What can cause a false reading on a pulse oximeter?

A pulse oximeter measures the oxygen saturation of hemoglobin in the blood by analyzing the absorption of light at specific wavelengths. Carbon monoxide (CO) can cause a false reading on a pulse oximeter because it binds to hemoglobin with a greater affinity than oxygen, forming carboxyhemoglobin. This compound can be misinterpreted by the pulse oximeter as oxyhemoglobin, leading to an erroneously high saturation reading.

For instance, a pulse oximeter reading might indicate that an individual has a normal or high level of oxygen saturation, while in fact, they may be suffering from carbon monoxide poisoning, which can be life-threatening.

Other substances like alkalis or acids do not have a similar effect on hemoglobin's light absorption characteristics in a way that would significantly interfere with pulse oximeter readings. Cyanide also affects the body's ability to utilize oxygen, but it does not interfere directly with the hemoglobin readings in the same manner as carbon monoxide.