Which poisoning involves a toxic gas that reduces oxygen delivery to the body's tissues?

• A. Carbon Monoxide Poisoning
• B. Cyanide Poisoning
• C. Methemoglobinemia
• D. Opioid Overdose

Answer: (A)

This question tests how a gas can reduce oxygen delivery to tissues. Carbon monoxide binds hemoglobin with very high affinity, forming carboxyhemoglobin, which lowers the blood’s capacity to carry oxygen. It also shifts the oxygen-hemoglobin dissociation curve to the left, so the remaining hemoglobin holds onto oxygen more tightly and releases less to tissues. The net result is tissue hypoxia even if arterial oxygen levels look normal. Other options involve different ways oxygen delivery or utilization is impaired—cyanide blocks cellular respiration, methemoglobinemia reduces the amount of usable hemoglobin, and opioid overdose mainly causes hypoventilation—so the gas that most directly reduces oxygen delivery by binding to hemoglobin is carbon monoxide. Treatment focuses on delivering high concentrations of oxygen, and hyperbaric oxygen can be used in severe cases.