A 60-year-old male complains of severe headaches,

A 60-year-old male complains of severe headaches, nausea, dizziness, and a diminution in vision. He has a decrease in oxygen (O2)-carrying capacity without a change in the PO2 of arterial blood. Which of the fol- lowing might account for these findings?

Sulfur dioxide

Ozone

Nitrogen dioxide

Carbon monoxide (CO)

Methane

The answer is d. (Hardman, pp 1676–1678. Katzung, pp 990–991.)

Carbon monoxide is a common cause of accidental and suicidal poisoning. Its affinity for hemoglobin is 250 times greater than that of O2. It therefore binds to hemoglobin and reduces the O2-carrying capacity of blood. The symptoms of poisoning are due to tissue hypoxia; they progress from headache and fatigue to confusion, syncope, tachycardia, coma, convulsions, shock, respiratory depression, and cardiovascular collapse. Carboxyhemoglobin levels below 15% rarely produce symptoms; above 40%, symptoms become severe. Treatment includes establishment of an airway, supportive therapy, and administration of 100% O2. Sulfur dioxide, ozone, and nitrogen dioxide are mucous membrane and respiratory irritants. Methane is a simple asphyxiant.