Which dye has the greatest impact on pulse oximeter readings?

Which dye has the greatest impact on pulse oximeter readings?

• A. Methylene Blue
• B. Indigo Carmine
• C. Eosin Y
• D. Fluorescein

Answer: (A)

Pulse oximetry relies on two wavelengths of light, roughly red (about 660 nm) and infrared (about 940 nm), to distinguish oxyhemoglobin from deoxyhemoglobin. Any dye present in the blood that absorbs light at those wavelengths will distort the measured ratio and skew SpO2 readings. Methylene blue absorbs strongly in the red region, directly overlapping the red beam the device uses, so it can cause a pronounced, artificial change in SpO2—often a falsely low or unstable reading. The other dyes either do not absorb as much at the red/infrared wavelengths or their absorption is outside the two wavelengths used by the sensor, so their impact is much less. For example, fluorescein mainly absorbs blue/green light and has little effect on red/infrared measurements, while eosin Y and indigo carmine have absorption characteristics that don’t interfere as significantly with the two used wavelengths.

Pulse oximetry relies on two wavelengths of light, roughly red (about 660 nm) and infrared (about 940 nm), to distinguish oxyhemoglobin from deoxyhemoglobin. Any dye present in the blood that absorbs light at those wavelengths will distort the measured ratio and skew SpO2 readings. Methylene blue absorbs strongly in the red region, directly overlapping the red beam the device uses, so it can cause a pronounced, artificial change in SpO2—often a falsely low or unstable reading. The other dyes either do not absorb as much at the red/infrared wavelengths or their absorption is outside the two wavelengths used by the sensor, so their impact is much less. For example, fluorescein mainly absorbs blue/green light and has little effect on red/infrared measurements, while eosin Y and indigo carmine have absorption characteristics that don’t interfere as significantly with the two used wavelengths.