Which factor can affect pulse oximetry readings besides poor perfusion and motion?

• A. Bright ambient light
• B. High humidity
• C. Noise level in room
• D. Temperature of room

Answer: (A)

Pulse oximetry works by emitting two wavelengths of light and measuring how much is absorbed by pulsatile arterial blood. The device assumes the only light reaching the detector comes from its own probe, so bright ambient light can flood the sensor with external photons and distort the detected absorption ratio. This direct interference with the optical signal leads to inaccurate SpO2 and sometimes heart-rate readings, even when perfusion and movement are not the issue. The other factors listed don’t directly disrupt the light measurement in the same way: humidity, room noise, or room temperature can affect comfort, contact, or perfusion indirectly, but they don’t distort the optical signal as ambient light does.