In carbon monoxide poisoning, which statement best explains why pulse oximetry can be misleading?

In carbon monoxide poisoning, which statement best explains why pulse oximetry can be misleading?

• A. CO displaces oxygen from Hb causing hypoxia that is NOT REFLECTED BY A PULSE OX
• B. The pulse oximeter cannot differentiate carboxyhemoglobin from oxyhemoglobin, so readings may be normal despite hypoxia
• C. CO poisoning increases the pulse oximetry accuracy
• D. CO has no effect on Hb

Answer: (B)

Pulse oximetry works by measuring how much hemoglobin is carrying oxygen using light absorption at two wavelengths. In carbon monoxide poisoning, carbon monoxide binds to hemoglobin to form carboxyhemoglobin, which reduces the blood’s oxygen-carrying capacity. The crucial point is that standard pulse oximeters cannot distinguish carboxyhemoglobin from oxyhemoglobin because these forms absorb light in a way that looks the same to the device. As a result, the SpO2 can read as normal or near normal even though tissues are not getting enough oxygen, giving a misleading impression of adequate oxygenation. To truly assess CO exposure, you need co-oximetry (often via arterial blood gas analysis) to measure the percentage of carboxyhemoglobin. Management focuses on delivering high-flow oxygen and may involve hyperbaric oxygen therapy depending on severity.

Pulse oximetry works by measuring how much hemoglobin is carrying oxygen using light absorption at two wavelengths. In carbon monoxide poisoning, carbon monoxide binds to hemoglobin to form carboxyhemoglobin, which reduces the blood’s oxygen-carrying capacity. The crucial point is that standard pulse oximeters cannot distinguish carboxyhemoglobin from oxyhemoglobin because these forms absorb light in a way that looks the same to the device. As a result, the SpO2 can read as normal or near normal even though tissues are not getting enough oxygen, giving a misleading impression of adequate oxygenation. To truly assess CO exposure, you need co-oximetry (often via arterial blood gas analysis) to measure the percentage of carboxyhemoglobin. Management focuses on delivering high-flow oxygen and may involve hyperbaric oxygen therapy depending on severity.