- Author: Michael D Levine, MD; Chief Editor: Asim Tarabar, MD more...
Hydrocarbons are a heterogenous group of organic substances that are primarily composed of carbon and hydrogen molecules. They are quite abundant in modern society. Some of the most commonly ingested hydrocarbons include gasoline, lubricating oil, motor oil, mineral spirits, lighter fluid/naphtha, lamp oil, and kerosene. Other common sources of hydrocarbons include dry cleaning solutions, paint, spot remover, rubber cement, and solvents. In addition, many volatile substances that contain hydrocarbons (eg, glue, propellants) are commonly abused for their euphoric effects.
Hydrocarbons can be classified as being aliphatic, in which the carbon moieties are arranged in a linear or branched chain, or aromatic, in which the carbon moieties are arranged in a ring. Halogenated hydrocarbons are a subgroup of aromatic hydrocarbons, in which one of the hydrogen molecules is substituted by a halogen group. The most important halogenated hydrocarbons include carbon tetrachloride, trichloroethylene, tetrachloroethylene, trichloroethane, chloroform, and methylene chloride.
The hydrocarbons can be derived from either petroleum or wood. Petroleum distillates include kerosene, gasoline, and naphtha, whereas wood-derived hydrocarbons include turpentine and pine oil. The length of the chains as well as the degree of branching determine the phase of the hydrocarbon at room temperature; most are liquid, but some short-chain hydrocarbons (eg, butane) are gas at room temperature, whereas other long-chain hydrocarbons (eg, waxes) are solid at room temperature.
Toxicity from hydrocarbon ingestion can affect many different organs, but the lungs are the most commonly affected organ. The chemical properties of the individual hydrocarbon determine the specific toxicity, while the dose and route of ingestion affect which organs are exposed to the toxicity. Unlike the aromatic or aliphatic hydrocarbons, the halogenated hydrocarbons tend to cause a wider range of toxicity.
The recreational use of inhaling hydrocarbons and other volatile solvents for the purposes of creating a euphoric state is becoming increasingly common. Several methods are used for this abuse, including "sniffing" (directly inhaling vapors), "huffing" (placing a hydrocarbon-saturated rag over the mouth and nose and then inhaling), or "bagging" (inhaling via a plastic bag filled with hydrocarbon vapors).
The toxicity of hydrocarbons is directly related to their physical properties, specifically the viscosity, volatility, surface tension, and chemical activity of the side chains. The viscosity is a measure of resistance to flow and is measured in Saybolt Seconds Universal (SSU). Substances with a lower viscosity (SSU < 60, eg, turpentine, gasoline, naphtha) are associated with a higher chance of aspiration. The surface tension is a cohesive force created by van der Waals forces between molecules and is a measure of a liquid's ability to "creep." Like the viscosity, the surface tension is also inversely related to aspiration risk; the lower the viscosity, the higher the risk of aspiration. The viscosity is the single most important chemical property associated with the aspiration risk.
Volatility is the tendency for a liquid to change phases and become a gas. Hydrocarbons with a high volatility can vaporize and displace oxygen, which can lead to a transient state of hypoxia. Not surprisingly, the degree of volatility is directly related with the risk of aspiration. The amount of hydrocarbon ingested has not consistently been linked to the degree of aspiration and hence pulmonary toxicity.
Toxicity from hydrocarbon exposure can be thought of as different syndromes, depending on which organ system is predominately involved. Organ systems that can be affected by hydrocarbons include the pulmonary, neurologic, cardiac, gastrointestinal, hepatic, renal, dermatologic, and hematologic systems. The pulmonary system is the most commonly involved system.
Pulmonary complications, especially aspiration, are the most frequently reported adverse effect of hydrocarbon exposure. While most aliphatic hydrocarbons have little GI absorption, aspiration frequently occurs, either initially or in a semidelayed fashion as the patient coughs or vomits, thereby resulting in pulmonary effects. Once aspirated, the hydrocarbons can create a severe pneumonitis.
