Which factor could cause a falsely low SpO2 reading due to sensor placement?

• A. Finger could be cold
• B. The patient is overweight
• C. The monitor is new
• D. The room is bright

Answer: (A)

Pulse oximetry depends on a good, pulsatile signal from the sensor site. When the finger is cold, blood vessels constrict and peripheral perfusion drops, which weakens the pulsatile signal the sensor relies on. That weak signal can lead the device to misread the ratio of absorbed light and display a falsely low SpO2. Warming the hand, ensuring the sensor is well seated and in good contact, and avoiding sites with poor perfusion helps prevent this. The other factors listed don’t directly relate to sensor contact and perfusion in a way that would consistently cause a falsely low reading.