**Question:** Carbon monoxide poisoning causes

**Core Concept:** Carbon monoxide (CO) is a colorless, odorless, and tasteless gas produced when organic matter (such as wood, coal, or oil) is burned incompletely. It binds to hemoglobin, reducing the availability of oxygen for tissues and organs.

**Why the Correct Answer is Right:** Carbon monoxide poisoning results from inhaling elevated levels of carbon monoxide. It binds to the heme group in hemoglobin, forming carboxyhemoglobin (COHb). This reduces the capacity of hemoglobin to bind oxygen, leading to hypoxia (oxygen deprivation) in tissues and organs.

**Why Each Wrong Option is Incorrect:**

A. False: Carbon monoxide poisoning does not primarily affect the central nervous system (CNS) due to its affinity for hemoglobin, causing systemic hypoxia.
B. False: While COHb levels may increase, carbon monoxide poisoning results from a deficiency of oxygen, not an excess of it.
C. False: COHb levels may increase, but the primary mechanism of carbon monoxide poisoning is hemoglobin binding and subsequent tissue hypoxia.
D. False: Although COHb levels may increase, the primary cause of carbon monoxide poisoning is hemoglobin binding, leading to systemic hypoxia rather than increased carboxyhemoglobin levels.

**Clinical Pearl:** Carbon monoxide poisoning is a significant cause of preventable morbidity and mortality worldwide. It highlights the importance of proper ventilation in indoor spaces, especially when using combustion sources.

**Correct Answer:** D. False: Carboxyhemoglobin levels may increase, but the primary mechanism of carbon monoxide poisoning is hemoglobin binding and subsequent tissue hypoxia.