Hydrocarbon pneumonitis results from a direct toxic affect by the hydrocarbon on the lung parenchyma. The type II pneumocytes are most affected, resulting in decreased surfactant production. This decrease in surfactant, results in alveolar collapse, ventilation-perfusion mismatch, and hypoxemia. Hemorrhagic alveolitis can subsequently occur, which peaks 3 days after ingestion. The end result of hydrocarbon aspiration is interstitial inflammation, intra-alveolar hemorrhage and edema, hyperemia, bronchial necrosis, and vascular necrosis. Rare pulmonary complications include the development a pneumothorax, pneumatocele, or bronchopleural fistula.
CNS toxicity can result from several mechanisms, including direct injury to the brain or indirectly as a result of severe hypoxia or simple asphyxiation.
Many of the hydrocarbons that affect the CNS directly can make their way across the blood-brain barrier because certain hydrocarbons are highly lipophilic. In addition, for individuals who are huffing or bagging, the act of rebreathing can result in hypercarbia, which can contribute to decreased level of arousal.
Prolonged abuse of hydrocarbons can result in white matter degeneration (leukoencephalopathy) and atrophy.[6, 7] In addition, prolonged exposure to certain hydrocarbons (eg, n -hexane or methyl-n -butyl ketone [MnBK]) can result in peripheral neuropathy, blurred vision, sensory impairment, muscle atrophy, and parkinsonism.
Exposure to hydrocarbons can result in cardiotoxicity.
Most importantly, the myocardium becomes sensitized to the effects of catecholamines, which can predispose the patient to tachydysrhythmias, which can result in syncope or sudden death.
Many of the hydrocarbons create a burning sensation because they are irritating to the GI mucosa. Vomiting has been reported in up to one third of all hydrocarbon exposures.
The chlorinated hydrocarbons, in particular carbon tetrachloride, are hepatotoxic. Usually, the hepatotoxicity results after the hydrocarbon undergoes phase I metabolism, thereby inducing free radical formation. These free radicals subsequently bond with hepatic macromolecules and ultimately cause lipid peroxidation. This metabolite creates a covalent bond with the hepatic macromolecules, thereby initiating lipid peroxidation.
The common histopathologic pattern is centrilobular (zone III) necrosis.
Liver function test results can be abnormal within 24 hours after ingestion, and clinically apparent jaundice can occur within 48-96 hours.
Methylene chloride, a hydrocarbon commonly found in paint remover, is metabolized via the P450 mixed function oxidase system in the liver to carbon monoxide (CO). Unlike other cases of CO exposure, with methylene chloride, CO formation can continue for a prolonged period of time.
Chronic exposure to toluene, an aromatic hydrocarbon, can result in a distal renal tubular acidosis and present with an anion gap acidosis (see the Anion Gap calculator). A patient may have chronic exposure either via an occupational environment or by repeated recreational inhalation.
Prolonged exposure to certain aromatic hydrocarbons (especially benzene) can lead to an increased risk of aplastic anemia, multiple myeloma, and acute myelogenous leukemia. In addition, hemolysis has been reported following the acute ingestion of various types of hydrocarbons.
In 2012, 31,031 cases of hydrocarbon poisoning were reported to US poison control centers. Of those, 13,422 were in patients aged 19 years or younger.
In developing nations, kerosene is implicated in approximately one third of pediatric poisonings.
In 2012, 18 deaths due to hydrocarbons were reported to US poison control centers. However, several other deaths are classified as being due to "chemicals, cleaning substances, fumes/gases/vaporizers," and "pesticides." Thus, the true number is probably slightly higher. In addition, the poison control data are widely known to be an underestimate of the true incidence because of underreporting.
Proportionately, more fatalities are associated with children younger than 5 years who often accidentally ingest hydrocarbons, and among adolescents, who are more likely to abuse volatile hydrocarbons.
Inhalant abuse is becoming increasingly common among adolescents. It is estimated that approximately 20% of students in middle school and high school have abused volatile substances.
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