SpO2 Wavelengths 660 940 — FRCA Primary MCQ

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EasyPhysics & Clinical MeasurementSpO2 Wavelengths 660 940FRCA Primary

Pulse oximetry uses light at which two wavelengths?

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Correct answer: C — 660 nm and 940 nm

Pulse oximetry uses red (660 nm) and infrared (940 nm). Deoxyhaemoglobin absorbs more red / oxyhaemoglobin absorbs more infrared. The isobestic point where both absorb equally is at 805 nm. Carboxyhaemoglobin absorbs similarly to oxyhaemoglobin at 660 nm causing falsely high readings.

Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment