Which statement about two-wavelength oximetry is true?

Which statement about two-wavelength oximetry is true?

• A. It uses multiple wavelengths to measure all hemoglobin species
• B. It uses two wavelengths to calculate a red-to-infrared ratio to estimate saturation
• C. It can only measure arterial oxygen tension
• D. It is invasive

Answer: (B)

Two-wavelength oximetry uses two specific light wavelengths to exploit how oxyhemoglobin and deoxyhemoglobin absorb red and infrared light differently. By sending red and near-infrared light through tissue and measuring the pulsatile changes in absorption, the device forms a ratio of red-to-infrared absorption. This ratio is then mapped to an arterial oxygen saturation (SpO2) estimate. Because it assesses how much oxygen is bound to hemoglobin rather than the actual dissolved oxygen in blood, it provides a saturation reading, not a direct measurement of arterial oxygen tension (PaO2). It’s noninvasive, typically using a fingertip or earlobe sensor. It also assumes the dominant species are oxy- and deoxyhemoglobin, so readings can be biased by other hemoglobin species unless corrections are included.

Two-wavelength oximetry uses two specific light wavelengths to exploit how oxyhemoglobin and deoxyhemoglobin absorb red and infrared light differently. By sending red and near-infrared light through tissue and measuring the pulsatile changes in absorption, the device forms a ratio of red-to-infrared absorption. This ratio is then mapped to an arterial oxygen saturation (SpO2) estimate. Because it assesses how much oxygen is bound to hemoglobin rather than the actual dissolved oxygen in blood, it provides a saturation reading, not a direct measurement of arterial oxygen tension (PaO2). It’s noninvasive, typically using a fingertip or earlobe sensor. It also assumes the dominant species are oxy- and deoxyhemoglobin, so readings can be biased by other hemoglobin species unless corrections are included.