The inhalation of gases and fumes may cause hyxia and metabolic injury. Inhalation of concentrated gases normally found in the atmosphere, such as carbon dioxide, nitrogen, or meth ane, causes replacement of alveolar but these gases are not toxic.
Carbon monoxide(CO) poisoning is a common and frequently unsus pected cause of inhalational injury and results in tissue globin. competitively displacing oxygen from hemoglobin.
Affinity for ing sites is approximately 250 times greater than that of oxygen. The correlation between CO levels and symptoms is weak, but generally patients with levels greater than 30% are symptomatic. Much lower levels may cause neuropsychiatric symptoms and myocardial ischemia in persons with underlying coronary artery disease. The neuropsychiatric symptoms range from mild confusion or fatigue, usually accompanied by headache and nausea, to profound coma and death. Long-term neurologic sequelae are common and unpredictable. The diagnosis of CO poisoning is made on clinical grounds and supported by laboratory data. A history of other family members with the same symptoms, symptoms occurring in a closed automobil, or an exposure to kerosene heaters or charcoal fires in closed spaces should prompt further evaluation. Laboratory evaluation requires an arterial blood gas with a measured, not calculated hemoglobin oxygen saturation. A CO level should be measured in patients with a measured oxygen saturation(Saoa) lower than the calculated (Sao2) obtained from the oxygen tension(Pao2). Be aware that victims of CO oisoning may have very low CO levels if sufficient time has elapsed since exposure. Nonetheless, it is important to take an in-depth history to prevent further exposure. Treatment of patients with elevated CO levels is with 100% inspired oxygen, which lowers the elimination from approximately 3 hours to 1.5 hours or There is great individual variation in the rate of Co elimination. Treatment with hyperbaric oxygen decreases the elimination half-life to less than 30 minutes, but studies of the clinical utility of this therapy are conflicting.
Inhalation of caustic substances such as ammonia, chlorine, and hydrogen fluoride causes acute symptoms of eye and upper airway inflammation. Pain, lacrimation, rhinorrhea, and upper airway symptoms cause the indi vidual to flee the environment, preventing further exposure and injury. Lower airway injury is usually not severe unless the exposure is massive or the victim is trapped.
Subsequent reactive airways disease may occur and last months.