Inhalation injury

　　The main cause of aspiration injury is thermal action, but at the same time, the inhalation of a large amount of unburned smoke, carbon particles, and irritating chemical substances also causes damage to the respiratory tract and alveoli. Therefore, aspiration injury is a mixed injury of heat and chemicals.

　　Aspiration injury is related to the environment of injury. It often occurs in poorly ventilated or enclosed spaces, especially during explosions and fires. In this environment, the concentration of flame and temperature is high, making it difficult to disperse quickly, and patients cannot leave the scene immediately. Moreover, in an enclosed space, incomplete combustion produces a large amount of carbon monoxide and other toxic gases, causing patients to become poisoned and unconscious, and in severe cases, asphyxiation can occur. During explosion and fire, high temperature, high pressure, high-speed airflow, and dense toxic gases can cause injury to the deep respiratory tract and lung parenchyma. In addition, standing or running and shouting can also be one of the causes of injury due to the inhalation of flame.

　　Pulmonary edema is the main pathological change in aspiration injury. Aspiration injury causes lung injury, which is generally considered to be mediated by free radicals, primarily initiated by oxygen free radicals. After lung injury, there are changes in vascular permeability and pulmonary edema, with a large amount of fluid entering the pulmonary interstitium due to damage to the pulmonary capillaries. At the same time, the bronchial veins are also severely damaged, and the fluids from these two pathways accumulate in the interstitium, forming interstitial edema. When the interstitial fluid further increases, increased hydrostatic pressure or the participation of other factors can lead to the destruction of the barrier function of the alveolar wall, with interstitial fluid entering the alveoli to form alveolar edema. After aspiration injury, plasma protein decomposition and leakage through the vascular wall cause a decrease in plasma colloid osmotic pressure, and an increase in interstitial osmotic pressure can also promote pulmonary edema.

　　Aspiration injury refers to chemical injury to the respiratory tract caused by inhaling toxic smoke or chemical substances. Severe cases can directly damage the lung parenchyma. It often occurs in large areas, especially in patients with burns to the head and face. Aspiration injury is divided into three categories according to the severity of the condition: mild, moderate, and severe. Below, let's specifically understand the symptoms of aspiration injury:

　　Mild aspiration injury:Refers to the injury above the glottis, including the nose, pharynx, and glottis. Clinical manifestations include pain in the nasopharynx, cough, increased saliva, and difficulty swallowing; local mucosal congestion, swelling, or formation of blisters, or mucosal erosion and necrosis. Patients do not have hoarseness or dyspnea, and pulmonary auscultation is normal.

　　Moderate aspiration injury:Injury above the tracheal prominence, including the pharynx and trachea. Clinical manifestations include irritative cough, hoarseness, dyspnea, sputum containing carbon particles and desquamated tracheal mucosa, laryngeal edema leading to airway obstruction, and inspiratory stridor. Pulmonary auscultation shows weakened or rough breath sounds, and occasionally wheezing and dry rales. Patients often have concurrent tracheitis and aspiration pneumonia.

　　重度吸入性损伤：重度吸入性损伤，伤后2天内为呼吸功能不全期。其主要表现呼吸困难，一般持续4～5天后，渐好转或恶化致呼吸衰竭而死亡。呼吸困难是由于广泛支气管损伤或含有肺实质损伤，引起通气、换气障碍，通气与血流灌注比例失调，导致进行性低气血症，血PaC2

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　　How to prevent inhalation injuries

　　Inhalation injuries are related to the environment causing the injury. Severe symptoms can directly damage the pulmonary substance, so everyone needs to understand the preventive methods.

　　Preventive measures for inhalation injuries

　　1. Open the channels connected to the non-smoke area outside to keep the indoor air sufficiently oxygenated.

　　2. Cover your mouth and nose with a moist towel of a certain thickness. If you can't find a wet towel, you can use other cotton fabrics as an alternative, which can reach a smoke removal rate of 60% to 100% and can filter out 10% to 40% carbon monoxide.

　　3. When escaping from the smoke and fire, if the smoke is not too dense, you can bend over to walk; if the smoke is dense, you must crawl on the ground with your face close to the ground within 30 centimeters. The smoke rises, and people should go down, and try to keep the body close to the ground when passing through dense smoke.

　　What laboratory tests need to be done for inhalation injuries

　　There are many diagnostic methods for inhalation injuries, and combining multiple methods can make the diagnosis more accurate. The commonly used examination methods are as follows:

　　1. X-ray examination

　　2. Special examination, it was previously believed that X-rays had no diagnostic significance for inhalation injuries. However, Wang Tianyi et al. (1980) and Yang Zhiyi et al. (1982) believed, based on animal experiments and clinical observations, that taking a right anterior oblique X-ray film within 2 to 6 hours after injury shows obvious tracheal stenosis, with speckled shadows in the trachea, reduced transmittance, irregular mucosa, and early signs of tracheal stenosis, which can be considered as corresponding X-ray changes. During pulmonary edema, there are disseminated, glassy shadows, interlobar shadows, dilated hilum, linear or crescent-shaped shadows; during pulmonary infection, central infiltrative shadows or diffuse and dense infiltrative shadows can be seen; sometimes, the increased transparency due to compensatory emphysema, as well as the shadow of pneumothorax caused by alveolar rupture or bullous emphysema, can be observed.

　　(1) Fiberoptic bronchoscopy examination

　　Fiberoptic bronchoscopy can directly observe the degree of injury to the pharynx, vocal cords, trachea, and bronchial mucosa, and determine the site of injury. Because it can take samples, drain, and wash within the airway, it is also a treatment tool. Dynamic observation through fiberoptic bronchoscopy can understand the outcome of the evolution of the lesion.

