A pulse oximeter is a device that measures oxygen saturation level. Oxygen saturation is the amount of oxygen that red blood cells carry which then attaches to haemoglobin molecules. Pulse oximeters are easy to use but some things can affect the accuracy of an oximeter reading.
Carbon monoxide can negatively affect a pulse oximeter reading. When carbon monoxide molecules attach to haemoglobin (called carboxyhemoglobin), they replace oxygen molecules. Consequently, there will not be an adequate amount of oxygen attaching to haemoglobin to be carried by the red blood cells. A pulse oximeter doesn't detect the difference between carboxyhemoglobin and normal oxygenated haemoglobin. A combination of 15 per cent carboxyhemoglobin and 80 per cent regular oxygenated haemoglobin would result in a pulse oximeter reading of 95 per cent. For this reason a pulse oximeter should not be used on people with smoke inhalation, suspected carbon monoxide poisoning or heavy cigarette smokers.
A pulse oximeter detects a pulse and oxygenation status from the pulsating arterial blood flow. If the blood flow isn't getting to the tissues properly, then the oximeter won't give accurate readings. This can occur in poor perfusion conditions such as hypotension (low blood pressure), hypothermia (low body temperature) and hypovolemia (low blood volume), as well as cardiac arrhythmias, peripheral vascular disease and heart failure. In these conditions, there still may be sufficient oxygen saturation, but the haemoglobin may have an insufficient oxygen-carrying capability. Because of this, the oximeter may not be able to detect the typical arterial pulsations.
Ambient light may also lead to inaccurate readings in a pulse oximeter. When the room is too brightly lit from light sources -- such as fluorescent, incandescent, quartz-halogen and infrared -- it may interfere with the oximeter's light waves. However, according to RC Journal, even though those light sources produce wavelengths in the same range as a pulse oximeter, it doesn't necessarily mean they will interfere with the oximeter's readings. In an RC Journal study, the data suggested "that ambient light in the clinical setting has no clinically important effect on pulse oximeter readings."
Pulse oximeters function by detecting the pulsations of arterial blood flow by emitting a light wavelength. If anything interferes with that light, including nail polish and fake nails, the oximeter won't be able to detect the arterial blood flow pulsations as easily, thus providing inaccurate readings. Although there isn't conclusive evidence that this is the case, it's still best to remove nail polish or fake nails to get the most accurate readings possible.