Acute Inhalation Injury - Causes, Symptoms, and Treatment

Introduction

Acute inhalation injury refers to the injury to the pulmonary epithelium. Various toxic substances cause acute inhalation injury. The level of injury depends on the type and amount of toxin inhaled. It can cause disorders like tracheitis and bronchiolitis to pulmonary edema. The inhaled toxins can get absorbed and result in systemic toxicity.

What Is Acute Inhalation Injury?

Inhaled toxins cause inhalation injury to the respiratory tract. The inhaled toxic substances injure the pulmonary epithelium. They cause cellular damage, changes in regional blood circulation and perfusion, obstruction of the airways, and release of proinflammatory cytokines and toxins. It also reduces mucociliary clearance and increases the risk of infection.

What Are the Causes of Acute Inhalation Injury?

Inhalation injury can be caused by inhaling chemical irritants, asphyxiants, burns, smoke inhalation, chemical warfare and riot control agents, toxic metals, and complex exposures.

Chemical Irritants - Inhaling chemical irritants from occupational and environmental areas can cause inhalation injury. The chemical irritants that cause injury are:

• Chlorine Gas - Chlorine gas is a common chemical irritant that causes inhalation injury. It is used as a disinfectant for drinking water and as a household bleaching agent. It causes acute injury to the upper and lower respiratory tract when inhaled. Chlorine gas damages the conjunctivae of the eyes and upper respiratory mucus membrane. It causes acute inflammation in the conjunctiva, nose, pharynx, larynx, trachea, and bronchi. It irritates the mucus membrane, and edema occurs secondary to arterial and capillary hyperemia. Pulmonary edema is a significant sign of pulmonary injury due to chlorine gas.

• Hydrogen Chloride - Hydrogen chloride is a pungent-smelling colorless gas. It is used for cleaning, pickling, electroplating metals, refining metal ores, leather tanning, and producing polymers and plastics. It irritates the mucus membranes of the nose, throat, and respiratory tract.

• Ammonia - Ammonia is a highly irritating gas. It is used in fertilizers. It causes eye, nose, and throat irritation. It results in bronchospasm, laryngospasm, laryngeal edema, and pulmonary edema. It causes chronic lung diseases like bronchitis, bronchiectasis, interstitial fibrosis, and impaired gaseous exchange.

• Hydrogen Fluoride - Hydrogen fluoride gas is a weak gas. However, it causes respiratory distress. It irritates the eyes, nose, and throat. It can cause chemical pneumonitis, pulmonary edema, and death.

• Sulfur Dioxide - It is produced from volcanoes. Burning poor-quality coal and petroleum can produce sulfur dioxide gas. It injures the larynx, trachea, bronchi, and alveoli. It causes burning of the eyes, nose, and throat, cough, chest pain, and tightness. Pharyngeal edema and pulmonary edema may develop. It causes bronchiolitis obliterans two to three weeks after exposure.

• Oxides of Nitrogen - Nitric oxide and nitrogen dioxide are toxic gases that cause inhalation injury. Silo fillers, firefighters, coal miners, welders, hockey rink workers, and chemical workers are exposed to these gases. It causes shortness of breath and cough if exposure is mild. High exposures can result in bronchospasm, pulmonary edema, toxic pneumonitis, and bronchiolitis.

• Phosgene - It is a highly toxic gas that was used during the first world war. It produces isocyanates, pesticides, dyes, and household substances. It causes chest pain, bronchospasm, hypoventilation, and bradycardia. Dyspnea and pulmonary edema can develop 24 hours after exposure.

• Hydrogen Sulfide - It is produced by the decomposition of organic matter and by industrial processes. Inhaling hydrogen sulfide gas affects the lower respiratory tract and causes cough, shortness of breath, and bronchial or lung hemorrhage.

Asphyxiants - Any gases at high concentrations are called asphyxiants. Asphyxiants are classified into simple asphyxiants and chemical asphyxiants. Simple asphyxiants displace oxygen from inhaled air and cause hypoxemia. Chemical asphyxiants like carbon monoxide and hydrogen cyanide interfere with oxygen delivery or utilization.

Burns and Smoke Inhalation - Heat, particulate matter, toxic gases, and closed-space fires can cause inhalation injuries. They result in tracheobronchial damage and cause pulmonary complications. Inhaling smoke can affect the terminal bronchioles and initiate an inflammatory reaction resulting in bronchospasm.

Chemical Warfare Agents - Mustard gas, phosgene, and chloropicrin were used during the first and second world wars. The current chemical warfare is derived from organophosphate pesticides. They cause bronchorrhea and bronchospasm. It causes lower respiratory tract irritation and results in pulmonary edema.

Toxic Metals - Cadmium and mercury are the common toxic metals that cause inhalation injury. Inhalation of fumes or vapors causes pneumonitis, metal fume fever, and organic dust toxic syndrome. It also causes cough and dyspnea.

Complex Exposures - Inhaling a complex mixture of toxic substances causes airway and diffuse interstitial lung lesions.

What Are the Effects of Acute Inhalation Injury?

The level of respiratory damage depends on the concentration of gas and its solubility. Inhaled gases affect the airways and cause tracheitis, bronchitis, and bronchiolitis. It causes permanent damage to the upper respiratory tract, lung parenchyma, and distal airways. Acute lung injury is caused by the disruption of the capillary-endothelial interface. The toxic substances damage the epithelium and induce the inflammatory response and destruction of pneumocytes. This results in fibroblastic proliferation, formation of hyaline membrane, tracheal remodeling, and lung fibrosis. Inhalation of toxins also causes respiratory distress. Burn and smoke inhalation impairs hypoxic pulmonary vasoconstriction, which is the vasoconstrictive response to hypoxia. This disrupts ventilation with perfusion.

What Are the Signs and Symptoms of Acute Inhalation Injury?

Inhalation injury causes the following signs and symptoms.

• Burning of eyes, nose, throat, and windpipe.

• Lacrimation, rhinitis, epistaxis, pharyngitis, and cough.

• Stridor, hoarseness, and dysphagia.

• Conjunctivitis, pharyngitis, laryngotracheitis, and expiratory wheezing.

• Edema in the nose, pharynx, and larynx.

• Headache, dizziness, and chest pain.

How Is Acute Inhalation Injury Treated?

The drugs which prevent inhalation injury are not available. Analgesics, oxygen therapy, and ventilator support are the standard treatment strategies. Corticosteroids and bronchodilators are given to treat bronchospasms and inflammation. Acute injury requires supportive treatment like airway protection, breathing, and circulation. The severe laryngeal injury requires intubation. Oxygen support is vital for inhalation injury.

Conclusion

Acute inhalation injury is a common respiratory condition caused by occupational or environmental factors. It can cause serious respiratory complications. However, it can be treated. Timely diagnosis and treatment can reduce the progression of injury and prevent complications. Studies are being carried out on developing pulmonary protective and reparative agents to treat mass inhalation injuries.