Which factors can cause falsely low pulse oximetry readings?

• A. Poor peripheral perfusion, motion, and nail polish/artificial nails; bright ambient light can also affect
• B. Correct sensor placement and stable lighting
• C. Adequate perfusion with no movement
• D. Using a pediatric sensor on an adult

Answer: (A)

Pulse oximetry relies on a clean optical signal through a vascular bed, so readings can be falsely low when the signal quality is compromised. Poor peripheral perfusion, such as from cold extremities or vasoconstriction, weakens the pulsatile signal the device uses to calculate saturation, making the reading appear lower than it truly is. Movement distorts the waveform and interferes with separating arterial blood flow from noise, which can push the result downward. Nail polish or artificial nails alter how light is absorbed or blocked, throwing off the red-to-infrared ratio the device relies on. Bright ambient light can flood the sensor and introduce stray photons, further distorting the measurement toward a lower value in some devices.

Under good conditions—proper sensor placement, stable lighting, adequate perfusion, and minimal movement—the readings are reliable. A pediatric sensor on an adult can cause measurement errors due to an improper fit or sizing, which is a separate source of inaccuracy.