Which factor can cause a pulse oximeter reading to falsely appear elevated, potentially masking hypoxemia?

Which factor can cause a pulse oximeter reading to falsely appear elevated, potentially masking hypoxemia?

• A. Carbon monoxide exposure
• B. Anemia
• C. Severe dehydration
• D. Hypovolemia

Answer: (A)

Pulse oximetry estimates how much of the hemoglobin in arterial blood is carrying oxygen by shining two wavelengths of light through the skin and distinguishing oxyhemoglobin from deoxyhemoglobin. The problem arises when other forms of hemoglobin are present that absorb light similarly. Carbon monoxide binds tightly to hemoglobin to form carboxyhemoglobin, and this form absorbs light in a way that mimics oxyhemoglobin. Because the device can’t tell CO-bound hemoglobin from oxygen-bound hemoglobin, it reports a high SpO2 even though the blood’s overall oxygen content is actually impaired. In carbon monoxide poisoning, tissues can be hypoxic despite an apparently normal or elevated reading, which is why this factor can mask hypoxemia. Anemia affects the amount of hemoglobin but not the saturation percentage, so SpO2 can remain normal even with reduced oxygen-carrying capacity. Dehydration or low perfusion can make readings unreliable, but they don’t inherently produce a falsely elevated SpO2 in the way CO exposure does.

Pulse oximetry estimates how much of the hemoglobin in arterial blood is carrying oxygen by shining two wavelengths of light through the skin and distinguishing oxyhemoglobin from deoxyhemoglobin. The problem arises when other forms of hemoglobin are present that absorb light similarly. Carbon monoxide binds tightly to hemoglobin to form carboxyhemoglobin, and this form absorbs light in a way that mimics oxyhemoglobin. Because the device can’t tell CO-bound hemoglobin from oxygen-bound hemoglobin, it reports a high SpO2 even though the blood’s overall oxygen content is actually impaired. In carbon monoxide poisoning, tissues can be hypoxic despite an apparently normal or elevated reading, which is why this factor can mask hypoxemia. Anemia affects the amount of hemoglobin but not the saturation percentage, so SpO2 can remain normal even with reduced oxygen-carrying capacity. Dehydration or low perfusion can make readings unreliable, but they don’t inherently produce a falsely elevated SpO2 in the way CO exposure does.