Irritant gas inhalation injury is the result of inhalation of gases which, when inhaled, dissolve in the water of the respiratory tract mucosa and cause an inflammatory response. Irritant gas exposures predominantly affect the airways, causing tracheitis, bronchitis, and bronchiolitis manifested by cough, hemoptysis, wheezing, retching, and dyspnea. Some less soluble gases are absorbed and have systemic effects. Diagnosis is by identification of the inhaled gas, the duration of exposure, and the results of chest x-ray and assessment of oxygenation. Treatment includes removal from exposure, supportive care, and additional measures depending on the specific intoxicant and severity.
(See also Pulmonary Chemical Warfare Agents and Overview of Environmental and Occupational Pulmonary Disease.)
Potentially hazardous substances can be inhaled as gases, fumes, vapors, mists, aerosols, and smoke. Airborne toxicants can injure the respiratory tract (local effects) and can also cause systemic injury. Most irritant gases are soluble in water and cause the abrupt onset of irritative symptoms at the mucosal surfaces they contact. These symptoms, which include lacrimation, rhinorrhea, and burning of the mouth and face, can serve as warning signs to move away from the exposure if possible. Gases that are less soluble in water have poor warning properties.
In addition to exposures in occupational settings, clinicians should be aware of the potential for exposure in other settings. A common potential household exposure involves mixing household ammonia with cleansers containing bleach, leading to the release of the irritant gas chloramine.
Acute Exposure to Irritant Gas
Acute exposure to high concentrations of toxic gas over a short time is characteristic of industrial accidents, such as those resulting from a faulty valve or pump in a gas tank or occurring during gas transport. The exposure can be localized to specific workers at a worksite or affect a larger group of people. Notable examples of accidents causing widespread exposure were the release of methyl isocyanate from a chemical plant in Bhopal, India in 1984, resulting in thousands of deaths, and the East Palestine, Ohio, train derailment in 2023 that released hydrogen chloride, phosgene and other chemicals in the small town.
Respiratory damage is related to the concentration of the gas, its water solubility, and the duration of exposure. High-intensity exposures can lead to clinical effects within seconds, minutes, or hours, depending on the actual dose of exposure. In addition to acute effects, there can also be long-term effects.
More water-soluble gases (eg, chlorine, ammonia, sulfur dioxide, hydrogen chloride) dissolve in the upper airway and immediately cause mucous membrane irritation, which may alert people to the need to escape the exposure. Higher levels of exposure, such as when escape from the gas source is impeded, can permanently damage the upper airways, causing cough and laryngospasm, and the lower respiratory tract, causing pulmonary edema and acute respiratory distress syndrome (ARDS).
Less soluble gases (eg, nitrogen dioxide, phosgene) generally spare the upper airways. These agents are less likely to cause early warning signs; injury to the lower respiratory tract often has a lag of multiple hours before symptoms develop.
Complications
Short-term, high-intensity exposure to certain irritant gases can also lead to longer-term effects, such as the development of reactive airway dysfunction syndrome (RADS).
In severe exposures, the most serious immediate potential complication is acute respiratory distress syndrome (ARDS), which usually develops rapidly following significant lower airway exposure, but can be delayed as long as 24 hours.
Patients with significant lower airway involvement may develop bacterial infection.
Bronchiolitis obliterans is a less frequent complication of exposure to certain toxic gases, (eg, nitrogen dioxide and also ammonia and sulfur dioxide), occurring 1 to 3 weeks following initial injury. Bronchiolitis obliterans with organized pneumonia can ensue when granulation tissue accumulates in the terminal airways and alveolar ducts during the body’s reparative process. A minority of these patients develop late pulmonary fibrosis.
Symptoms and Signs of Acute Exposure to Irritant Gas
The severity of symptoms depends on the extent of the exposure as well as the properties of the specific irritant gas.
Soluble irritant gases cause severe burning and other manifestations of irritation of the eyes, nose, throat, trachea, and major bronchi. Severe cough, hemoptysis, wheezing, retching, and dyspnea are common. The upper airway may be obstructed by edema, secretions, or laryngospasm.
Nonsoluble gases cause fewer immediate irritative upper airway symptoms but can have delayed effects once they penetrate to the lower airways.