　　⑵ Scoring method for desquamated cell counting

　　Ambiavagar first reported in 1974 about observing the changes in various cell morphology and structure in bronchial secretions, as well as the presence of smoke particles, to diagnose the presence of inhalation injury. After inhalation injury, the morphology and structure of ciliated cells produce variations including cilium shedding, end plate disappearance, cytoplasm showing waxy azurophilic staining, and nucleus condensation. In severe cases, they may rupture or dissolve.

　　3. Pulmonary function examination

　　⑴ Blood gas analysis

　　After inhalation injury, PaO2 decreases to varying degrees, most of which are below 8kPa (60mmHg). For burn patients with similar burn areas but without inhalation injury, PaO2 is generally >10.67kPa (80mmHg). The PaO2/FIO2 ratio decreases (normal >53.2kPa), A-aDO2 increases early, and the degree of increase can be used as a predictor of prognosis. If PaO2 decreases progressively and A-aDO2 increases significantly, it indicates severe illness and poor prognosis.

　　⑵ Pulmonary function testing

　　They are more sensitive to low-position inhalation injury. This includes the first second of time vital capacity (FEV1), maximum vital capacity (FVC), J maximum expiratory flow-volume curve (MEFV), peak flow, flow rate at 50% vital capacity, and respiratory motor function (lung compliance, airway force, lung resistance, etc.). After severe inhalation injury, it involves small airways and lung parenchyma, increases airway resistance, the peak flow at 50% vital capacity can drop to 41.6±14.3%, lung compliance decreases, lung resistance significantly increases, MEFV significantly lower than normal values, and FEV1 and FVC appear abnormally earlier. These changes are due to airway obstruction, so pulmonary function tests are of certain significance in predicting the development of the disease.

　　Inhalation injury refers to chemical injury to the respiratory tract caused by inhaling toxic smoke or chemicals, which can directly damage the lung parenchyma in severe cases. After inhalation injury, while timely treatment is being given, attention should be paid to dietary adjustment, which is helpful for early recovery.

　　1. Easy-to-digest liquid high-protein diet

　　Diet should be colorful, fragrant, and tasty to increase the patient's appetite. In addition to the main dishes of three meals a day, milk, eggs, casein, soy milk can be provided between meals according to the patient's nitrogen balance and overall nutritional status, and try to achieve less meals and more snacks.

　　2. Ensure adequate water intake and vitamin supplementation

　　Such as mung bean soup, vegetable soup, honey water, watermelon juice, tomato juice, pear juice, and so on.

　　3. Avoid irritants

　　Burn patients are very sensitive to irritants, and consuming them can make the wound difficult to heal and cause edema. Common irritants include pork head meat, dog meat, deer meat, crucian carp, coriander, garlic sprouts, and chives.

　　4. Avoid coarse fibers and gas-producing foods

　　Common foods include bamboo shoots, bamboo sprouts, chives, celery, pineapples, and so on. These foods can cause bloating and affect digestion when consumed by burn patients with low gastrointestinal function.

　　The treatment methods for inhalation injury are relatively limited, as they involve metabolic and internal environment disorders, pulmonary functional pathophysiology and physiological changes, and often accompany other injuries. Therefore, the treatment principle is still to provide symptomatic treatment according to the stage changes of the disease course.

　　1. Fluid therapy:In cases of severe burns combined with inhalation injury, if fluid resuscitation is not given in a timely and reasonable manner to quickly restore tissue blood perfusion, it will cause hypoxic injury to various organs, including the lungs. This hypoxic injury caused by poor perfusion can further aggravate the occurrence and development of pulmonary edema after severe inhalation injury.

　　Clinical observations show that severe inhalation injury patients often develop significant pulmonary edema shortly after the injury, before fluid resuscitation. The occurrence of this pulmonary edema is unrelated to fluid resuscitation; on the contrary, if fluid resuscitation treatment is given promptly and shock is corrected in time, it can reduce pulmonary hypoxic injury and prevent the acceleration of the occurrence and development of pulmonary edema.

　　Animal experiments show that after severe steam inhalation injury, the degree of decrease in plasma volume and cardiac output is equivalent to that of body surface burn of 30% of the total body surface area. It can be seen that the fluid loss in patients with body surface burn and inhalation injury should not be less than that in patients with the same area of body surface burn.

　　The fluid treatment for patients with inhalation injury should not reduce the fluid volume. At the same time, it is more important to closely monitor cardiac and pulmonary function, in addition to observing urine output, blood pressure, heart rate, consciousness, blood gas analysis, and acid-base metabolism, central venous pressure should also be measured.

　　2. Tracheal intubation and tracheotomy:The number of patients undergoing tracheal intubation in clinical practice is increasing. Each tracheal intubation should not exceed 30s, and it should be performed under local anesthesia, using sedative drugs. The optimal tube placement time is 3-4 days. If edema occurs below the epiglottis, severe airway obstruction will occur, and tracheotomy should be performed.

　　3. Drug treatment:0.25-0.5g of aminophylline is added to 20-40ml of normal saline for intravenous injection; for severe bronchospasm, 40mg of dexamethasone is added, injected intravenously twice a day.

　　4. Oxygen inhalation:Low-flow oxygen should be inhaled.

　　5. Nebulized inhalation:Humidify the airways, promote the excretion of airway secretions, and prevent secondary pulmonary infections.