Co-oximetry can differentiate which hemoglobin species that two-wavelength oximetry cannot?

Co-oximetry can differentiate which hemoglobin species that two-wavelength oximetry cannot?

• A. HbO2 only
• B. HbO2 and Hb only
• C. COHb and MetHb
• D. Hb and MetHb

Answer: (C)

The main idea is that two-wavelength pulse oximetry estimates oxygen saturation by assuming only two forms of hemoglobin are present: oxyhemoglobin and deoxyhemoglobin. Because their spectra at those two wavelengths can be similar, the device cannot tell apart other species that also absorb light, like carboxyhemoglobin (COHb) and methemoglobin (MetHb). This limitation can lead to misleading readings when COHb or MetHb are present. Co-oximetry, however, uses multiple wavelengths across a broader spectrum and solves for the amounts of several hemoglobin species simultaneously. Each species has a unique absorption pattern across those wavelengths, so the device can separately quantify HbO2, Hb, COHb, and MetHb. That capability is why co-oximetry can differentiate COHb and MetHb, whereas a two-wavelength oximeter cannot.

The main idea is that two-wavelength pulse oximetry estimates oxygen saturation by assuming only two forms of hemoglobin are present: oxyhemoglobin and deoxyhemoglobin. Because their spectra at those two wavelengths can be similar, the device cannot tell apart other species that also absorb light, like carboxyhemoglobin (COHb) and methemoglobin (MetHb). This limitation can lead to misleading readings when COHb or MetHb are present.

Co-oximetry, however, uses multiple wavelengths across a broader spectrum and solves for the amounts of several hemoglobin species simultaneously. Each species has a unique absorption pattern across those wavelengths, so the device can separately quantify HbO2, Hb, COHb, and MetHb. That capability is why co-oximetry can differentiate COHb and MetHb, whereas a two-wavelength oximeter cannot.