Irritant Gases ( Moderately Highly Water Soluble ) Irritant

mixture of suspended small particles, fumes, and gases. More than 400 toxic compounds have been demonstrated in the smoke of a typical house fire. Polyvinyl chloride, a component of many plastic goods, generates at least 75 different toxic products when burned. Of these toxic substances, carbon monoxide (CO) appears to be the most common fatal substance associated with fire victims. Thermal inhalation injuries are usually localized to the upper airway. Irritant gases, depending on their water solubility, affect either the upper or lower airway. Highly watersoluble agents such as ammonia, hydrogen chloride, and sulfur dioxide predominantly affect the upper airway. Their solubility directly correlates with rapid adverse upper airway symptoms. Agents with lower water solubility, such as phosgene and nitrogen dioxide, which do not produce immediate irritation, will be inhaled deeper in the pulmonary system and result in injury to the alveoli; victims typically have delayed noncardiogenic pulmonary edema. Asphyxiants further compound the injury in smoke inhalation victims. Simple asphyxiants, such as carbon dioxide and methane, will produce an oxygen-deprived environment. Systemic asphyxiants, such as CO, cyanide, and hydrogen sulfide (H2S), will prevent utilization of oxygen by cells. Either mechanism will promote an anaerobic state and the development of lactic acidosis. CO is a colorless, odorless, nonirritating gas produced by the incomplete combustion of hydrocarbons and petroleum distillates, whether from a fire, fuel source, or automobile exhaust or from the metabolism of methylene chloride, a solvent commonly used as a paint stripper. One of the major mechanisms of CO toxicity is its affinity to bind hemoglobin, with an affinity estimated to be approximately 250 times greater than that of oxygen, which results in reduction in oxyhemoglobin. The impairment in delivery of oxygen is exacerbated by displacement of the oxygen dissociation curve to the left. Furthermore, CO interferes with cellular respiration by binding to mitochondrial cytochrome oxidase and is involved in the formation of oxygen free radicals and subsequent lipid peroxidation. All the aforementioned mechanisms produce oxidative stress on the brain, the main organ affected by CO; excitatory amino acids such as glutamate are activated, which results in neuronal injury and cell death. Areas of the brain that are highly sensitive to hypoxemia, such as the basal ganglia, appear to sustain the most injury. CO is known to bind to myoglobin as well, a feature that contributes to impairment in myocardial contractility. Fetal hemoglobin is more • The majority (50% to 80%) of deaths attributable to fire are caused by smoke inhalation rather than burns. • Smoke is a combination of heated particles and gases (toxicants). • Carbon monoxide has been implicated in more smoke inhalation deaths than any other single compound. • In addition to inhalation of toxicants, smoke inhalation can cause upper airway burns that result in pulmonary parenchymal injury. • The mainstay of treatment consists of ventilator support, early intubation, optimization of fluid resuscitation, pulmonary hygiene, and treatment of specific toxicants. KEY POINTS