“Smoke inhalation” is a generic term that refers to potential exposure to a wide variety of substances because of the complex chemistry of heat decomposition. Inhaled substances may directly injure the pulmonary epithelium at various levels of the respiratory tract, leading to a wide range of disorders from tracheitis and bronchiolitis to pulmonary edema. Thermal injuries are typically limited to upper airways; however, injury below the vocal cords can occur in steam inhalation. The fumes may also be absorbed, resulting in systemic toxicity. Under many exposure situations, both routes may be common. Thus, determining the mechanism of respiratory insufficiency, whether it is a result of direct injury of the respiratory tract or systemic toxicity, is difficult. Accordingly, it is best to classify inhaled agents as both airway irritants and systemic toxins.
Many factors, such as concentration of inhaled toxin, duration of exposure, and whether exposure occurred in an enclosed space, determine the degree of injury after acute inhalation exposure, as well as other factors such as particle size and water solubility. The degree of injury also is affected by age of the patients, allergic or non-allergic bronchospastic response, exertional state or metabolic rate of the victim, history of smoking, and those with underlying lung debilitating illness.
Symptoms of inhalation burns begin with rapidly developing signs of upper airway irritation that are accompanied by eye and mucous membrane irritation. In severe exposures, progressive coughing, wheezing, or stridor may result in upper airway obstruction. That being said, the rate at which these symptoms appear can be influenced by the solubility of the chemicals inhaled. Inhaled toxins of smaller particle size or lower solubility such as ozone, fluorine, or oxides of nitrogen may reach the lower respiratory tract, resulting in delayed onset of the symptoms. Following mild exposure, gases with intermediate solubility (e.g. chlorine) may lead to early irritating symptoms. In massive exposure, upper airway obstruction may lead to death due to asphyxiation or alveolar destruction.
Exposure to heat, particulate matter, and toxic gases are considered in the exposure to smoke. Closed-space fires and conditions that cause unconsciousness are often the reason for inhalation injuries. Between 20% and 30% of burn victims suffer from pulmonary complications. Tracheobronchial damage and pulmonary complications are an important cause of morbidity and mortality.
Since there may be a delay between the onset of symptoms after inhalation, it may be difficult to assess a patient for inhalation burns. Soot around the nose and mouth, singed nasal hairs, or any facial burns should give a high index of suspicion. The entire respiratory tract can be affected by smoke inhalation from fires. Small particles can easily reach the terminal bronchioles causing an inflammatory reaction, leading to bronchospasm. Therefore, any suspicion of chemical and/or thermal inhalation injury should be evaluated and treated aggressively prior to the onset of symptoms.
References:
Gorguner, Metin and Akgun, Metin. (2010). Acute Inhalation Injury. The Eurasian Journal of Medicine, 42 (1), 28-35. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4261306/.
Lafferty, Keith A. (2017). Smoke Inhalation Injury. Medscape. Retrieved from https://emedicine.medscape.com/article/771194-overview.
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