Irritant gases have direct irritating effects on the respiratory mucosa, eyes and skin. After inhalation, mild cases may show symptoms of upper respiratory tract irritation or bronchitis, while severe cases may produce toxic pneumonia or toxic pulmonary edema, and may develop into acute respiratory distress syndrome (ARDS). The severity of the damage mainly depends on the physical and chemical properties of the inhaled gas, its concentration and the length of exposure time.
Common irritating gases include: ① Acids: inorganic acids, such as sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid; organic acids, such as formic acid, acetic acid, propionic acid, oxalic acid, and acrylic acid; ② Acid-forming oxides: sulfur dioxide, sulfur trioxide, nitrogen dioxide, and nitrogen tetroxide; ③ Ammonia and amines: ammonia, methylamine, ethylamine, and acrylamine; ④ Phosgene; ⑤ Halogenated hydrocarbons: octafluoroisobutylene, fluorophosgene, polytetrachloroethylene cracking gas, methane, and chloropicrin; ⑥ Vinegars: dimethyl sulfate, methyl acetate, and the like; ⑦ Aldehydes: formaldehyde, acetaldehyde, and acrolein; ⑧ Ethers: chloromethyl methyl ether, and the like; ⑨ Metal and metalloid compound smoke: such as carbonyl nickel and cadmium oxide.
According to the chemical properties of irritating gases, they can be divided into: 1. Highly water-soluble irritating gases, such as chlorine, ammonia, and sulfur dioxide. This type of poison has a high solubility in water and dissolves quickly on the moist tissue surface of the eyes and upper respiratory tract to form acidic or alkaline substances. The clinical manifestations are mainly irritation symptoms, and there is often no incubation period when pulmonary edema occurs. 2. Low water-soluble irritant gases, such as nitrogen oxides, phosgene, dimethyl sulfate, and carbonyl nickel. Due to their low solubility, the irritation to the upper respiratory tract is weak, the amount of gas inhaled is relatively increased, and it is easy to enter the deep respiratory tract, causing toxic pneumonia and pulmonary edema. The possibility of onset has a certain incubation period. The incubation period shortens with the increase of the amount of inhaled poison, the concentration of the poison, and the contact time, but is inversely proportional to the solubility.
【Clinical manifestations】
(i) Toxic respiratory inflammation is mostly caused by highly water-soluble irritant gases. Mucosal irritation symptoms appear immediately after inhalation. Clinical manifestations include respiratory symptoms such as rhinitis, pharyngitis, glottic edema, and tracheal and bronchitis. Long-term and repeated inhalation of low-concentration irritating gases can cause chronic rhinitis, bronchitis, bronchial asthma, and chronic obstructive pulmonary disease (COPD), which manifests as dry nose, itchy nose, hyposmia, dry throat, sore throat, chest tightness, shortness of breath, cough, sputum, and occasionally blood in the sputum. Chronic asthmatic bronchitis is difficult to recover.
(II) Toxic pneumonia Irritating gases enter the deep respiratory tract and reach the alveoli, which can easily cause inflammatory reactions in the lung parenchyma. Inhalation of smoke and dust such as manganese and cadmium and choking of gasoline into the lungs cause pneumonia. Toxic pneumonia is mainly manifested by symptoms of upper respiratory tract irritation, chest tightness, chest pain, shortness of breath, severe cough, sputum, and sometimes blood in the sputum. Inhalation pneumonia caused by inhalation of gasoline is particularly prone to chest pain, which manifests as stabbing or knife-like pain on the affected side. Generally, the symptoms will be relieved after 4-5 days. The total white blood cell count and the proportion of neutrophils are increased, and can return to normal within 2-3 days. If the white blood cell count continues to increase, there is a possibility of secondary bacterial infection. X-ray signs may include local flake shadows and low-density dot-shaped shadows, thickened lung texture, irregular edges, and relatively clear upper lung fields.
(III) Toxic pulmonary edema and ARDS
After inhaling irritating gases with low water solubility, the mucosal irritation symptoms are relatively mild, with only choking, chest tightness and nausea, and few positive signs, only congestion of the pharynx and conjunctiva, and occasional dry rales. After disengagement, the above symptoms may be significantly alleviated or basically disappear (false recovery period), but after several hours to dozens of hours, the condition suddenly worsens, with chest tightness and coughing, and dyspnea, cyanosis, irritability, coughing pink foamy sputum, and diffuse wet rales in both lungs. Some patients have progressive dyspnea, which then develops into ARDS. If not rescued in time, respiratory and circulatory failure may endanger life.
After inhaling irritating gases with high water solubility, obvious symptoms of eye and upper respiratory tract mucosal irritation appear immediately, followed by symptoms and signs of pulmonary edema, which may develop into ARDS. Critically ill patients may have complications such as laryngeal edema, mediastinal emphysema, pneumothorax, and atelectasis. In the early stage of chest X-ray examination, blurred textures of both lungs, extensive reticular shadows or scattered fine-grained shadows, and reduced translucency of the lung fields can be seen. As the disease progresses, large uniform shadows with increased density or flake shadows of varying sizes and densities with blurred edges appear, which are widely distributed in both lung fields, and a few are butterfly-wing-shaped.
【Treatment】
Immediately leave the irritating gas environment.
Acidic gases can be inhaled by nebulization with 5% sodium bicarbonate solution; alkaline gases can be inhaled by nebulization with 3% boric acid solution to neutralize and relieve respiratory irritation symptoms.
If coughing is frequent and there are symptoms such as shortness of breath and chest tightness, 0.5% isoproterenol 1ml and dexamethasone 2mg can be used, and water can be added to 3ml for nebulization and inhalation. When necessary, symptomatic, expectorant, and anti-infective drugs can be used.
After inhaling irritating gases with low water solubility, even if the clinical manifestations are mild at the time, you should rest in bed, keep quiet, and observe closely for 72 hours. If there are symptoms such as shortness of breath and chest tightness, oxygen therapy should be given, generally with nasal cannula inhalation, oxygen flow rate 5-6L/min.
In case of pulmonary edema, inhale silicone defoaming agent (dimethyl silicone) to clear airway blisters and increase oxygen inhalation.
When ARDS occurs, pressurized oxygen or positive end-expiratory pressure breathing (PEEP) is used; glucocorticoids should be used early, in large quantities, and for a short period of time. Dexamethasone 20-40mg/d, or hydrocortisone 400-1000mg/d, or methylprednisolone 100-200mg/d are commonly used, generally for 3-5 days, and the dosage is reduced or discontinued after the condition improves. To prevent obliterative bronchiolitis or pulmonary fibrosis, it can be maintained for a certain period of time after the dose is reduced.
Scopolamine hydrobromide relaxes smooth muscles, reduces mucus secretion, and improves microcirculation. The usual dosage is 0.01-0.1 mg/kg, administered intravenously, once every 15-30 minutes, generally used 1-4 times, and has a certain effect on pulmonary edema and ARDS.
Critically ill patients should prevent suffocation, perform tracheotomy when necessary, correct acid-base imbalance and water and electrolyte disorders, and actively deal with complications such as lung infection, pneumothorax, and multiple organ failure.
