As the amount of attached carbon monoxide increases in the body to approximately 20 percent of the maximum potential, the patient develops a terrible headache, nausea, vomiting, and a loss manual dexterity. At 30 percent, the level of consciousness descends into irritability, impaired judgment, and confusion. It will be increasingly difficult for him to get a full breath, and he will grow drowsy. At 40 to 60 percent, the patient lapses into a coma. Levels above 60 percent are usually fatal.
Death typically results from heart failure.
Death by CO is not a pleasant drift into slumber depicted in some movies. If you have been exposed to low concentrations of CO, you'll probably recover completely in a few hours. The half-life of carbon monoxide attached to hemoglobin runs around 5.5 hours. If the concentrations have been high, you may die even removed from the source of the gas. Rapid evacuation to a high pressure chamber and high concentrations of supplemental oxygen are necessary.