Hydrocarbons are organic compounds that consist of hydrogen and carbon. They are quite ubiquitous in society and are present in many common household and occupational products, for example, in motor fuel, paint thinner, cleaning agents, lotion, and industrial solvents. Unfortunately, these products are also used as agents of abuse and typically are inhaled for their euphoric effects. Inhalation is made possible by the volatility of these substances.[1]

Serious toxicity and death can be associated with hydrocarbon exposure through inhalation, ingestion, or aspiration. Pulmonary toxicity is most common, however cardiovascular, nervous, and gastrointestinal systems can all be affected.

Hydrocarbons are a primary energy source in modern society. They are derived mainly from petroleum (kerosene, gas, naphtha) or wood (turpentine, pine oil). They can be found in liquid, gas, or solid form depending on their properties. All hydrocarbons can be toxic, but aromatic (ring-shaped) and halogenated hydrocarbons typically have more severe toxicity.

Toxicity occurs in various ways including through inhalation, ingestion, aspiration, and dermal exposure. Frequently, these exposures occur during attempted recreational use of the substances and sometimes for self-injurious behavior. Three inhalation methods for recreational uses are common. These include “huffing” or breathing through a rag soaked with the inhalant, “bagging,” which means repeatedly inhaling deeply from a bag filled with the hydrocarbon, and “sniffing” or directly inhaling the hydrocarbon through the nostrils. Most commonly abused hydrocarbons are paints, solvents, and gasoline.[2]

Hydrocarbon toxicity affects more than 30,000 Americans per year.  Approximately 20 deaths per year are attributed to hydrocarbon toxicity. Children younger than five years old as well as adolescents are disproportionately affected. Abuse is becoming increasingly common with an estimated 20% of middle and high school students reported having tried these volatile substances. The most common complications are pneumonitis followed by central nervous system and cardiovascular effects.[3][2][4][5]

Multiple factors determine the toxicity of hydrocarbons. These include physical and chemical characteristics, dose and concentration, additives, and routes of exposure. Aspiration risk is directly related to the physical characteristics such as viscosity, surface tension, and volatility. Viscosity is a measurement of the resistance to flow, surface tension refers to the ability of particles to cohere together, and volatility is the tendency for a liquid to change to gas. Lower viscosity, lower surface tension, and higher volatility all increase the risk of aspiration and subsequently, increase the risk of toxicity. These specific properties allow for easy flow, diffuse spread on mucosa and lung surfaces, and ability to vaporize at body temperature, respectively. Inhalation or ingestion can both allow for easy absorption of the hydrocarbon which can lead to systemic toxicity.[6]

The pulmonary system is most commonly affected by inhalation or aspiration. Depending on the specific substance's characteristics or significant systemic absorption, multiple systems in the body may be affected by these same routes of exposure. Pulmonary toxicity from inhalation or aspiration occurs from direct toxicity. Hydrocarbon pneumonitis is caused by the destruction of alveolar and capillary membranes as well as alteration of surfactant function and production.  This eventually can lead to ARDS due to increased vascular permeability and edema. Progression to necrotizing pneumonitis and hemorrhagic pulmonary edema is ultimately possible. Rarer pulmonary complications include lung necrosis, pneumothorax, pneumatocele, or bronchopleural fistula. Ultimately, hypoxia develops secondary to ventilation/perfusion mismatch, shunt formation, and direct displacement of alveolar oxygen.[7][8]

Cardiac toxicity is also a possibility following hydrocarbon exposure. Life-threatening dysrhythmias may occur such as ventricular tachycardia or fibrillation. “Sudden sniffing death syndrome” has been described in hydrocarbon abusers which occurs shortly after exposure often without any preceding symptoms. This typically occurs after a patient is “excited” while they are huffing or bagging leading to a large surge of catecholamines. This large surge of catecholamines, although typically not an issue, causes risk of arrhythmias due to increased myocardium sensitization, a side effect of hydrocarbons.[9][10]

The primary CNS effect associated with hydrocarbon toxicity is a decreased level of consciousness. Multiple pathways ultimately lead to this decreased level of consciousness. Many hydrocarbons cross the blood-brain barrier causing direct toxicity. There are also indirect CNS effects as a result of severe hypoxia from lung injury or oxygen displacement or hypercarbia from the act of rebreathing into a bag.  Prolonged and recurrent exposure to hydrocarbons can lead to white matter degeneration as well as peripheral demyelination.[1]

Other systems are also commonly affected. Hydrocarbons are gastrointestinal (GI) irritants which lead to burning abdominal pain, vomiting or even gastric perforation; however, this is more common with ingestion as opposed to inhalation. Hepatic damage, especially from chlorinated hydrocarbons, is not uncommon and appears to have a similar course as that of acetaminophen hepatotoxicity. Toluene, an aromatic hydrocarbon, has a propensity to cause renal tubular acidosis or severe hypokalemia, similar to hypokalemic periodic paralysis. Some specific hydrocarbons also are associated with hematologic disorders, including benzene and naphthalene. Methemoglobinemia and delayed carboxyhemoglobinemia are specifically associated with exposure to hydrocarbons containing amines and methylene chloride, respectively. Rashes may be noted over the face or on the hands of habitual inhalation users secondary to irritation or sensitization. Dermatitis, cellulitis, and soft tissue necrosis are also possible depending on the method of exposure.[11][12][13]][14]