* Pulse oximeters: These devices are commonly clipped onto a finger to measure the oxygen saturation in your blood. The polish can block the light from the oximeter, leading to inaccurate readings. If the medical staff cannot accurately monitor your oxygen levels, they might not be able to respond to any complications that arise during the procedure.
* Nail bed assessment: Anesthesiologists also use your nail beds to visually assess your circulation. Polish can hide signs of cyanosis (a bluish discoloration indicating low oxygen levels).
For these reasons, medical professionals usually ask patients to remove nail polish before surgery, particularly on at least one finger.