Which hypoxia is associated with carbon monoxide exposure?

• A. Hypoxic hypoxia.
• B. Anemic (hypemic) hypoxia.
• C. Histotoxic hypoxia.
• D. Stagnant hypoxia.

Answer: (B)

Carbon monoxide exposure reduces the blood’s ability to carry oxygen. CO binds to hemoglobin with a much higher affinity than oxygen, forming carboxyhemoglobin and occupying binding sites that would normally carry O2. This lowers the total amount of O2 that blood can deliver to tissues (O2 content drops) and, because the remaining hemoglobin loses in releasing O2 to tissues, the delivery is further hampered. The arterial PO2 can remain normal, so oxygen tension isn’t the problem—the transportation capacity is. That combination fits hypemic (anemic) hypoxia, where the blood’s oxygen-carrying capacity is impaired.

Other types don’t fit CO poisoning as well: hypoxic hypoxia arises from low PO2, histotoxic hypoxia from cells being unable to use O2, and stagnant hypoxia from poor circulation. CO poisoning mainly alters oxygen carrying, not the amount of dissolved O2, tissue utilization, or blood flow.