CO binds to blood about how many times greater than oxygen?

• A. 50
• B. 100
• C. 200
• D. 300

Answer: (C)

Carbon monoxide binds to hemoglobin far more readily than oxygen does—about 200 times greater. This means CO can occupy the available binding sites on hemoglobin at much lower concentrations, forming carboxyhemoglobin and drastically reducing the blood’s capacity to carry oxygen. The higher affinity also shifts the oxygen–hemoglobin dissociation curve to the left, making it harder for hemoglobin to release oxygen to tissues. The result is tissue hypoxia even if the partial pressure of oxygen is normal, which is why CO poisoning can be so dangerous. In practice, rapid administration of 100% oxygen is used to displace CO, with hyperbaric oxygen considered in severe cases.