Diagnosis of Acute Exposure to Irritant Gas
History of exposure
Chest x-ray
The history is usually sufficient to identify an irritant gas exposure as the cause of respiratory symptoms and signs. Pertinent features of the history include the specific toxicant or toxicants involved in the exposure (if available), duration of the exposure, description of the physical space in which the exposure occurred, and whether loss of consciousness occurred.
During the initial evaluation, patients should have a chest x-ray and assessment of oxygenation with pulse oximetry. Chest x-ray has low sensitivity for inhalation injury, though findings of patchy or confluent alveolar consolidation usually indicate pulmonary edema and are associated with more severe injury.
Inhalational injury can occur anywhere along the airway passages and can be classified based on the primary area of injury such as upper airway, the tracheobronchial system, or lung parenchyma. Direct visualization of the airways can help determine the severity of injury and confirm diagnosis.
If there are significant persistent symptoms following the exposure, pulmonary function testing and chest CT can be helpful.
Pulmonary function tests are not usually performed in the acute setting but may be helpful if symptoms persist. Obstructive abnormalities are most common, but restrictive abnormalities can predominate after exposure to high doses of chlorine.
Treatment of Acute Exposure to Irritant Gas
Removal from exposure
Supportive respiratory care
Mechanical ventilation when indicated
Treatment depends on the nature and severity of the exposure. Supportive respiratory care is a cornerstone of treatment. Patients should initially be moved into fresh air and given supplemental oxygen. Treatment is directed toward ensuring adequate oxygenation and ventilation in an appropriate setting. Patients who experience high-intensity exposure are often managed initially by first responders and then transported to a hospital for further evaluation and treatment.
Bronchodilators and oxygen therapy may be used in patients with less severe exposure.
endotracheal intubation or tracheostomy, and mechanical ventilation.
Patients with suspected lower airway involvement due to high-dose exposure or exposure to a non-water soluble gas should be observed for development of ARDS. High-quality data on efficacy of corticosteroids for ARDS induced by inhalational injury are lacking.
After the acute phase has been managed, patients with persistent symptoms should be monitored for the development of reactive airways dysfunction syndrome, bronchiolitis obliterans with or without organized pneumonia, and pulmonary fibrosis.
Prognosis for Acute Exposure to Irritant Gas
Prognosis depends on the nature and severity of the exposure. Most patients with less severe exposure recover fully, but patients can develop persistent lung injury with reversible airway obstruction (reactive airways dysfunction syndrome) or, less frequently, bronchiolitis and/or bronchiectasis.
In patients with severe exposure leading to ARDS, mortality is high.
Prevention of Acute Exposure to Irritant Gas
Care in storing, handling, and transporting gases and chemicals is the most important preventive measure.
The availability of adequate respiratory protection (eg, gas masks with a self-contained air supply) for rescuers is also very important; rescuers without protective gear who rush in to rescue a patient exposed to an irritant gas are often injured themselves.
Chronic Exposure to Irritant Gas
In addition to more acute exposures, such as those associated with accidents, repeated exposures to lower concentrations can also have adverse health effects.
Lower concentration chronic exposures occur more commonly than major accidents. Exposure to irritant gases, such as chlorine released from bleach, may lead to irritant-induced asthma.
In the absence of a clear-cut exposure, diagnosing chronic exposures may require a higher degree of clinical suspicion to identify. History should include review of home and workplace environments.
Treatment involves elimination of exposure and symptomatic treatment for irritant upper airway symptoms.
Exposure to Smoke
Smoke is a complex mixture of gases and particulates. Factors influencing the components of smoke are the type of material or materials being consumed by fire, the temperature of combustion, and the amount of oxygen present. Irritant gases are frequently present in smoke as well as other gases, such as carbon monoxide and particulates. See Smoke Inhalation for details on diagnosis and treatment.
Key Points
The site and extent of inhalational injury is primarily dependent upon the water solubility of the gas and the magnitude of exposure.
Diagnosis of acute exposure is based primarily on history, with further testing depending on the clinical severity.
Treatment depends on the nature and severity of the exposure. Low severity exposures can often be managed supportively, whereas severe cases may require emergency treatment and critical care.
