hemodynamics. Drowning is the second lethal factor on the sea at peace and war. Compared with other factors leading to lung injury , seawater may directly damage alveolar epithelial cells and endothelial cells, and initiate the lung inflammation which may lead to other injuries.Seawater drowning induced acute lung injury (SWD-ALI), is quite different from other common ALI, and is characterized by severe trauma, rapid progress, complicated changes and difficult treatment. Up to now, there is no study which clearly clarified the pathological and pathophysiological features of SWD-ALI, and whether they are different from those of ALI. All these may influence the definition and diagnosis of SWD-ALI. In this study, the animal model of SWD-ALI and its standardization were researched for the first time. The pathology and pathophysiology of SWD-ALI were profoundly studied, and the relationship between pathological changes and radiological appearance of lungs were evaluated, in order to understand and standardize the diagnosis of SWD-ALI.In this study, seawater was poured into New Zealand rabbits by the airway catheter and the animal model of SWD-ALI was established based on the realistic situation and complying with the diagnostic standard at home and abroad. HRCT findings showed that there was asymmetry ground-glass opacity in the lungs of the animals suffered from SWD-ALI, with consolidation in the downward sites, whereas the area of all lesions was less than 1/2 of the total area of a lung. The histological study showed that in the experimental group, the downward sites of lungs appeared congested and edematous, which was called "hepatization". On cut surface, the lesions became dark red with the effusion of reddish edematous fluid. Microscopically, the alveolar septa became markedly damaged and the fusion of alveoli appeared. Alveoli and lung parenchyma were edematous. The inflammatory cells infiltrated into the lung parenchyma and alveolar cavities. The broken alveolar septa and inflammatory cells infiltration are the main pathological features, which is different from the other ALIs whose histological feature is appeared. Alveoli and lung parenchyma were edematous. The inflammatory cells infiltrated into the lung parenchyma and alveolar cavities. The broken alveolar septa and inflammatory cells infiltration are the main pathological features, which is different from the other ALIs whose histological feature is the edematous alveoli and lung parenchyma. It may be due to the direct damage of the seawater. Electronmicroscopically, the cells appeared severe degeneration, with various degrees of damage of basal membrane. Type I and II pneumocytes swelled, and many type II pneumocytes shed into the alveolar cavities. The cytomembranes of endothelial cells were damaged, the cytoplasm swelled and the basal membranes of vessels exposed. Many mitochondria swelled and became vacuolated, and mitochondrial cristae were broken. The number of multilamellar bodies reduced.In SWD-ALI, the hemodynamics also became unstable. After seawater being poured, the animals in the experimental group immediately demonstrated the reduction of heart rate and mean systemic blood pressure. The reason may be because of the contraction of lung vessels induced by hypoxemia.The former studies showed that mechanical ventilation was the principal treatment of SWD-ALI. However, in the cases of SWD-ALI, the damage of alveolar epithelial cells induces to reduction or even loss of secretion of pulmonary surfactant, leading to the collapse of many alveoli which are difficult to recover, and resulting in the shunt in lungs. In mechanical ventilation, the shear stress between the overdistended alveoli and collapsed alveoli may worsen the lesions of SWD-ALI. When treating SWD-ALI, conventional mechanical ventilation (CMV) often leads to ventilation associated injury (VAI), resulting in the high mortality of SWD-ALI. Although protective lung ventilation strategy may help to avoid the barotraumas, it is unfavorable to the recovering of collapsed alveoli. In order to enhance the survival rate, a new treatment to recover the collapsed alveoli should be developed. Sustained inflation (SI), a new recruitment method, provides adequate pressure to the airway by mechanical ventilation, keeping the collapsed alveoli open. After sustaining some time, the stability of the alveoli increases, and the shear stress between the overdistended alveoli and collapsed alveoli can be reduced. But it is uncertain whether SI could be applicable to the treatment SWD-ALI, which is more severe than ALI.In this study, protective lung ventilation strategy was, for the first time, combined with SI in the treatment of SWD-ALI, in order to evaluate the safety and effectiveness of SI treatment.This study demonstrated that, by providing more pressure to the airway, SI made more collapsed alveoli recover and facilitated the distribution of air in lungs; thus the shunt reduced and ventilation/perfusion ratio increased, improving blood oxygenation in lungs. Lasting some time, SI facilitated the uniform distribution of air in the alveoli with different time constants and extended the time of air exchange; and therefore improved the blood oxygenation. Combined with small tidal volume, sustained inflation could amend the shortcomings of protective ventilation strategy, improving the oxygenation in the cases of SWD-ALI and facilitating the recovering of the collapsed alveoli; and thus led to the improvement of lung compliance. In the treatment of SWD-ALI, combined with protective lung ventilation strategy, SI could markedly enhance the oxygenation level, recover the collapsed alveoli to some extent, improve lung compliance and reduce the lung injury. Therefore, SI is a safe and effective mechanical ventilation method to treat SWD-ALI.By establishing and standardizing the animal model of SWD-ALI, this study clarified the main pathological and pathophysiological features of SWD-ALI. Different ventilation methods, especially the safety and effectiveness of SI in the treatment of SWD-ALI, were studied, in order to improve the salvation system of seawater drowning and provide the technical preparation for the sea battles.