Carboxyhemoglobin (Carbon Monoxide [CO])

Carbon monoxide (CO) is a colorless, odorless, gaseous substance found in tobacco smoke, automobile exhaust, fires burning with poor ventilation, improperly functioning furnaces, and defective gas-burning appliances such as stoves. When the hemoglobin of the blood is exposed to CO through inhalation, carboxyhemoglobin is formed. The affinity of hemoglobin for CO is over 200 times greater than for oxygen. Thus, hemoglobin is prevented from combining with, and transporting, oxygen to such tissues as the brain. This results in a lack of oxygen being released in the tissues of the body, a condition known as hypoxia. Symptoms of CO poisoning vary with the carboxyhemoglobin level. Levels of 20% to 30% cause headache, dizziness, nausea, vomiting, and impaired judgment. Levels of 30% to 40% result in confusion, muscle weakness, hyperpnea, hypotension, and tachycardia. When levels reach 50% to 60%, there is a loss of consciousness and possible seizures, and with values greater than 60%, respiratory arrest and death may occur.