When preparing for a surgical procedure, patients are routinely asked to remove all fingernail polish, especially dark colors. This pre-operative instruction is not about aesthetics; it is a direct measure to ensure continuous and accurate monitoring of a patient’s oxygen levels throughout the operation. Tracking oxygen saturation is a fundamental component of patient safety during medical intervention.
The Critical Need for Oxygen Monitoring
General anesthesia temporarily depresses a patient’s respiratory drive and circulatory function, making real-time oxygen tracking mandatory. The primary device used for this surveillance is the pulse oximeter, which typically clips painlessly onto a finger. This device measures the percentage of hemoglobin carrying oxygen, known as peripheral oxygen saturation (SpO2). This measurement gives clinicians immediate insight into oxygen delivery and transport efficiency. Any sudden drop signals a potentially dangerous change in the patient’s status that requires immediate intervention by the anesthesia team.
How Nail Polish Interferes with Equipment
The pulse oximeter operates by emitting two specific wavelengths of light—red (around 660 nm) and infrared (around 940 nm)—through the patient’s fingertip. Sensors on the opposite side of the clip measure how much light passes through the tissue, differentiating between oxygenated and deoxygenated hemoglobin. Any layer of nail polish acts as a physical barrier that the light must penetrate. This opaque coating attenuates the light signal before it can reach the sensor. This interference can result in a complete failure to obtain a reading or lead to inaccurate or unreliable data.
Why Dark Pigments Are Especially Problematic
Darker nail polish colors, such as black, blue, green, and deep purple, are particularly troublesome because they contain dense pigments that absorb light significantly. These chemical components absorb light at the specific red and infrared wavelengths used by the pulse oximeter. This high absorption can be misinterpreted by the device’s algorithm, sometimes mimicking the absorption pattern of deoxygenated blood. For instance, certain blue and green polishes absorb more light at the red wavelength than the infrared wavelength, which is the signature pattern of lower blood oxygen. As a result, the oximeter might display a falsely low oxygen saturation reading, which could cause unnecessary concern or treatment delays.
Considerations for Acrylics, Gels, and Alternative Sites
Artificial nails, including gels and acrylics, present a separate challenge due to their increased thickness and opacity. Although some studies suggest unpolished acrylics may not significantly affect readings, their bulk and potential for polish underneath still pose a risk to the signal. Clinicians often recommend removing artificial nails from at least one finger to ensure a reliable primary monitoring site. If removal is impossible, alternative monitoring locations can be used, such as the earlobe, toe, or nose. These alternative sites allow the light to pass through tissue without fingernail coating interference, though standard practice favors clearing a finger for assessment.