A pulse oximeter is a medical device that measures heart rate and the oxygen level in the blood, expressed as the percent of oxygen saturation. Pulse oximeters operate by shining light through the skin to the blood vessels below. These devices are routinely used in many health care settings and are available over the counter. A high oxygen saturation -- close to 100 percent -- indicates that the red blood cells are fully loaded with oxygen from the lungs.
To ensure proper function, read the manual for your specific pulse oximeter. Remove nail polish, especially dark colors, before placing the sensor on the finger. Place the sensor on the finger before turning on the pulse oximeter for a faster result. Pulse oximeters are less accurate if there is poor blood flow to the finger. This may occur if the person is cold, has very low blood pressure or is having a heart attack. Carbon monoxide -- due to smoke inhalation, carbon monoxide poisoning or heavy cigarette smoking -- results in falsely high pulse oximeter readings. Altitude may result in lower percent oxygen saturation due to the lower oxygen pressure in the air, particularly if you have recently arrived.
A normal percent oxygen saturation reading is in the 95 to 100 percent range. In the event of a low oxygen saturation measurement, look for signs of respiratory distress. This includes shortness of breath, wheezing, difficulty breathing or a bluish discoloration of the face, lips or fingernails. Seek medical attention right away if the respiratory distress is a new or uncomfortable symptom. if it's getting worse or if the pulse oximeter measurement is below 90 percent.